MINISTRY OF EDUCATION

LUANGWA SECONDARY SCHOOL

DEPARTMENT OF NATURAL SCIENCE

CHEMISTRY ASSIGNMENT FOR GRADE 12B, C &D ONLY.

NOTE:
BOTH THE ASSIGNMENT AND NOTES TO BE SUBMITTED ON THE 25TH MARCH,
2024

SECTION A

Answer this section in the grid below

1 2 3 4 5 6 7 8 9 10 11 12 13 14

1. The nuclide of aluminum ion is written as 2713Al 3+

, state the numbers of
neutrons and electrons in the nuclide of the ion.
Neutrons Electron
A. 27 13
B. 14 13
C. 14 10
D. 27 10.

2. The chemical formula of ammonium sulphate is …

A. NH4SO4 B. (NH4)2SO3 C. (NH4)2SO4 D. NH4SO3

3. The atoms 3115P and 3216S have the same …

A. Nucleon number. B. number of electrons.
C. Number of neutrons D. Number of protons

4. What is the formula mass of magnesium nitrate, Mg (NO3)2?

A. