Chemistry HSC Full Notes BEST NOTES
Chemistry HSC Full Notes BEST NOTES
Chemistry HSC Full Notes BEST NOTES
Note: This is not the final revision of my notes (I’m constantly revising them as I do papers), and
there may be a few areas of error or unclear explanations. However, I’ve gone through it a number
of times, and it should be mostly very accurate and comprehensive. If you find anything wrong, it
would be nice if you could tell me on korenxii@hotmail.com so I can either discuss it or change it.
Good luck for the HSC guys
Hydrocarbons
When all bonds are single, they are called alkanes. This is a family of compounds, represented by a
general formula CnH2n+2, aka a homologous series. They have similar properties and reactions.
There are ‘straight’ chain alkanes.
e.g.
C C C
C C C
The 109o, zig-zag bonding shape is due to the tetrahedral nature of single bonds. Carbon atoms
always form 4 bonds. If they don’t you’re doing something wrong.
C C
C C C
Methane, CH4, ethane, C2H6, Propane, C3H8, and Butane, C4H10 are all alkanes.
Physical Properties
C1 to C4 are gases at room temp, C5 to C18 are colourless liquids, others are solids.
The density of alkanes are significantly less than water (1.00g/mL), are non-conductors of
electricity and are insoluble in water. The reason for their insolubility is that C-C bonds are non-
polar, and C-H bonds are only slightly. This slight polarity is cancelled by symmetry in structure.
Weak dispersion forces, relatively low boiling/melting points. Boiling/melting points increase as
molecular weight increases, due to stronger dispersion forces (more electrons). Volatility decreases
as molecular weight increases.
Alkenes
Chem notes David Lee BHHS 2007 1
Contain a double bond between a pair of carbon atoms. Homologous series, formula CnH2n, planar
shape. There are different ways of representing structure:
(2)Full Structural Formula – shows planar geometry around double bond, and tetrahedral around
other carbon atom
(3)Intermediate type – infers tetrahedral shape
(4)Condensed structural formula – no attempt to show structure, but enough information is
provided
Isomers are different compounds with the same molecular formula but different structural
formula. The double bond can be at different positions in the compound.
e.g.
Physical Properties
Straight-chain alkenes similar to alkanes. Densities similar to corresponding alkanes, insoluble in
water.
Alkynes
Contain a triple bond between carbons. CnHn-2. As with alkenes, isomers are possible. They are non-
polar, low boiling points and insoluble in water
Functional Group
The functional group of carbon compounds is the most reactive area of the compound. In alkenes
and alkynes, the double/triple bonds are the functional groups. When a hydrogen atom is replaced
with a halogen atom, e.g. OH, the halogen becomes the functional group.
Molecules with a particular functional group react similarly, regardless of the attached
chains.
Chem notes David Lee BHHS 2007 2
Alkanols are alkanes with one H replaced by an OH group. They are named with the ‘e’ replaced by
an ‘ol’, and a prefix number to denote the position of the hydroxyl group. This group is the
functional group, and provides high melting/boiling points due to polar bonds.
Primary alcohols have one carbon bound to the carbon w/ OH group, secondary have two and
tertiary have three. Extent of hydrogen bonding depends on exposure of OH group, most exposed in
primary, highest boiling/melting points etc.
• Construct word and balanced formulae equations of chemical reactions as they are
encountered
• Identify the industrial source of ethylene from the cracking of the fractions from the
refining of petroleum
Ethylene is produced from natural gas or crude oil (mixtures of hydrocarbons, containing mainly
alkanes and cycloalkanes and smaller amounts of unsaturated including alkenes), which is called
feedstock. The feedstock is refined by fractional distillation to obtain alkenes since alkanes are
susceptible to combustion and unreactive (not useful as starting material).
Ethylene is the most versatile, but not found in large quantities in feedstock. Produced from other
hydrocarbons in ‘cracking’ (a process where hydrocarbons of higher mol mass are converted to
lower mol mass via breaking of chemical bonds). There is greater demand for some fractions than
others (e.g. gasoline > heavier hydrocarbons), and fractions from crude oil are not in optimum
ratios, hence cracking. Note that air needs to be excluded to prevent combustion. Ethylene is simple
and can be synthesised from many different hydrocarbons. Three ways:
1. Thermal cracking – requires very high temps and generally not used. End products hard to
control since many places where bonds could break, early method. Accelerates reaction and
drives equilibrium to reactants.
2. Catalytic cracking of fractions separated from petroleum. – material is passed over a
catalyst at a temperature of about 500oC, and the particles adsorb onto the catalyst and have
their bonds weakened, resulting in decomposition. E.g. C10H22(g) -> C8H18(g) + C2H4(g). Alkane
splits further into smaller alkenes until propene/ethylene formed. Catalysts allow it to be
carried out at lower temperatures. Zeolite (by mid 1970’s) is the main catalyst, and is a
crystalline substance of Al, Si and O. Usually fine powder (higher surface area for action of
catalyst) circulated through feedstock. Zeolite gives greater control over products under
different conditions of temperature and pressure (thus increasing yields of desired products)
i.e. C18H38(g) ----(zeolite catalyst)---> 4 C2H4(g) + C10H22(g)
3. Steam cracking of ethane and propane – ethane from natural gas deposits fed into
furnaces with steam, heated between 750 – 900oC causing much ethane to be converted to
ethylene
i.e. C2H6(g) -> C2H4(g) + H2(g)
Propane can also be used:
C3H8(g) -> C2H4(g) + CH4(g)
Ethylene’s C=C double bond is highly reactive, allowing it to react with molecules to form many
useful products
Dilute
H2So4 cat
w/ water
Br2, non
KMnO4, H+
aqueous
Acidified solvent
HCl, non
aqueous
solvent
Reaction of alkenes
Characteristic reaction of alkenes is addition reaction. Two new atoms or groups of atoms are added
across double bond, one to each carbon. The C=C is converted to a single bond and a saturated
hydrocarbon is produced. General eqn:
CuCl +150o C
[2CH2=CH2(g) + Cl2(g) + ½ O2(g) → 2CH2=CH-Cl(g) + H2O(g?)]
2
4) Styrene – produces from benzene and ethylene via the intermediate ethylbenzene
( dilute ) H SO
[CH2=CH2(g) + H2O(l) 4 → CH3-CH2OH(l) ]
2
o
Ag + 250 C
[C2H4(g) + ½ O2(g) → C2H4O(g)]
+
H
[C2H4O(g) + H2O(l) →
OH-CH2-CH2-OH]
• Identify data … to compare the reactivities of appropriate alkenes with the corresponding
alkanes in bromine water
Method:
1). Four semi-micro test tubes were half-filled with bromine water, cyclohexane, cyclohexene and
toluene respectively, using eye droppers
2). Bromine water was mixed with the other substances by placing a few drops of bromine water in
each micro-test tube with a dropper
3). The test tubes were tapped, and observations recorded
Results:
Cyclohexane – none
Cyclohexene – forms clear solution
Toluene – none
The functional group reacting with bromine is the double bond present in alkenes, this
decolourises bromine water. Addition reactions. These reactions are addition reactions:
Bromine w/ water
Br2( aq ) + H 2 O(l ) ←→ HOBr − ( aq ) + H + ( aq ) + Br − ( aq )
Method:
1). Five semi-micro test tubes were filled halfway with tomato juice
2). An eye dropper was used to place 1, 2, 3, 4 and 5 drops of bromine in each of the test tubes
respectively
3). The solutions were stirred with the stirring rod until colour appeared
4). The colours and the corresponding amounts of bromine water in each test tube were recorded
Results:
Test tube no. No. of drops of Bromine Colour
1 10 Blue
2 8 Turquoise
3 6 Green
4 4 Khaki
5 2 Orange
Varying amounts of bromine in tomato juice changes the number of delocalised electrons in
lycopene molecules, changing the spectrum of colours absorbed and resulting in different reflected
visible spectra
• Identify that ethylene serves as a monomer from which polymers are made
Ethylene serves as a monomer due to the reactivity of its double bond. It has a structure that can
change to accommodate the additional bond needed to join repeating units together.
• Identify polyethylene as an addition polymer and explain the meaning of this term
General outline: Ethylene can be changed from gas to liquid under high pressure. This liquid
ethylene can be heated in the presence of a catalyst to form polyethylene.
Two forms of polyethylene can be produced, each with differing methods and varying properties:
o LDPE (reaction conditions 100 – 300oC, 1500 – 3000 atm) – Polymerisation consists
of three stages
Initiation – organic peroxide catalyst. They produce free radicals (molecules
with unpaired electron), such as H-O. which is a hydroxy radical. This causes
the double bond in ethylene to break and form a bond with the radical.
CH2=CH2 +R● RCH2-CH2●
Propagation - The resulting
molecule contains an unpaired
electron. Bonds to another
ethylene molecule through the
same process etc. (Chain
propagation reactions).
Backbiting, where the chain curls onto itself and the free electrons takes a
hydrogen atom from an existing CH2 group, causes branching.
LDPE HDPE
Higher degree of branching, meaning less Lower degree of branching, meaning
dispersion forces between strands, more dispersion forces within strands,
making it softer and more flexible making it harder and more rigid
Less dense More dense
These products are plastics. Plastics are manufactured materials containing combinations of organic
and inorganic elements. They are solid in the finished state but fluid at some stage, and able to be
formed into shapes by application of heat and/or pressure.
The variable chain length leads to many uses, with shorter lengths for food packaging and milk
containers, to longer lengths (800,000 atoms per molecule) for artificial ice rinks.
• Describe the uses of the polymers made from the above monomers in terms of their
properties
HDPE 1). Can take high pressures 1). Coating in steel pipes
in high pressure gas mains
2). High tensile strength 2). Fibres for ropes, fishing
nets
3). Chemical resistance 3). Moulded into
containers to hold petrol,
oil, detergents and acids
4). Durability and toughness 4). Children’s toys, plastic
buckets, playground
equipment
Polyvinyl 1). Soft and pliable 1). Wallpaper, clothing
Chloride OR (depending on additives) upholstery
2). Rigid 2). Water pipes, guttering
3). Coatings on materials
3). Resists burning to make flameproof
4). Flooring; tiles, roll
4). Low static electricity flooring and carpet
backing
Polystyrene 1). Rigid and electrical insulator 1). Television backing,
--- hairdryers, washing
As foam: machines
2). Chemically unreactive 2). Food containers
3). Low density 3). Marker buoys,
--- surfboards
4). Resists high impact 4). Shoe heels, toys
• Discuss the need for alternative sources of the compounds presently obtained from the
petrochemical industry
Petroleum fractions have been the most convenient and economical raw material for synthetic
polymers. However, alternatives are being sought since:
Chem notes David Lee BHHS 2007 9
1) The current source is non-renewable, and the move to more renewable resources will allow
us to continue manufacturing petrochemical products (supplies will run out)
2) Petrochemical products are (non-biodegradable?) and contribute to the degradation of the
environment
o A solution is the use of biomass (organic material from living organisms). All living
organisms produce biopolymers, which are naturally occurring polymers made
entirely or in large part by living organisms
o They are advantageous since they are renewable, and can be used indefinitely with
careful use, and are biodegradable since the bonds within the molecule can be broken
down by bacteria and fungi, so they do not contribute to the degradation of the
environment.
A condensation polymer is a polymer that was produced through the reaction of two different
functional groups in which a small molecule (usually water) is eliminated and the two groups
become linked together. Condensation reactions involve saturated molecules. Common groups are –
COOH (carboxylic acid), –OH (alcohol) and –NH2 (amine) group. Condensation polymers do NOT
require identical monomers
Practical
Aim: to produce nylon using interfacial polymerisation
Equipment:
2 x 100 mL beakers
Tweezers
Glass stirring rod
20mL of 1,6 – diaminohexane solution
20 mL of 10% sebacoyl chloride in hexane
Procedure:
1). 1,6 – sebacoyl chloride was added to a beaker
2). The diamino hexane was run very carefully down the side of the beaker, so that the two
solutions mix as little as possible
3). The white material formed between the two layers was clamped using the tweezers
4). The material was drawn away from the beaker and onto the glass stirring rod, being careful to
keep away from sides of beaker
5). The material was wound onto the stirring rod, dried and examined
Results/Analysis:
o It is the main component of plant cell wall and major structural component of woody
plants and natural fibres
o This makes it the most abundant polymer known on earth.
• Identify that cellulose contains the basic carbon-carbon structures needed to build
petrochemicals and discuss its potential as a raw material
Cellulose contains three-carbon and four-carbon chains with attached hydrogen and hydroxl groups.
Many polymers such as polypropylene are made from three-carbon and four-carbon monomers. If
cellulose can be broken down and these chains isolated, it can be used to produce polymers. Large
amounts occur naturally such as in plant cell walls, and large amounts left over from agriculture.
• Use available evidence to gather and present data from secondary sources and analyse
progress in the recent development and use of a named biopolymer
o Alcaligenes Eutrophus, a bacteria widely found in soil and water, is fed a precise
combination of glucose and propionic acid, producing PHB’s as energy storage
o The PHB’s are extracted and can be polymerised to create a plastic with properties
similar to polypropylene
• Excellent flexibility and toughness
• Stable in air, humid conditions
• Biodegrades in microbially active environments, bacterial and fungi microorganisms
can utilise PHA’s as a source of energy by breaking it down using enzymes
(depolymerases).
Potential uses
o Biocompatability - useful in several medical applications such as controlled drug release,
medical surtures, bone plates
o Flexibility and toughness - structural materials in packaging products
o Biodegradable – can be used in food packaging, natural breakdown reduces landfill
Development
Current work by Metabolix, successfully engineered bio-factories to demonstrate economic
production of a broad range of PHA’s. Demonstrated fermentation on a tonnage scale, cost to be
under a dollar a pound.
• Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this
process and the catalyst used
• Describe the addition of water to ethylene resulting in the production of ethanol and
identify the need for a catalyst in this process and the catalyst used
• Model the above two processes
• Describe and account for the many uses of ethanol as a solvent for polar and non-polar
substances
Risk Analysis
Hazard Risk Control
Iodine Toxic – fatal if swallowed. Safety glasses, effective
Corrosive, causes burns ventilation
and damaging to lungs if
inhaled
Oxalic acid Poisonous if swallowed, Gloves, avoid generation
inhaled or absorbed of dust
through skin
Method:
1). 20 mL of ethanol was poured into each of 10 test tubes using measuring cylinders
2). A rice-grain amount of each solid was placed into successive test tubes, and a few millilitres of
each liquid placed into the remaining test tubes using an eye dropper.
3). Each test tube was agitated by tapping and gently shaking
4). Observations were recorded
Results:
Solute Solubility
Sodium chloride No
Napthalene Slightly
Cyclohexanol Yes
Glycerol Yes
Iodine Yes, dark red
Oxalic acid Yes, purple
Boric acid Yes
Glucose Yes
Wax No
Urea Yes
Ionic (sodium chloride): Unable to dissolve since strong ionic bonds holding atoms together, and
intermolecular formed inadequately strong to break apart lattice
Polar covalent bonds (cyclohexanol C6H11OH, glycerol C3H5(OH)3, oxalic acid C2O2(OH)2, Boric
acid B(OH)3, Glucose C6H12O6, Urea CO(NH)2) : Polar covalent bonds such as those in hydroxyl
groups allowed ethanol to bond strongly and dissolve them
Macromolecules (Wax C24H50) : Though only held together with weak dispersion forces, its large
size means a larger surface area of contact between molecules and thus more total dispersion forces.
Ethanol was unable to dissolve
Non-polar molecules (Iodine, Napthalene, heptane,
pentane) – iodine is diatomic and has very weak
dispersion forces holding together, but ethanol can
form dispersion forces with iodine molecules and pull
away. Napthalene is an aromatic hydrocarbon and
does not attract strongly, but dissolves in a similar
fashion, same for heptane and pentane which are
short-chain hydrocarbons.
• Outline the use of ethanol as a fuel and explain why it can be called a renewable resource
Ethanol is a flammable liquid, burning with the reaction:
C 2 H 5 OH (l ) + 3O2 ( g ) → 2CO2 ( g ) + 3H 2 O( g )
It is also easily transportable, and was used by hikers and campers. It has thus been proposed as an
alternative fuel source, having already been used as an ‘extender’ in world war 2. The purpose of
ethanol is to:
1. Reduce greenhouse gas emissions
2. Reduce reliability on non-renewable fossil fuels
Engines would not need any modification to run 10-20% ethanol fuel, and is renewable since
synthesised in sugar cane from carbon dioxide, water and sunlight. Burning produces carbon
dioxide and water which can then be re-used to produce ethanol, so it follows an almost indefinite
material cycle.
It has thus been promoted for motor cars to supplement and replace petrol.
• Solve problems, plan and perform a first-hand investigation to carry out the fermentation
of glucose and monitor mass changes
Method:
1). One gram of beef extract and 25 grams of glucose and 7 grams of yeast were measured out using
an electronic beam balance
2). A test tube with barium hydroxide was weighed on the triple beam balance and its weight
recorded
3). The beaker was filled with 300mL of tap water and heated over a bunsen burner until 40oC
4). The beef extract, warm water, yeast and glucose were quickly poured into the conical flask and
weighed on the electronic beam balance
5). The apparatus was set up as shown below:
6). After a week, the tubes and stopper were removed, then
the fermented solution and test tube with barium hydroxide
were weighed on the triple beam balance and analysed
7). Experiment was repeated 2 times
7). Steps 1-6 were repeated without the yeast, to act as a
control
Results:
Result Loss in mass of conical Gain in mass of test tube
flask and contents (g) contents (g)
1 8.0 5.9
2 9.8 4.8
3 9.1 5.0
Average 9.0 5.2
Control:
Result Loss in mass of conical Gain in mass of test tube
flask and contents (g) contents (g)
1 0 0
2 0 0
3 0 0
Average 0 0
Nine grams of carbon dioxide was given off in this experiment (loss in mass of conical flask) the
gain in the test tube was not used since some carbon dioxide escaped through holes around the
stopper.
moles of CO 2
9.0 g
=
(14.01) + (16.00) * 2
= 0.20moles
Through stoichiometry, 1 mole of glucose produced 2 moles of CO2 and ethanol each. Therefore
0.20 moles of ethanol produced
Mass of ethanol = molar mass ethanol x moles produced = 10g (3.3 % w/v)
This reaction did not go to completion, 6 grams of glucose left. This is most likely because the yeast
were saturated in ethanol and could no undergo further fermentation, or were no left for sufficient
time. Some discrepancy could have been caused by measurement error.
• Process information from secondary sources to summarise the processes involved in the
industrial production of ethanol from sugar cane
• Assess the potential of ethanol as an alternative fuel and discuss the advantages and
disadvantages of its use
Note: it is more expensive to dehydrate ethanol than it is to purify ethylene from crude oil (this
doesn’t really go here, I dunno where to shove it)
Disadvantages are:
o Large areas of arable land needed for agriculture, associated land degradation such as
erosion and fertiliser run off
o Blends above 10% shown to be damaging to cars designed for gasoline, including
increased carbon deposits on pistons and corrosion of metallic engine components
o Greenhouse reductions hindered by use of fossil fuels and emission of toxic waste
products in transportation/production of ethanol
Higher blends of ethanol require special engines suited, lower blends (<20%) do not require this. It
is extensively used in some countries, such as Brazil and the US.
o In Brazil, a large portion of cars are currently “flex-fuel”, allowing them to use both
ethanol and gasoline, 80% of cars produced in 2005 were flex-fuel
o Government subsidies and rising petroleum prices have successfully encouraged mass-
uptake of ethanol use. Pure ethanol and 25% ethanol are available at nearly all gas
stations
o Its use has had noticeable improvements on air quality due to more complete combustion
o Brazil is approaching self-sustainability in areas of ethanol use due to its large areas of
arable land and tropical climate
The Bad:
o There are situations where ethanol cannot replace fossil fuels, such as diesel fuels, and
they continue to be burnt
o The popularity of ethanol depends on government subsidies. Production of ethanol
requires a large investment of money and energy, and costs more than petroleum to
produce
o Requires destruction of rainforest which acts as carbon sink, offsets greenhouse
reductions
In Australia:
o Ethanol costs more than petrol to produce, so subsidies are provided to encourage
addition of ethanol to petrol
o Ethanol cars are in a small minority
o Public suspicion about fuel, since some independents add excessive ethanol causing
engine wear, and claims by manufacturers that blends above 10% will void warranties.
Federal government has decided to limit mixtures to max 10% ethanol
Chem notes David Lee BHHS 2007 17
o Skepticism about mass-implementation, no reliable studies showing improvements in air
quality through ethanol industry and worry about associated environmental costs such as
land degradation
o Ethanol uptake is less successful due to lack of arable land for feedstock growth, higher
individual wealth and higher costs of labour
Evaluation:
Highly successive in some countries, but less successful in others with less land resources. Usage is
hindered economically depending on economic situation, and for some is not economically feasible
due to high energy and monetal cost.
• Define the molar heat of combustion of a compound and calculate the value for ethanol
from first-hand data
Molar heat of combustion is the amount of heat energy released when one mole of the substance
undergoes a combustion reaction.
Method:
1). A copper calorimeter and spirit burner were weighed using an electronic beam balance
2). A measuring cylinder was used to pour 100 mL of water into the copper calorimeter
3). The apparatus was set up as show below:
Results:
Molar heats of combustion
Methanol: -410 kJ/mol
Ethanol: -640 kJ/mol
Propanol: -980 kJ/mol
Butanol: -1100 kJ/mol
Ethanol would be the best fuel source since it has the best balance of achieving complete
combustion and burning with more heat per gram.
Safety considerations
Danger in transporting spirit burners – carried only while unlit so would not ignite if dropped and
shattered
Methanol – vapours are toxic in larger doses, do not open spirit burner
Ethanol – skin and eye irritant, wear safety glasses, do not open spirit b urner
Errors:
Experimental results differed from theoretical results due to:
o Conduction and radiation of heat from copper calorimeter into surrounding environment,
reducing heat of combustion values
o Inaccuracies in measuring equipment
A displacement reaction is where a metal converts the ion of another metal to the neutral atom.
• Account for changes in the oxidation state of species in terms of their loss or gain of
electrons
Examining oxidation states is useful in determining whether a redox reaction has occurred during a
chemical reaction. Some elements display multiple oxidation states.
e.g.
In Cu2O (2Cu+, O2-)
Oxidation state of copper is +1
• Outline the construction of galvanic cells and trace the direction of electron flow
• Describe and explain galvanic cells in terms of oxidation/reduction equations
• Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells
The electrode are the conductors of a cell which get connected to an external circuit
The anode is the electrode where oxidation occurs
The cathode is the electrode where reduction occurs
The electrolyte is a substance which in solution or molten conducts electricity
Standard conditions are 1M solution and 25oC. Acidic conditions alter the potential difference.
Process:
1. The electrode with lower reactivity attracts electrons from the other electrode through the
conductor
2. A redox reaction results:
+
→ Cu 2+ ( aq ) + 2 Ag ( s )
e.g. Cu ( s ) + 2 Ag ( aq )
3. The ion formed goes into solution, and the anion dissolves. The metal ions in solution
around the cathode obtain the electron and plate onto the electrode
4. Ions flow from the salt bridge into the electrolyte solutions to neutralise charge and remove
opposing potential difference
o Allows ‘migration’ of charge, and positive ions in the salt bridge move into the negative
solution, and vice versa
o This preserves electric neutrality, and eliminates negative potential difference
Cell diagrams
Type 1:
Metal/metal ion electrode
e.g.
Cu|Cu2+||Ag+|Ag
| = phase separator
|| = salt bridge
Type 2:
Inert substance such as platinum or carbon and equimolar amounts of non-metal and its ion.
e.g.
Chem notes David Lee BHHS 2007 21
Pt(s) | I2(s)|I-(aq) || Fe2+(aq)|Fe3+(aq) | Pt(s)
Reaction progress:
• Perform a first-hand investigation to identify the conditions under which a galvanic cell
is produced
• Perform a first-hand investigation and gather first-hand information to measure the
difference in potential of different combinations of metals in an electrolyte solution
Aim:
1. to construct a galvanic cell called a Daniell cell and investigate conditions under which it
operates (A)
2. to compare the effect of using different combinations of metals in electrodes (B)
3. to compare the effect of different volumes of electrolytes under otherwise identical
conditions (A)
Method A:
1). A zinc strip and copper strip were cleaned with sand paper
2). A half cell consisting of a copper strip resting in a 250 mL beaker half-filled with copper sulfate
solution was constructed
3). A similar cell with a zinc strip and zinc sulfate solution was constructed, and these half-cells
linked with a piece of filter paper soaked with potassium nitrate solution and folded
4). The copper strip was connected to the positive terminal of a voltmeter, and te zinc strip to the
negative terminal
5). The reading and polarity were recorded before quickly disconnecting the voltmeter
6). The beakers were then completely filled with corresponding electrolyte solutions, and the
voltage measured again
Results:
Beakers half: 0.20V Current: 0.5 mA
Beakers full: 0.25V Current: 0.8 mA
Anode: Zinc
Cathode: Copper
The salt bridge allows migration of ions into each beaker (cations into cathode solution and vice
versa) to neutralise charge buildup and maintain cell voltage.
A larger volume of electrolyte solution means a large surface area of electrolyte in contact with
electrodes. This increases the rate at which charged particles are removed from the electrodes,
decreasing the internal resistance and thus the current. However, the voltage within the cell is
caused by the intrinsic properties of the electrodes (difference in electronegativity), and thus is not
Chem notes David Lee BHHS 2007 22
altered significantly. It is affected slightly since a charge buildup generates a slight back emf, which
reduces the voltage, and more electrolyte action reduces this. Note: Concentration of electrolyte
does affect voltage.
The current output needs to be measured quickly since the ions in salt bridge are being used up, and
charge begins to build in half-cells opposing current flow.
Sources of error:
Electrodes not completely polished – reduces effective surface area of action for electrolyte and
thus current
Method B:
1). The copper half-cell in A was set up
2). Another half-cell consisting of a magnesium strip in magnesium sulfate solution was set up
3). The electrodes were connected to the terminals of a voltmeter, and voltage reading recorded
4). Steps 2-3 were repeated with:
a. Aluminium in 1M aluminium nitrate solution
b. Tin strip in tin(II) nitrate solution
Results:
Test Half-cell Polarity (relative to Total cell voltage
Cu/Cu2+)
Zn/Zn2+ -ve 0.50
Mg/Mg2+ -ve 1.1
2+
Sn/Sn -ve 0.35
Al/Al3+ -ve 0.90
Standard potential Cu – +0.34 V (Oxidation potential -0.34V)
Half Reaction (write in Predicted voltage E0 (V) Experimental E0 (V)
during exam)
Zn -0.76 -0.16
Mg -2.36 -0.76
Al -1.68 -0.56
Sn -0.14 -0.01
The more active the metal, the greater the potential difference.
Note: Oxidation potential is the ability of a substance to oxidise in relation to hydrogen, reductional
potential is ability to reduce in relation to hydrogen. E.g. Copper has reduction 0.34 meaning it has
higher ability to reduce, but its oxidation is -0.34, it has less ability to oxidise.
• Gather and present information on the structure and chemistry of a dry cell or lead-acid
cell and evaluate it in comparison to one of the following:
o Button cell (Silver Oxide cell)
In terms of:
o Chemistry
o Cost and practicality
o Impact on society
o Environmental impact
Criteria Dry Cell (Leclanche Cell) Button Cell (Silver Oxide Cell)
• Distinguish between stable and radioactive isotopes and describe conditions under which
a nucleus is unstable
Zone of stability:
Transuranic elements are elements with atomic number above Uranium (92)
o Some isotopes undergo fission when bombarded, others undergo nuclear reactions to
form new elements
o When non-fissionable atoms such as Uranium 238 are bombarded with high speed
particles, it absorbs the particle to become an unstable atom
o It then rapidly decays to form a new element
There are two machines that are used to produce high speed positive particles to produce
transuranics.
They can also be produced in nuclear reactors, a source of neutrons. Neutrons do not experience
electric repulsion like positive nuclei, and thus speeds in nuclear reactors are adequate. These create
transuranic elements with a proton deficiency.
e.g.
238 1
→ 239
92 U + 0 n 92 U →−10 e+ 239
93 Np
Unstable
238 12
→250
92 U + 6 C 98 Cf → 246
1
98 Cf + 4 0 n( )
23 transuranic elements have been created thus far.
Note these elements are temporarily using IUPAC systematic element names, before they are
officially named.
o Scintillation counter – ionizing radiation hits the scintillation crystal (depicted), the
electrons are excited and emit photons which can be detected and amplified by a
photomultiplier tube (depicted) to produce a reading.
Currently operating in Australia for this purpose is HIFAR reactor, managed by ANSTO
e.g.
Creation of technetium:
98 1 99
42 Mo + 0 n
→ 42 →9943
Mo m
Tc + −10β
Technetium decays, releasing gamma ray inside body
Iodine-131 –
Produced in cyclotron or nuclear reactor, testing of thyroid function and treatment of thyroid
ailments such as overactive thyroid or thyroid cancer (beta decay destroys some thyroid cells)
o Iodine-131 is naturally absorbed by cells in the thyroid gland
o Relatively short half life to minimise exposure (8 days)
Specific problems:
o Ionising radiation of iodine-131 deals collateral damage to other cells
o Radiation penetrates the body and can damage organic tissue near to the patient
o Transport and production in nuclear reactors requires stringent safeguards, which is
problematic
Cobalt-60 – used to measure thickness of materials. With fixed geometry for source and detector,
penetration of radiation emitted from radioisotope (beta particles in this case) determines thickness
of material. Gamma ray producer
o Long half-life so does not need to be replaced frequently (5.3 years)
o Low energy emissions, so absorption is significant and can be detected
o Low energy emissions, minimises safety procedures required
Sodium-24
Used to detect leaks in water pipes or underground oil pipes. Dissolved into water source, can be
subsequently detected in soil around areas of leakage.
o Dissolves easily into water
o Relatively short half-life to minimise environmental damage (15 hours)
• Use available evidence to analyse benefits and problems associated with the use of
radioactive isotopes in identified industries and medicine
Benefits in medicine:
o Created wide range of non-invasive diagnostic procedures otherwise impossible, such as
technetium-99m used to identify brain tumours, gallium-67 for cancers, an area very
dangerous for surgery
o Allowed radiation therapy to treat many forms of cancer, e.g. iodine-131 for treatment of
thyroid cancer
Benefits in industry:
Problems:
o Exposure of radiation doses to workers in medicine, industry and research can damage
tissues e.g. ionizing radiation of sodium-24 causes cancer by removing electrons from the
biological molecule DNA.
o Extra safety precautions are required for sites with radioactive materials, such as proper
storage facilities and protective clothing e.g. industries dealing with cobalt-60 and
technetium-99m need to filter out the fine radioactive dust produced, which can pose a
lung cancer risk
o Disposal of radioactive waste requires space, and can be problematic since isotopes such
as Cobalt-60 remain radioactive a long time after they are no longer useful, may leak into
environment without strict procedures
Acids and bases react to form salt and water (there are exceptions). Note that the salt is in aqueous
solution, separated as ions and not precipitated. E.g. reaction of sodium hydroxide with
hydrochloric acid:
Acidic:
Vinegar (acetic acid) – used in cooking (~3)
Lemon juice (citric acid) (~2.5)
Vitamin C (ascorbic acid) – vitamin supplement
Hydrochloric acid – pH maintenance in swimming pools, clean bricks cement and tiles (~1)
Neutral:
Water
Salts (e.g. sodium chloride, copper sulfate)
Milk
Basic:
Baking soda (sodium bicarbonate) (NaHCO3) (~8.5)
Oven and drain cleaners (sodium hydroxide) – sodium hydroxide also used in soap, and alumina (~
13)
Lime (calcium hydroxide) – making mortar (~ 11)
Ammonia – used to make fertilisers (~ 12)
• Identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol
blue can be used to determine the acidic or basic nature of a material over a range, and
that the range is identified by change in indicator colour
• Identify data and choose resources to gather information about the colour changes of a
range of indicators
An indicator is a substance that in solution changes colour depending on the pH of the solution.
There are many different indicators, and the range of pH over which these indicators change colour
varies. Litmus is the most common and is extracted from lichens. The indicator changes colour in
reaction with the pH of a substance, indicating acidity or basicity dependant on the range of the
indicator.
Universal indicator is a mixture of several indicators and works over the whole range
• Identify and describe some everyday uses of indicators including the testing of soil
acidity/basicity
o Testing home swimming pools which need to be neutral. Acidic water burns eyes,
alkaline water causes skin rashes. Operation of electrochemical cell to produce chlorine
makes pool more alkaline. A pool sample is collected into a vial and an indicator, usually
phenol red (yellow -> red) (6.6 – 8.0) is added and compared to a colour chart. HCl
added if too basic.
o Monitoring wastes from laboratories that process photographic film, as photographic
solutions are highly alkaline and discharges need to be neutral in order to not adversely
affect the environment
o pH in aquariums – fish excrete ammonia which reacts with water, making it more basic.
Universal indicator is used
Method:
1). A handful of shredded red cabbage was boiled in water over a bunsen burner for about 5 minutes
2). The resulting liquid solution was poured into a filter paper/filter funnel apparatus and collected
in a beaker
3). 20 mL of 1 M HCl solution was poured into a measuring cylinder
4). 10 mL was poured into a small test tube which was labelled ‘0’
5). The remaining 10 mL was poured into a beaker and diluted to 100 mL
6). 20 mL of the resulting solution was poured back into the measuring cylinder, and steps 4 – 5
were repeated 5 times, each test tube being labelled a successive integer higher
7). Steps 3-6 were repeated starting with 1 M NaOH solution and labelling from 14 down
8). A few drops of red cabbage indicator were added to each test tube and observations recorded
Results:
Red (0-1) Pink (2) Purple (3-4) Clear (5-6) Purple (7-9) Blue (10-11) Green (12-
13) Yellow (14)
There are 6 discrete colour stages for this indicator. This suggests multiple molecules within the red
cabbage indicator solution acting to produce colour changes. Each molecule has a specific colour
when a proton is added or taken away. The molecules in this case are anthocyanins, and there are
about 15 different ones in red cabbage indicator.
• Solve problems by applying information about the colour changes of indicators to classify
some household substances as acidic, neutral or basic
• Identify oxides of non-metals which act as acids and describe the conditions under which
they act as acids
An acidic oxide is one which either reacts with water to form an acid, or reacts with bases to form
salts (or both). E.g. carbon dioxide and diphosphorous pentoxide P2O5
The latter is more correct, as the acidic oxide would react with water to form the acid first. It would
depend on the relative concentrations of the oxide and the acid in solution, as it is an equilibrium
reaction. However, since both create the same products, this is negligible.
And similarly for P2O5
A basic oxide show basic character, and react with acids to form salts, but not with alkali solutions
e.g.
Amphoteric oxides are those showing both acidic and basic character, and those that react with
neither acids or bases are neutral oxides e.g. NO, CO, N2O
• Analyse the positions of these metals in the periodic table and outline the relationships
between position and acidity/basicity of oxides
If a system in equilibrium is disturbed, then the system adjusts itself so as to minimise the
disturbance
Reversible reactions occur when products can react to generate reactants. When a reaction starts,
forward reaction generates products from reactants. Backward reaction then generates products,
Chem notes David Lee BHHS 2007 32
which form at an increasing rate as product concentration increases. The equilibrium occurs at the
point where formation of products is equal to the rate of reactant formation, no net change in
concentration.
Factors:
o Concentration species – increasing/decreasing concentration of a species will cause
reaction equilibrium to shift so that it decreases/increases the species concentration. This
because it naturally results in more/less collisions or more/less decomposition to form
more/less of that chemical. Note that reactions involving solids and liquids experience
little effect, as concentrations remain almost unchanged (note: this does not include
dissolved substances).
o Pressure in a gaseous reaction – an increase/decrease will cause a increase/decrease in
concentration (and vice versa for volume). Depending on which side of the reaction has
more particles, the equilibrium will shift in that direction in order to reduce number of
particles and thus pressure (or vice versa). Note that increasing reaction by increasing
concentration of gas not involved in reaction e.g. argon has no effect
o Temperature – If the temperature is lowered, the amount of energy in the system
decreases and the exothermic reaction is favoured since less particles have sufficient
energy to form products with a higher potential energy. And vice versa
o Catalysts – increases speed at which equilibrium is reached, does not alter equilibrium
position as activation energy of both product and reactants formation is decreased
Notable exceptions:
o When solid or liquid is involved in reaction – the concentration of these substances stays
constant
o The addition of water to an aqueous reaction involving water – concentration of water
does not change significantly, but other substances more dilute
Discussion:
The dissolution and reaction of CO2 in water is multistep equilibria –
CO2(g) CO2(aq) … (1)
CO2(aq) + H2O(l) H2CO3(aq) … (2)
H2CO3(aq) + H2O(l) HCO3-(aq) + H3O+(aq) … (3)
HCO3-(aq) + H2O(l) CO32-(aq) + H3O+(aq) … (4)
Factors:
• Identify natural and industrial sources of sulfur dioxide and oxides of nitrogen
• Describe, using equations, examples of chemical reactions which release sulfur dioxide
and chemical reactions which release oxides of nitrogen
o Extraction of metal from sulfide ores – first step is to roast sulfide ore in air e.g.
extraction of zinc roasting zinc sulfide
2ZnS(s) + 3O2(g) -> 2ZnO(s) + 2SO2(g)
Industrial sources:
Nitrogen dioxide and sulfur dioxide are washed out by rain, so there is no significant buildup in
atmosphere. Nitrous oxide however, has steadily increased by about 15%, from measurements made
over the last century. There are problems associated with collecting evidence for sulfur and nitrogen
oxides, namely:
o Concentrations of both are very low, below 0.1ppm, and only recently (since about the
1950’s) are instruments accurate enough to reliably measure the levels, so trends before
this period could be invalid
o Sulfur dioxide and nitrogen dioxide form sulfate and nitrate ions which are changed
chemically as they move around the hydrosphere, so measuring traces of these
compounds is difficult
Most evidence comes from observed occurrences such as acid rain. There appears to be an increase
from data but it is inconclusive due to lack of long-term trends and inaccuracies of earlier
measurements.
• Analyse information to summarise the industrial origins of sulfur dioxide and oxides of
nitrogen and evaluate reasons for concern about their release into the environment
Concern about release into environment because it has detrimental effect on environment and can
cause harm to people since:
Sulfur dioxide:
o Sulfur dioxide irritates the respiratory tract, and can cause symptoms in people with
asthma or emphysema in concentrations as low as 1ppm
o Forms acid rain
o Dry deposition causing environmental damage
Nitrogen oxides:
o Nitrogen dioxide irritates the respiratory tract, and can cause extensive tissue damage in
concentrations 3-5 ppm
o The action of sunlight on nitrogen dioxide, hydrocarbons and oxygen increases
photochemical smog, which includes ozone – poisonous substance
o NO and NO2 participate in ozone layer depletion (NO + O3 NO2 + O2)
o Forms acid rain
o Contributes to global warming
o Sulfur dioxide and nitrogen dioxide gases released dissolve in water to form sulfuric acid
and nitric acid which is washed out of the atmosphere by rain, forming wet deposition
acid rain.
Reaction with hydroxyl radicals:
SO2(g) + 2OH H2SO4(aq)
(OR)
(OR)
Dry formation:
Incorporated into dust and smoke and falls to the ground
• Increased acidity of lakes, killing aquatic life e.g. snails can only tolerate up to pH
6.0
• Mobilisation of Al3+ ions in soil due to reduced pH. This flows into lakes and
precipitates out, clogging fish gills and suffocating them
• Calculate volumes of gases given masses of some substances in reactions, and calculate
masses of substances given gaseous volumes, in reactions involving gases at OoC, 100 kPa
or 25oC and 100kPa
Equal numbers of molecules of different gases occupy the same volume in isothermal and isobaric
conditions. At 0oC and 100 kPa, 22.71 L per mole and 24.79 L/mol for the other.
• Gather and process information to write the ionic equations to represent the ionisation of
acids
• Define acids as proton donors and describe the ionisation of acids in water
Acids react with water in solution to form a solution containing hydronium ions and its conjugate
base.
• Describe acids and their solutions with the appropriate terms weak, strong, concentrated
and dilute
• Describe the difference between a strong and weak acid in terms of an equilibrium
between intact molecules and its ions
A strong acid is one in which all acid present in solution has ionised to hydrogen ions (no degrees
of strength), no equilibrium is formed. A weak acid is one in which only some of acid molecules
present in solution have ionised to form hydrogen ions, forming an equilibrium between intact
molecules and ions. The fraction of molecules ionised is called the degree of ionisation
(concentration of H+/concentration of acid originally).
Method:
1). 50mL of 0.1M hydrochloric, acetic, oxalic, citric and sulfuric acid were prepared in labelled 250
mL beakers
2). A pH meter was used in each beaker and the reading recorded
3). A pH strip was placed into each beaker for a short period and its colour compared with a chart
4). A few drops of universal indicator were dropped into each beaker and the colour compared to a
colour chart
Results:
#####
The strongest was sulfuric acid. It is a strong acid and is diprotic, meaning
that the concentration of H3O+ ions is twice the concentration of
hydrochloric acid. HCl is strong but monoprotic, meaning concentration is
identical to HCl concentration. Oxalic acid is diprotic and citric is triprotic,
Chem notes David Lee BHHS 2007 37
but both are weak and do not completely ionise. The tendency for their conjugate bases to re-bond
with hydrogen ions limits the concentration of H3O+ in solution. Acetic is the weakest, being
monoprotic and have a low degree of ionisation.
Oxalic – C2H2O4
Citric – C6H8O7
Acetic/ethanoic – CH3COOH
Safety:
HCl - corrosive, vapour can burn mouth, throat and eyes
Oxalic acid – corrosive to tissue, corrosive to respiratory tract if inhaled
Wear safety glasses, goggles, use lower concentrations and smaller amounts
• Compare the relative strengths of equal concentrations of citric, acetic and hydrochloric
acids and explain in terms of the degree of ionisation of their molecules
HCl is the strongest acid and has the highest degree of ionisation.
• Use available evidence to model the molecule nature of acids and simulate the ionisation
of strong and weak acids
• Gather and process information to explain the use of acids as food additives
• Identify examples of naturally occurring acids and bases and their chemical composition
Acids:
o Ascorbic acid C6H8O6 – occurs widely in fruit and vegetables, essential to health
o Citric acid – found in citrus fruits
o Lactic acid CH3CH(OH)CO2H – produced by anaerobic respiration in cells, found in
muscle tissue and milk
o HCl – stomach to break down food
Bases:
o Ammonia NH3 – result of decomposition of proteins, or anaerobic decay of organic
matter found in fish urine
Chem notes David Lee BHHS 2007 38
o Carbonates – e.g. calcium carbonate (limestone), magnesium carbonate
o Metallic oxides – e.g. Iron (III) oxide, copper oxide and titanium oxide, found in
minerals. Metals are extracted from them.
• Outline the historical development of ideas about acids including those of:
o Lavoisier
o Davy
o Arrhenius
o Lavoisier (1780)
• acids were substances that contained oxygen
• Disproved since some oxygen-containing compounds such as metallic oxides were
basic, and distinctly acidic substances such as hydrochloric acid contained no oxygen
• Wrong but stimulated research
o Davy (1815)
• suggested that acids were substances that contained replaceable hydrogen.
• Bases were substances that reacted with acids to form salt and water.
• These definitions worked well for most of that century, but the definition made no
attempt to interpret the properties, only classify the substances
o Arrhenius (1884)
• Interpreted acidic properties in terms of ionisation to form H+, and weak/strong in
terms of degrees of ionisation
• the conductivity of acid solutions and their reaction with many metals to form
hydrogen gas evidenced that acidic solutions contained hydrogen ions
• acids were substances that ionised in solution to produce hydrogen ions
• A base is a substance that in solution produced hydroxide ions
• He defined strong acids as those that ionised completely and weak as those that
partially ionised. General equations:
HA(aq) H+(aq) + A-(aq)
XOH(aq) X+(aq) + OH-(aq)
Weaknesses were:
Does not take into account role of solvent in ionisation of acid (ionisation
results from reaction of acid with solvent)
Acid-base reactions can occur in solvents where there is no ionisation
Not all acidic/basic substances (e.g. metallic oxides) ionised to produce
hydrogen/hydroxide ions
An acid is a proton donor, a base is a proton acceptor. Gives the broadest definition of acid/base
theory (it means that acids must have hydrogen). This definition :
o Does not restrict bases to those which ionise to produce hydroxide ions, such as in the
case of metal oxides and ammonia
o Explains how neutralisation reactions don’t require dissolution of ions into aqueous
solution e.g. NH3 + HCl in benzene (direct proton transfer)
o Exchange of proton relies on relative properties of both substances involved, accounting
for the role of the solvent
o Shows that hydrolysis of salts to change pH were acid or base reactions
o Provided basis for quantitative treatment of acid-base equilibria and pH calculations
• Describe the relationship between an acid and its conjugate base and a base and its
conjugate acid
When an acid loses a proton, the resulting ion is called a conjugate base. If the acid is not strong,
this conjugate base can re-take a proton to reform the acid, resulting in an equilibrium reaction.
Vice versa for bases
• Identify a range of salts which form acidic, basic, or neutral solutions and explain their
nature
A salt is an ionic compound containing a cation not H+ and an anion not O2- or OH-. In aqueous
solution, salts completely dissociate into ions.
Type Acidic Basic Neutral
Salt Ammonium nitrate Sodium acetate Sodium chloride
(NH4NO3) (NaCH3COO) Potassium nitrate
Sodium hydrogen Potassium nitrite (KNO3)
sulfate (NaHSO4) (KNO2) Sodium sulfate
Anything Sodium carbonate (Na2SO4)
3+
containing Al , (Na2CO3)
Fe3+, HSO4- or Anything
-
H2PO4 containing F-, S2-
etc.
The pH of a salt solution depends on the nature of its ions, many cations/anions serve as acids or
bases. Some generalisations:
o Neutral salts have anions which are the conjugate base of strong acids, and cations the
conjugate acid of strong bases, since their reaction to accept/give protons is negligible
o Basic anions react with water to form hydroxide ions in solution. Reaction is equilibrium,
occurs to small extent since conjugate acid is stronger than water, and conjugate base is
stronger than basic anion
o Acid anions contain hydrogen atoms to react with water to form hydronium ions, derived
from polyprotic acids. The anion resulting from hydrolysis of polyprotic acids is
amphiprotic, and whether it is acidic or basic depends on the tendency for one hydrolysis
reaction (proton donation or proton accept) to occur over the other
Some examples:
(Basic anions)
S2–(aq) + H2O(l) ↔ HS–(aq) + OH–(aq)
F–(aq) + H2O(l) ↔ HF(aq) + OH–(aq)
(Acidic cations)
[Fe(H2O)6]3+(aq) + H2O(l) ↔ [Fe(OH)(H2O)5]2+(aq) + H3O+(aq)
Self explanatory. You could use NaCl + KOH for neutral, sodium bicarbonate (NaHCO3) and
sodium acetate (NaCH3COO) for basic, ammonium chloride (NH4Cl) for acidic.
Amphiprotic substances can act as both a proton donor and proton acceptor. They react to both
accept protons and donate protons. Their behaviour changes whether in aqueous solution or
alkaline/acid solution.
In basic/acidic solution:
HCO3-(aq or s) + OH- H2O(l) + CO32-(aq)
HCO3-(aq or s) + H+(aq) H2CO3(aq)
Reactions go to completion since products cannot perform the reverse reaction (???). This also
applies to HSO3- (hydrogen sulfite) and HSO4-. Water is amphiprotic.
Neutralisation reactions are proton transfer reactions, and involve the reaction between an acid and
a base. They are exothermic and thus have a negative enthalpy change. The net ionic reaction in
Arrhenius theory is:
Acids and bases not fitting in Arrhenius theory do not necessarily produce salt and water during
neutralisation reactions e.g. neutralisation of ammonia. In LB theory, an acid and base react to form
conjugate base and conjugate acid. The acid gives a proton to the base. Reactions between strong
acids and bases form very weak conjugate acids/bases and go virtually to completion since the back
reaction has almost no tendency to occur. Otherwise, reactions are equilibria.
Chem notes David Lee BHHS 2007 41
• Describe the correct technique for conducting titrations and preparation of standard
solutions
Determining the composition of a solution require titration against another solution of known
concentration, called the standard solution. The substance dissolved is a primary standard.
Equipment:
A primary standard:
o Must be obtainable in very pure form and have known formula
o Should not alter weight unintentionally during preparation/titration e.g. absorbing
moisture from air
o Have a reasonably high formula mass to minimise weighting errors
o Purified by drying in oven and cooling in dessicator to eliminate moisture and prevent its
absorption
e.g. oxalic acid, sodium carbonate
Use of equipment:
o Pipette – solution to be used is first drawn in above mark, then solution let out until
meniscus at mark, solution let out through gravity with tip against wall of container
o Burette – first, rinse with portion of solution to be dispensed, overfilled then excess
allowed to run out
Preparation:
o Accurately measure mass of primary standard e.g. electronic beam balance
o Rinse a volumetric flask and beaker with distilled water
o Pour the primary standard into beaker and dissolve with distilled water, less than
intended volume of final solution
o Pour into volumetric flask, and repeat a few more times
o Use a pipette to add final few drops to complete solution
Titration curves:
Strong acid strong base:
Weak/weak
Not good since gradient around equivalence point is quite shallow, big volume difference between
indicator endpoints and equivalence points, needs to fit indicator very well or use one which
changes during equivalence, hard to distinguish.
• Perform a first-hand investigation and solve problems using titrations and including the
preparation of standard solutions, and use available evidence to quantitatively and
qualitatively describe the reaction between selected acids and bases
Prac – Titration
Aim: To standardise HCl and NaOH solutions using titration
Method:
Preparing standard:
1). A clean 250mL beaker was placed on an electronic balance, zeroed, and had 2.650g of Na2CO3
added using a spatula
2). Approx 100 mL of distilled water was added to the beaker, and solution stirred using stirring rod
3). A 250mL volumetric flask was rinsed with distilled water*
4). The Na2CO3 solution was poured into the volumetric flask, and step 2 repeated
5). The stirring rod/beaker were thoroughly washed using a wash bottle, the runoff dripping into the
vol. flask
6). Using a 25mL pipette, the volumetric flask was filled to the 250mL mark
7). A stopper was placed on the flask and contents swirled to mix
8). The pipette was rinsed with the unknown HCl*
9). 10 mL of unknown concentration HCl was poured using a pipette into a 50mL beaker washed
with distilled water*, and a few drops of methyl orange added
10). A burette was washed and filled with the Na2CO3 standard solution
11). The standard solution was quickly drained into the beaker to find an approximate end point
12). Steps 8-10 were repeated 3 times but more accurately
*
to ensure no cross-contamination
See book for calculations
Buffer solutions resist changes in pH. It contains comparable amounts of a weak acid/base and its
conjugate base/acid. Take for example an acetic acid (CH3COOH) and sodium acetate
(NaCH3COO) system (acidic buffer).
Maintains the blood at around 7.4 for optimum function, too high/low can result in death.
o Many acids and bases are corrosive, can damage materials if spilt
Neutralisation reactions can:
o Reduce or nullify corrosive properties of spill, minimising damage
o Utilise common, cheap, safely handled/stored materials and produces relatively harmless
products e.g. sodium bicarbonate NaHCO3
Sodium bicarbonate is amphiprotic, so it can be used for both acidic and basic spills:
OH − ( aq ) + HCO3 − ( aq )
→ CO3 2− ( aq ) + H 2 O(l )
H + ( aq ) + NaHCO3 ( aq )
→ CO2( g ) + H 2 O(l ) + Na + ( aq )
Vinegar – commonly used in cooking, contains acetic acid:
OH − ( aq ) + CH 3COOH ( aq ) → CH 3COO − ( aq ) + H 2 O(l )
o Degree of reaction can be controlled by using different amounts of neutralising
substance, excessive amounts are wasteful and some
• Describe the differences between the alkanol and alkanoic acid functional groups in
carbon compounds
• Explain the difference in melting point and boiling point caused by straight-chained
alkanoic acid and straight-chained primary alkanol structures
Strong intermolecular forces – higher BP/MP compared to similar mole mass (roughly similar
dispersion forces)
-OH
carboxylic acid group
Forms One hydrogen bond between Two polar bonds between molecules (C-
molecules O polar and C – O – H hydrogen bond),
higher boil/melt point
None ionised, neutral Small no. ionised, acidic
• Identify the IUPAC nomenclature for describing the esters produced by reactions of
straight-chained alkanoic acids from CI to C8 and straight-chained primary alkanols
from C1 to C8
Chem notes David Lee BHHS 2007 44
Alkyl (e.g. methyl) alkanoate (e.g. formate, acetate, propanoate etc.)
• Identify esterification as the reaction between an acid and an alkanol and describe, using
equations, examples of esterification
Standard equation:
H SO
e.g. CH 3COOH (l ) + CH 3OH (l ) ←2
4 → CH 3COOCH 3 (l ) + H 2 O(l )
(acetic acid + methanol)
H 2 SO4
HCOOH (l ) + CH 3CH 2 OH (l ) ← → HCOOCH 2 CH 3 (l ) + H 2 O(l )
(formic acid + ethanol)
o The acid acts as a dehydration agent, removing water from the reaction (Le chatelier
argument), thus increasing yield
o Acts as a catalyst, lowering activation energy to speed reaction
o Only small amounts of acid required
o Most common is sulfuric, others include tosic, scandium (III) triflate
Esters occur naturally, and are identified as fragrances and flavours in fruit and flowers e.g. orange
(octyl acetate). Animal fats such as butter, or oils such as linseed are also esters, as are waxes.
These fats and oils can be used to make soap
(Fat or oil) + sodium hydroxide → Salt of carboxylic acid + glycerol
Ethyl acetate:
o Solvent in industry, nail polish remover
o Acetic acid and ethanol
C2H5OH + CH3COOH → C4H8O2 + H2O
Octyl acetate:
o As a food flavouring such as in sweets, ice cream etc.
o Acetic acid and octanol
C8H17OH + CH3COOH → C10H20O2 + H2O
Prac – Esterification
1). 15 mL of acetic acid, 15 mL of butan-2-ol and 10 drops of conc.
Sulfuric acid was placed into a 100 mL round-bottom flask
2). The apparatus was set up as shown
3). The bunsen burner was lit and reflux allowed to occur for about
15 minutes until two layers clearly visible
4). A separating funnel was assembled on a retort stand and 100 mL
of distilled water poured inside
5). Contents of round-bottom flask were transferred into funnel and
the mixture shaken
6). 50mL of sodium carbonate solution was added and gently
shaken, occasionally inverted and tap opened to release gas
7). Once the layers separated, the lower layer was discarded
8). Step 6-7 was repeated
9). The remaining liquid was poured into a conical flask and a
teaspoon of CaCl2 added, shaken gently then allowed to stand for a
few minutes
Safety:
1). Acetic acid + butan-2-ol flammable, apparatus should be secured to ensure no tipping; tipping
could pose fire risk due to contact with bunsen flame
2). Acetic acid corrosive to skin, avoid spilling
3). Condenser should have adequate water to prevent organic vapour escaping, flammable and
respiratory irritant
• Outline the role of a chemist employed in a named industry or enterprise, identifying the
branch of chemistry undertaken by the chemist and explaining a chemical principle that
the chemist uses
• Gather, process and present information from secondary sources about the work of
practising scientists identifying:
o The variety of chemical occupations
o A specific chemical occupation for a more detailed study
Many areas a chemist can work in, 13 divisions recognised by Royal Australian Chemical institute
including:
o Environmental chemistry (detailed) – determining how substances interact in the
environment, monitoring concentrations of substances especially in air, water and soil
Environment monitoring, employed by Environmental Protection
Authority, mining companies, local government – qualification can be BSc
and postgrad qualification in fields such as scientific
communication/management. Could collect data on air/water quality, then
analyse and assess this information. Require strength in chemical analysis,
and instrumental analysis. May work in a team, providing environmental
advice to external bodies via reports.
o Physical chemistry – study and measurements of physical aspects of compounds and
reactions e.g. reaction rates, structure of substances, nature of chemical bonding
• Identify the need for collaboration between chemists as they collect and analyse data
2CO( g ) + O2( g )
→ 2CO2( g )
o Sulfur oxides – some sulfur compounds in fuels:
S ( 2 ) + O2 ( g )
→ SO2 ( g )
2 S ( s ) + 3O2( g )
→ SO3( g )
Monitoring can ensure minimum possible toxic chemicals released, important since:
o CO affects judgement/perception as levels as low as 10 ppm, can cause death by
asphyxiation
o Soot contributes to particulate pollution, bad for asthma sufferers
o Nitric oxide affects respiratory systems and is generally toxic, excessive production by
motor vehicles can affect health of population
o Sulfur oxides and nitric oxides contribute to acid rain
o Motor industry can use information to build more efficient engines (more complete
combustion)
• Identify that ammonia can be synthesised from its component gases, nitrogen and
hydrogen
• Describe that synthesis of ammonia occurs as a reversible reaction that will reach
equilibrium
• Identify the reaction of hydrogen with nitrogen as exothermic
• Explain why the rate of reaction is increased by higher temperatures
• Explain why the yield of product in the Haber process is reduced at higher temperatures
using Le Chatelier’s principle
• Analyse the impact of increased pressure on the system involved in the Haber process
• Explain that the use of a catalyst will lower the reaction temperature required and
identify the catalyst(s) used in the Haber process
Nitrogen and hydrogen combine to form ammonia, which in turn decomposes to reform reactants
(reversible reaction). Equilibrium reached when rate of forward/reverse reactions the same.
At higher temperatures, the average kinetic energy of the reactants is higher. Thus:
1. Larger fraction of molecules have adequate energy to overcome activation energy and react
upon collision
2. Molecules move faster, more collisions between molecules
These increase the rate of reaction, and apply to both forward and backward reactions. However, it
affects forward reaction more.
Reaction is exothermic, higher temperatures shifts equilibrium to left to reduce temperature change.
Number of moles of gas on each side of reaction is different. According to Le Chatelier’s principle,
increasing pressure shifts equilibrium to right since there are less moles of gas, decreasing pressure
and thus minimising pressure change. Vice versa
• Explain why the Haber process is based on a delicate balancing act involving reaction
energy, reaction rate and equilibrium
Balancing these factors to maximise yield and reaction rate is required to maintain adequate
production and use of resources:
• Explain why monitoring of the reaction vessel used in the Haber process is crucial and
discuss the monitoring required
o Temperature and pressure of reaction vessel – keep within range for optimum
production rate, excess temperatures can damage catalyst and lower yield
o Ratio of incoming reactants – maintain stoichiometric ratio and prevent buildup of one
reactant, slowing reaction
o Impurities in incoming gases – O2 can cause explosion, CO/CO2 can poison catalyst
and reduce its lifespan
o Rate of ammonia removal – inadequate rate of removal shifts equilibrium to reactants,
reducing yield
• Describe the conditions under which Haber developed the industrial synthesis of
ammonia and evaluate its significance in that time in world history
• Deduce ions present in a sample from a range of tests (Maybe need mixtures – go to
conquering chem for good summary)
Cations:
Cations:
Confirmation tests:
Ba2+ - apple green flame
1
CO32-(aq) + 2H+(aq) CO2(g) + H2O(l)
*
Sulfate weaker lewis base than phosphate
SO42-(aq) + H3O+ HSO4-(aq) + H2O(l), equilibrium enough to left so adequate sulfate to produce
noticeable precipitation with barium/lead (CHECK – how would this effect lead?)
In basic conditions, enough phosphate for precipitation
2
12(NH4)3MoO4 + PO43- + 3H+ (NH4)3PMo12O40
• Describe and explain the evidence for the need to monitor levels of one of the above ions
in substances used in society
• Perform first hand investigations to measure the sulfate content of lawn fertiliser and
explain the chemistry involved
• Analyse information to evaluate the results of the above investigation and to propose
solutions to problems encountered in the procedure
Results
Mass of ammonium sulfate: 1.000
Mass of BaSO4 precipitate: 0.655 g
96.06
Mass of SO42- = x0.655 = 0.270 g
233.36
• Describe the use of AAS in detecting concentrations of metal ions in solutions and assess
its impact on scientific understanding of the effects of trace elements
• Interpret secondary data from AAS measurements and evaluate the effectiveness of this
in pollution control
Atomic absorption spectroscopy – used to measure low concentrations of elements in ppm range,
mainly metals.
Each element has unique emission spectrum, so by measuring, studying and using spectra we can
determine qualitatively and quantitatively the elements present in sample (by looking at spectra,
measuring intensity)
Why useful:
o Relies on absorption rather than emission, nearly 100% atoms in ground state absorb as
opposed to <0.1% excited which emit, can measure down to ppb
o Can measure concentration of only one element at a time
Uses:
Layer of gas about 200 – 300 km thick surrounding the earth. Many different gases and distinct
layers which different characteristics:
Overall gas composition: 78% N2, 21% O2, 0.93% argon, trace amounts of CO2, neon, methane etc.
Layer Altitude above Most common gases Description
surface (km)
Troposphere 0 – 15 N2, O2, H2O, CO2, Ar Contains most of earth’s gases,
organisms inhabit this zone,
weather events
Stratosphere 15 – 50 N2, O2, O3, Contains ozone layer (25 km),
temperature increases with
altitude and gives stability
Mesosphere 50 – 80 Coldest layer (down to -100
celsius)
Thermosphere/ >80 Ions (O2+, NO+), O Temp rises with altitude, ionic
Ionosphere and atomic gas particles,
important in radio
communications since radio
waves reflect off
• Identify the main pollutants found in the lower atmosphere and their sources
Pollutant Source
CO Burning fossil fuels, forest fires
Airborne lead Lead smelters, leaded fuels
CFC’s Foaming agent, refrigerant-air conditioner coolant,
propellant
SO2 Combustion (fuel impurities), metal extraction from
sulfide ores, chemical manufacturing
Chem notes David Lee BHHS 2007 54
Oxides of nitrogen (NO + Combustion (vehicles and power stations)
NO2)
Particulates Combustion, bush fires, industrial processes such as
mining
Allotrope – a different physical form of the same element in the same phase
Ozone is:
o An allotrope of element oxygen
o Naturally present in atmosphere; only 0.02 ppm at ground level in clean air, 2 – 8 ppm in
stratosphere
o Detrimental in lower atmosphere – poisonous to many organisms; causes breathing
difficulties, fatigue and headache in humans
o Beneficial in upper atmosphere - filters our short wavelength UV light which can damage
living tissue
Coordinate covalent bonds occur when shared the electrons come from one atom. Once formed,
identical to regular covalent bond.
• Compare the properties of the oxygen allotropes O2 and O3 and account for them on the
basis of molecule structure and bonding
Property O2 O3 Reason
Boiling point -193 -111 Polar bonds between
(oC) molecules means
intermolecular forces
stronger (O3)
Odour None Sharp, irritating
Colour None Pale blue
Density Slightly denser than 1.5 times denser than One more O atom per
air air molecule
Reactivity Highly reactive with Very highly reactive, The O-O bonds in O3
many metals and non- attacks double bonds are less strong than the
metals on alkenes double covalent bond
in oxygen
Solubility in Sparingly soluble More soluble than O2 O2 is non-polar, O3 is
water bent and thus is polar
Oxidation Lower Higher O involved only in
ability coordinate covalent
has greater electron
affinity
Free radical – a neutral species with an unpaired electron which can be formed by splitting a
molecule into two neutral fragments
Property O2 O
Reactivity Less reactive (full outer Very reactive (unpaired electron)
valence shell)
Oxidation Lower Higher (unpaired electron, high
ability tendency to take electrons to
complete valence shell)
• Identify and name examples of isomers (excluding geometric and optical) of haloalkanes
up to eight carbon atoms
• Model isomers of haloalkanes using model kits
Haloalkane – hydrocarbon with one or more hydrogens replaced by halogen atoms (encompass
CFC’s)
• Discuss the problems associated with the use of CFC’s and assess the effectiveness of
steps taken to alleviate the problem
• Write the equations to show the reactions involving CFC’s and ozone to demonstrate the
removal of ozone from the atmosphere
• Identify alternative chemicals used to replace CFC’s and evaluate the effectiveness of
their use as a replacement for CFC’s
Problems:
Removal of stratospheric ozone
o CFC’s released into the troposphere are not washed out by rain (non-soluble) and not
destroyed by sunlight/oxygen at low altitudes
o Diffuse into the stratosphere and short wavelength UV breaks a chlorine off e.g.
CCl 3 F +UV
→Cl • +CCl 2 F
o Chlorine reacts with ozone
Cl + O3
→ •ClO + O2
o ClO reacts with free oxygen atoms
ClO + O
→ •Cl + O2
o Net result is conversion of O3 and O to two O2
o Chlorine molecule unchanged at end, can continue to react and remove ozone
o This occurs on average a few thousand time before chlorine radical reacts with another
chemical which removes it e.g. methane
Cl + CH 4
→ HCl + •CH 3
Alleviation:
o Agreements to phase out use of CFC’s (e.g. Montreal Protocol, cease use in developed
by 1996)
o Agreements to phase out use of halons by 2010
o Assistance to poorer countries to phase out CFC use
o Replacement with safer alternatives
HCFC’s – contain C-H bonds decomposable by radicals and atoms in
troposphere and are decomposed to significant extend. However, ozone-
destroying capacity is still significant (phase out by 2030 – Montreal
Protocol). Only useful as temporary substitute
HFC’s – no C-Cl bonds, do not form Cl atoms in atmosphere, no ozone-
destroying capacity. Useful as permanent substitute, but more expensive
Air being used to replace as foaming agent
Assessment:
o Adherence to agreements will ensure ozone layer returns to pre-CFC state since damage
is reversible
o The pace of CFC withdrawal means it will be many decades before the above happens,
meaning the effects of increased UV radiation will be felt
o Relies on co-operation of countries, will be less effective if countries withdraw
o Replacements such as HFC’s are more expensive than CFC’s, may be a burden on lower
countries until better alternatives found
Overall, it is an effective long-term solution but prolongs problems in the short term. It relies
heavily on cooperation of countries and this may be a downfall.
Evidence/information CHECK:
o Measurements of total ozone in a column of atmosphere have been conducted since 1957
o In springtime of 1980-1984, a severe depletion of ozone above Antarctica was detected
by the British Antarctic survey
o By 1985 it was approximately 30%, and in some places it had been completely destroyed
o A net decrease of 3% per decade was recorded for the period 1978-1991, factoring in
natural variations
Method of collection:
Data collected by range of ground and airborne instruments
o Dobson spectrophotometer (up to 48 km, groundbased)
Developed in 1924, only source of long-term data
Water quality is the chemical, physical and biological characteristics of water, with respect to its
intended purpose.
o Hardness
1. Concentration of Ca2+ and Mg2+ ions in water (ppm CaCO3)
2. Hard water forms a precipitate with soap, reducing cleaning power. Under high
temperatures such as in kettles, Ca2+ forms an insoluble precipitate with sulfate
and carbonate ions, reducing kettle efficiency
3. (see below)
4.
a. Titration with EDTA, which forms stable complexes with these ions.
Indicator Eriochrome Black T. In solution is blue but forms red coloured
complex with Mg2+. Endpoint when it turns blue, indicating no more Mg2+
in solution
o Turbidity
1. Measure of suspended solids in water
2. Undesirable appearance and taste, reduces sunlight penetration for plant
photosynthesis, can absorb IR and raise water temperature
3. Clay, silt, plankton, industrial wastes
4. Secchi disk, visually
o Acidity
1. pH of water
2. At extreme ranges, it can reduce survivability for aquatic organisms
3. Decomposition of organic matter, acid rain, exposure of sulfide ores in mining,
fertiliser run-off
4.
a. Universal indicator solution or paper
b. pH meter
• Identify factors that affect the concentrations of a range of ions in solution in natural
bodies of water such as rivers and oceans
o Pathway from rain to water body – rainwater collects ions before it runs into natural
bodies of water
• Bushland contains small amounts of nitrates and phosphates from natural nutrients on
surface
• Rainwater soaking into ground collects Ca2+, Mg2+, sulfate and chloride from soil and
rocks it flows through
• Percolation into deep underground aquifers results in collection of Fe3+, Mn2+ among
others
o Human activity
• Removal of natural vegetation or irrigation can increase salinity and thus NaCl in
rivers
• Agricultural fertilisers contribute nitrates and phosphates through runoff or dumping
• Discharge of sewage increases nitrates/phosphates, and various ions such as Cl-
• Acid rain caused by industry is better able to leech certain cations e.g. Ca2+ and Mg2+
from soil
• Motor car emission can increase lead
o Frequency of rain – more rain means more dissolved ions entering water bodies
o Bushfires – bushfires unlock nutrients and ions such as nitrates from plants, water picks
this during runoff
o Water temperature – higher water temperature increases evaporation and thus increases
concentrations of all ions in solution
• Perform first-hand investigations to use qualitative and quantitative tests to analyse and
compare the quality of water samples
Results:
Results/Analysis
4 Mn2+(aq) + O2(aq) + 8OH-(aq) 2Mn2O3(s) + 4H2O (brown ppt)
Upon addition of acid
Mn2O3(s) + 6H+(aq) 2Mn3+(aq) + 3H2O(l)
2Mn3+(aq) + 2I-(aq) I2(aq) + 2Mn2+(aq)
Redox titration:
I2(aq) + 2S2O32- -- (starch indicator) 2I-(aq) + S4O62-(aq)
Overall reaction:
O2(aq) + 4S2O32-(aq)+ 4H+(aq) 2S4O62-(aq) + 2H2O(l)
Creek Tap
2-
Vol. of S2O3 titrated (ml) 17.4 17.6
[DO]mg/L, % saturation 0.1698 (90.79) 9.2752 (91.83)
• Gather, process and present information on the range and chemistry of the tests used to:
o Identify heavy metals
o Monitor possible eutrophication of waterways
Heavy metals are transition metals plus lead which can be toxic to humans if ingested in higher
concentrations
Chemistry:
o In solution, sulfide and hydronium react according to:
S 2− ( aq ) + 2 H 3O + ( aq ) ←→ H 2 S ( aq ) + 2 H 2 O(l )
When acidified, reaction proceeds enough to right for only minute concentrations of
sulfide left in solution
o Sparingly soluble ions such as lead can precipitate, while others such as zinc cannot
o Non-precipitation eliminates presence of these sparingly soluble ions
o In alkaline solution, enough sulfide remains to cause noticeable precipitation of ions such
as zinc and iron
o AAS
Eutrophication is the enrichment of water bodies by nutrients such as phosphate and nitrate in
excessive amounts (from agriculture, environment or discharged effluents which are decomposed
by aerobic bacteria), leading to algal blooms. This increases the BOD and decreases DO, reducing
survivability of aquatic life. Algal blooms block out sunlight for plant photosynthesis, further
reducing DO and aquatic life. Also develops unpleasant smells and unsightly appearance.
• Describe and assess the effectiveness of methods used to purify and sanitise mass water
supplies
At the catchment:
o Preservation of natural environment – activities such as land clearing and
development cause increased TDS and turbidity; these activities prohibited around
catchments. Agriculture and industry can contribute heavy metals or nutrients from
fertilisers to water, catchments are distanced from these areas
At treatment plant:
o Screening – large debris such as rubbish which can interfere with treatment is removed
Clarification - These processes remove turbidity and colour to give water optical clarity
o Flocculation/Sedimentation – aluminium sulphate or ferric oxide added to cause
precipitation of fine suspended particles, otherwise kept apart by surface charge. The
particles build as smaller particles adsorb onto them, coagulating to form large lumps. In
this process, dissolved particles can also become physically trapped. Resulting mixture is
settled in sedimentation tank and sludge removed
Is able to removed dissolved and suspended particles
o Filtration – water is pushed through sand/anthracite filters which trap small particles
Cannot remove extremely small particles
Fast enough to produce adequate volume of water for big cities
i. Reducing dissolved organic carbon – improves taste and odour, allows water
to be safely chlorinated and makes it easier to further treat for domestic use
• Describe the design and composition of microscopic membrane filters and explain how
they purify contaminated water
o Thin film of synthetic polymer (e.g. polypropylene) or ceramic with microscopic holes of
approximately uniform size. Holes made by beam of ions through sheet of polymer, then
washing in alkaline solution. Changing ion changes pore size. Various forms include a
folded sheet which can be placed into pipes and used, or a bundle of hollow tubes – all of
which are very thin, so that water can flow through more quickly
Diagram:
o Reverse osmosis filters consist of cellulose
acetate or polyamid attached to another
polymer
o Water forced through the tiny holes by gravity,
vacuum or pressure pumps, which traps larger
particles and allows smaller particles through
o These trapped larger particles are water
contaminants such as bacteria and suspended
matter, whilst water molecules are small
enough to pass freely through
o This results in purer water
o The particles filtered depends on the size of the holes:
Microfiltration – inorganic and biological particles included supsnded solids,
protozoans and bacteria
Ultrafiltration – can remove fine suspended particles, viruses and water
borne parasites such as Giardia
Reverse osmosis – can filter out viruses, bacteria, antibiotics and other
chemicals
• Present information on the features of the local town water supply in terms of:
o Catchment area
Chem notes David Lee BHHS 2007 64
o Possible sources of contamination in catchment
o Chemical tests available to determine levels and types of contaminants
o Physical and chemical processes used to purify water
o Chemical additives in the water and the reasons for the presence of these additives
Chemical tests
o AAS for heavy metals
o Winkler method for DO/BOD
o pH testing using data logger
o Chloride ion titration
• Gather and process information from secondary sources to identify and analyse the
chemical composition of an identified range of pigments
• Analyse the relationship between the chemical composition of the metallic component(s)
of each pigment in the periodic table
• Explain that colour can be obtained through pigments spread on a surface layer (e.g.
paints) or mixed with the bulk of material (e.g. glass colours)
o Lakes are organic pigments sourced from plants and animals e.g. cochineal (crimson)
from insects, tyrolean purple from marine snail
o They are soluble, don’t get depth and intensity of inorganic pigments, and are broken
down by UV radiation and fade
Vehicle:
o Can consist of:
A binder which controls flow properties of coating and hardens on exposure
to air and gives bulk, gloss and toughness to paint film (natural oils, synthetic
organic compound, gum). Drying oils are polyunsaturated, polymerised due
to opening of C=C causing chain cross-linking. They physically lock in
pigments and are effective binders e.g. linseed/walnut oil
Thinner which is a solvent to facilitate application
Drier – a metal soap which speeds up drying of alkyl-based paint
o Affects drying time and thickness
o Needs to:
Wet particles of pigment
Sufficient viscosity to hold particles in suspension when drying
Capacity to form tough adherent film on surface
Pigments need to be insoluble since they are not easily removed or affected by rain or perspiration
(makes them moisture resistant). Pigment needs to be opaque and reflective so colour is vibrant (in
many cases)
Other:
Attachment of gold leaf – graffito, gold leaf painted over and then design scratched to reveal it –
gilding.
Mordant gilding – thin lines of adhesive painted on surface, gold leaf cut and adheres to adhesive,
any excess is brushed away
• Identify the sources of the pigments used in early history as readily available minerals
• Identify minerals that have been used as pigments and describe their chemical
composition with particular reference to pigments available and used in art by Aborigines
Early pigments derived directly from naturally occurring coloured earth and soft rocks e.g.
Ochres (natural earth of silica and clay), and kaolin were used extensively by the aboriginals:
The Egyptian, Roman and Greek cultures used pigments as cosmetics, mostly mixed with water or
saliva. Egyptians used kohl [made up variously of stibnite (Sb2S3), black manganese oxide (MnO2),
lead and CuO] as mascara after being wetted with saliva. Orpiment was used as yellow eye shadow.
All three cultures used white lead (PbCO3) for face paint. Greeks used vermillion (chemically same
as cinnabar): produced heating mercury and sulfur together in flask – taken out and ground. Henna
was also used in Egypt to dye fingernails, palms and soles, and hair.
• Identify the chemical composition of identified cosmetics used in an ancient culture and
use available evidence to assess the potential health risk associated with their use
In Egypt:
Pigment Composition Use Hazard
Cinnabar HgS Rouge, lipstick Mercury is not harmful in pure form, but
Vermillion harmful if allowed to combine with oxygen
and hydrogen in water and air. Toxic by
ingestion and inhalation in large doses.
Results in numbness, staggered walk, tunnel
vision and brain damage
Galena Contains (PbS) Eyeshadow Harmful in small amounts. Most is removed
in urine, but there is risk of buildup.
Damages nervous system, causes mental
retardation and death
Yellow As2S3 Eyeshadow Highly toxic, can cause: vomiting; diarrhea;
Orpiment nausea; numbness
Malachite CuCO3.Cu(OH)2 Eye paint Can cause anemia, liver and kidney damage,
and stomach/intestinal irritation in high
doses
• Describe an historical example to illustrate the relationship between the discovery of new
mineral deposits and the increasing range of pigments
These different pigments provided new shades of colours or new colours altogether.
• Describe the development of the Bohr model of the atom from the hydrogen spectra and
related energy levels to electron shells
• Explain why excited atoms only emit certain frequencies of radiation
• Explain what is meant by ‘n’, the principle quantum number
• Identify that, as electrons return to lower energy levels, they emit quanta of energy which
humans may detect as a specific colour
Bohr calculated a set of allowed energies using the hydrogen spectrum, and the principle quantum
number ‘n (a cardinal)’ denotes the energy level of a particular orbit. Energy is emitted or absorbed
by an atom when an electron moves from one stationary state to another. The difference in energy
between initial and final states is equal to the difference in energy between the initial and final
energy levels.
The lines in the hydrogen spectrum represent a drop from higher energy to lower energy (return to
ground state). Energy of photon is exactly equal to energy difference between levels. Some of this
radiation corresponds with radiation in visible spectrum.
• Solve problems and use available evidence to discuss the merits and limitations of the
Bohr model of the atom
Merits:
Chem notes David Lee BHHS 2007 69
o Explained the observation that excited atoms generated discrete spectra
o Predicted with reasonable accuracy the emission spectrum of hydrogen
o Incorporated the idea of ‘quanta’ into a model of the atom
Limitations:
o When applied to other atoms, predictions failed to agree with experimental results
o Could not explain closely spaced emission lines, or the further energy splitting by
magnetic fields
o Did not explain why certain radii were permitted, or why moving electrons did not lose
energy
o Did not explain the different intensities of these lines
• Gather and process information from secondary sources to analyse the emission spectra
of sodium and present information by drawing energy level diagrams to represent these
spectral lines
• Identify Na+, K+, Ca2+, Ba2+, Sr2+ and Cu2+ by their flame colour
• Perform first-hand investigations to observe the flame colours above
Na+ - yellow
K+ - violet
Ca2+ - orange-red
Ba2+ - apple green
Sr2+ - red
Cu2+ - blue-green
Risk analysis:
Hazard Risk Control
HCl Corrosive. Can cause Wear safety glasses, have
permanent eye damage sodium bicarbonate to
Kills tissue neutralise spills
Bunsen flame Wire heated in hottest part Protective gloves
of flame, can cause burns
• Explain the flame colour in terms of electrons releasing energy as they move to a lower
energy level
The flame is a source of energy that can be absorbed by electrons in the atoms to be excited and
move to higher energy states. When they return to ground state, they release energy in the form of
EM radiation, which corresponds with frequencies in visible spectrum, producing colour.
• Distinguish between the terms spectral line, emission spectrum, absorption spectrum and
reflectance spectrum
o Spectral line – a discrete wavelength of light emitted by a radiant source, light emitted
by an atom is quantised, not continuous
o Emission spectrum – a set of discrete spectral lines corresponding to the energies
emitted by an excited atom, represented by bright lines against dark background
o Absorption spectrum – the specific wavelengths of light absorbed by an atom,
appearing as dark lines across a continuous spectrum. Complementary to emission
spectrum
o Reflectance spectrum – the wavelengths of light reflected by an element
• Outline the use of infra-red and ultraviolet light in the analysis and identification of
pigments and their chemical composition
Quantitative methods:
o IR absorption spectroscopy
A double-beam spectrometer is used. One beam passes through the sample
and another through the reference
A mono-chromator is used to select particular frequencies of IR to pass
through the sample and reference
The molecules in a compound ‘vibrate’, and absorb radiation of same
frequency of their natural vibrational frequency, causing less radiation to be
transmitted
The pattern of absorption is unique for each compound due to mass of atom,
and length/strength of bonds
A detector compares the energy that is transmitted by the sample with that of
the reference – an absorption spectrum is plotted from the difference
This absorption spectrum can be compared with standard absorption spectra
for certain functional groups and compounds, allowing identification of
pigments used
• Explain the relationship between the absorption and reflectance spectra and the effect of
infra-red and ultraviolet light on pigments including zinc oxide and those containing
copper
o The reflectance and absorption spectra are complements of each other when sample is
opaque
o Represented as plots of wavelength against intensity of reflection/absorbance
o A material can either reflect or absorb a particular wavelength
o Thus, the non-reflected wavelengths must be absorbed and vice versa
o Putting the two spectra together gives you the original radiation spectrum
IR:
o Far IR radiation can change the colour of zinc oxide from white to yellow in the presence
of oxygen due to increased temperature, this is reversible by decreasing temp
o Red copper (I) oxide and malachite permanently change to black copper (II) oxide since
the heat causes breakdown
UV:
o ZnO (zinc white) fluoresces a pale yellow, while green malachite is a dirty mauve
(CuCO3.Cu(OH)2), since they absorb the radiation but the electrons don’t return
immediately to ground state, going down transitional stages and thus emitted different
wavelengths to the originally absorbed one
• Gather, process and present information about a current analytical technology to:
o Describe the methodology involved
o Assess the importance of the technology in assisting identification of elements in
samples and in compounds, and
o Provide examples of the technology’s use
Importance:
o Laser beam is very intense, pure and focused, allowing the technique to detect trace
amounts of elements in samples
o It is useful for determining authenticity, and in restoration
o Requires minimal preparation, so can be used for a variety of solid samples
Examples of use:
o Analysis of paintings for validity (time period etc.)
o Used to analyse chemical compositions of paintings so correct restorative chemicals are
used
• Define the Pauli Exclusion Principle to identify the position of electrons around an atom
No two electrons in an atom may have identical sets of four quantum numbers
Only two electrons which have opposite spins (anticlockwise, clockwise). These produce magnetic
fields, and result in slightly different energy levels for each electron. Note: This arrangement
produces a lower potential energy than if they were paired, since the electron-electron repulsion is
minimised
A sub-shell is an energy sublevel within a principle energy level (or shell). S, P, D, F. Number of
subshells = principle energy level. S – spherically symmetrical around nucleus, P – dumbbell
shaped with 3 orientated in perpendicular planes through nucleus
• Identify that electrons in their ground-state electron configurations occupy the lowest
energy shells, sub-shells and orbitals available to them and explain why they are able to
jump to higher energy levels when excited
When an electron absorbs a quanta of energy corresponding to the difference between its current
energy level and another energy level, it moves to the higher energy level to expend this energy.
Chem notes David Lee BHHS 2007 74
• Explain the relationship between the elements with outermost electrons assigned to s, p, d,
f blocks and the organisation of the periodic table
o Elements with similar outer shell electron configurations occur in the same group
o Periods correspond to principle energy levels
o The periodic table is divided into blocks depending on the element’s outer shell
• Explain the relationship between the number of electrons in the outer shell of an element
and its electronegativity
Electronegativity – a measure of the ability for an atom to attract electrons to itself in a chemical
bond
Electronegativity increases across a period – more protons in nucleus meaning increased nuclear
charge. Electrons added do not fully shield each other from effect of increased protons, meaning
electrostatic force on electrons around the nucleus is stronger
Electronegativity decreases down a group – the size of an atom increases, and the attractive force
of the nucleus on valence electrons is diminished
• Analyse information about the relationship between ionisation energies and the orbitals
of electrons
• Describe how trends in successive ionisation energies can be used to predict the number
of electrons in the outermost shell and the sub-shells occupied by those electrons
In the p,d,f-subshells, the ionisation energy increase as the electrons are added into different orbitals
(See above), but decreases when an electron is first paired in an orbital. This is because the
electrons repulse each other enough to overcome the effect of increased nuclear charge, raising each
other to higher potential energies and decreasing ionisation energy.
It decreases down a group as valence electrons are further from the nucleus, and thus at higher
potential energies.
• Use Hund’s rule to predict the electron configuration of an element according to its
position on the periodic table
Hund’s rule – every orbital in a subshell must be singly occupied by one electron with identical
spin before any one of these orbitals in the same subshell are doubly occupied
Transition element - those that form at least one ion with a partially filled sub-shell of d electrons
Zn is not a transition element since its ion Zn2+ has a completely filled d-subshell. Scandium ion
(Sc3+) has no electrons in d-subshell.
• Explain why transition metals may have more than one oxidation state
• Account for colour changes in transition metal ions in terms of changing oxidation states
• Explain, using the complex ions of a transition metal as an example, why species
containing transition metals in a high oxidation state will be strong oxidising agents
Oxidation number is the charge an atom would have in a chemical bond if the bonded electrons
belonged to the more electronegative element.
The number of oxidation states for the first period of transition elements progressively increases to
a peak at VIIB then decreases, since:
o As more electrons are added to a d-orbital, the d and s subshells progressively separate in
terms of energy due to electron repulsion
o However, more electrons also means more possible oxidation states
o The “sweet spot” is Mn, with the number decreasing to the left due to lack of electrons,
and decreasing to the right due to separation of energy levels
CHECK – why do transition metals need to be in oxidised states for this to occur?
CHECK – what about return to ground state, wouldn’t it release the light again?
Transition metals ions in compounds have d orbitals with slightly different energy levels and are
incompletely filled. These energy differences correspond with the energy of visible light, and
electrons in the d subshell can absorb photons to become excited, meaning the complementary light
spectrum is able to pass through and be observed. E.g. transition metals which absorb the red end of
the spectrum will appear blue.
Chem notes David Lee BHHS 2007 76
In different oxidation states, the transition metal has a different arrangement of filled and unfilled
3d orbitals, causing differences between d energy levels and thus causing different wavelengths of
visible light being absorbed.
Transition metals in a high oxidation state have a high deficit of electrons, which reduces the orbital
radii and decreases electron shielding. This results in a high oxidation potential and makes them
strong oxidising agents. E.g. Cr2O72- and MnO4-
As per Hund’s Rule. Note: The d-orbitals are in their most ‘stable’ configuration with a complete
set of unpaired or paired electrons. When the set is almost complete, an electron from the 4s orbital
will transit to make it complete (Chromium and Copper).
Method:
1. 3 grams of ammonium vanadate was weighed on an electronic beam balance
2. 100 mL of 1M NaOH and the 3 grams ammonium vanadate were added to the conical flask
3. The mixture was swirled to dissolve
4. 75 mLs of 2M H2SO4 was added to the solution to acidify it
5. 20 mL of the resulting solution was poured into a test tube using a 50 mL measuring cylinder
6. 8 granules of zinc were dropped into the conical flask which was then stoppered
7. The solution was swirled gently until it became blue, then step 5 performed
8. The solution was swirled again until it became green, then step 5 performed
9. The flask was swirled vigorously until the solution became violet, then step 5 performed
Risk analysis:
Hazard Risk Control
Sulfuric acid Corrosive. Can cause Wear safety glasses, use
permanent eye damage lower concentrations
Kills tissue
Sodium Hydroxide Corrosive. Can cause Wear safety glasses, use
permanent eye damage lower concentrations
Kills tissue
Ammonium vanadate Eye contact causes redness Safety goggles, gloves, do
and swelling not make airborne
Skin contact causes itching
and pain
In alkaline solution:
1. Balance as though in acid solution
2. H+ ions are removed to form H2O by adding same number of OH- ions to both sides
3. Simplify
e.g.
[MnO4-(aq) + 4H+(aq) + 3e- MnO2(s) + 2H2O(l)]
[MnO4-(aq) + 4H+(aq) + 4OH-(aq) + 3e- MnO2(s) + 2H2O(l) + 4OH-]
[MnO4-(aq) + 2H2O(l) + 3e- MnO2(s) + 4OH-]
Mg2+ < Zn2+ < Sn2+ < Cu2+ < I2 < Fe2+ < Br2 < Cl2 < MnO4-
Risk analysis:
Hazard Risk Control
Potassium permanganate Stains skin and clothing, Wear safety glasses, use
concentrated solutions are lower concentrations
corrosive
Toluene Very flammable Keep away from hot
Skin irritant surfaces, flames or sparks
Polyvinyl gloves
Sulfuric acid Corrosive. Can cause Wear safety glasses, use
permanent eye damage lower concentrations
Kills tissue
The permanganate ion is a strong oxidant due to the presence of manganese in a high (+4) oxidation
state. This gives it a high electronegativity, thus making it a strong oxidant and in turn a weak
reductant.
When an ionic solid dissolve in water, the ions dissociate and are surrounded by water molecules in
a process called hydration. The charge of the ion attracts the polar water molecule. These ions are
The general formula is [M(OH2)n]m+ where ‘m’ is the charge of the ion and ‘n’ is the no. of water
molecules surrounding the ion. Note that it is OH2 since the “O” is donating the electrons.
Note that many other ligands are possible.
A complex ion (a lewis acid) is where a central metal ion is surrounded by ligands. Ligands (a
lewis base) are atoms, ions or molecules which donate one or more electrons in a coordinate
covalent bond with the central metal ion. Ligands therefore need a lone pair of electrons which it
can donate to an empty orbital of the central ion, in order to bond.
Ligands can bond using different numbers of electron pairs. Monodentate ligands bond using the
electron pair of a single donor atom. Others have multiple atoms with unpaired electrons and can
bind simultaneously, and are polydentate or chelated ligands. Note: Memorise ‘en’ and ‘EDTA’
Models are significant in understanding the nature of ligands. They allow us to specify mechanisms
for the formation and bonding of ligands, and other phenomena where the mechanism cannot be
directly observed but only inferred (e.g. colours). They are not necessarily true, but are adequate
explanations for current use.
1. The electron pairs from the ligands are placed in empty orbitals of the central ion
2. These orbitals are hybridized, that is, they are mixed to form new orbitals
3. Some ligands cause unpaired electrons in d-orbitals to pair with other unpaired electrons, and
then use the newly empty d-orbitals. Others cannot do this, and use completely vacant orbitals.
4. Those ligands utilising d-orbitals previously occupied have inner spin complexes, the ones not
have outer spin complexes
5. Inner spin complex are paramagnetic, and move in the direction of a magnetic field. Outer spins
are diamagnetic, and move opposite to the direction of a magnetic field
6. The structural geometry can be determined using VSEPR rules
Disadvantages:
o Cannot show details such as the energy changes involved, rate at which reactions occur
and the mobility/flexibility of bonds involved
o Cannot account for colours of transition metal compounds
The ligand is treated as a point negative charge, and when it approaches the central metal ion, the
electron clouds of both get disturbed, resulting in changed energy states for orbitals such as the d-
orbitals. Different ligands and different metal complex geometries result in different degrees of
energy separation. The resulting separation of the d-orbitals is in the energy range of visible light,
and different energies absorb different wavelengths, resulting in different observed colours.
Advantages:
o Explains the colours of transition metal complexes
Disadvantages:
o Neglects any covalent contribution
Chem notes David Lee BHHS 2007 81
• use available evidence and process information from secondary sources to draw or model
Lewis structures and analyse this information to indicate the bonding in selected complex
ions involving the first transition series
Some examples:
• process information from secondary sources to give an example of the range of colors
that can be obtained from one metal such as Cr in different ion complexes
The colour depends on the central metal ion (element and oxidation state) and the surrounding
ligands.
0. [Cr(H2O)6]3+ (blue)
1. [Cr(H2O)5SO4]+ (green)
2. [Cr(H2O)4Cl2]+ (green)
3. Cr(H2O)3(OH)3 (grey-blue ppt)
4. [Cr(OH)6]3- (green)
5. [Cr(NH3)6]3+ (mauve)
Errata:
1). Added an actual evaluation in the summary of ethanol usage, changed it
2). The diagram for dry cell is incorrect (page 23-24)
3). Some content changes made to reflux (page 45)
4). Defined allotrope (page 54)
5). Added risk analysis (page 69)
6). Big error!! Explanation of why transition metals compounds are coloured was
incorrect before. See last sentence of paragraph below table (page 64)
7). Should be bromine water not iodine in the lycopene prac (page 7)
8). Ester structure clarified. The way I wrote them as word equations before was
misleading (page 44)
9). Completed the IR Absorption spectroscopy description (page 71)
10). Made risk analysis more specific for bromine water prac (page 6)
11). Scintillation counter description before was INCORRECT (page 27)
Chem notes David Lee BHHS 2007 82
12). Modified the explanation explaining multiple oxidation states of transition
metals
13). Ester page updated with more information (page 44)
14). Made the uses of ethylene page more readable
15). Error! Iron sulfide in coal (production of sulfur dioxide) – equation is incorrect,
see correction page (34)
16). Expanded description of Arrhenius acids, including limitations, and also
Bronsted-Lowry theory (page 39)
17). Clarified conjugate base/acid explanation (page 39)
18). Changes to history of pigment use – I got kohl composition wrong
19). Amphoteric is NOT amphiprotic! Amphoteric means it has both acidic and basic
PROPERTIES. Amphiprotic means it can both accept and donate protons which ARE
properties of most acids/bases but do not encompass all of them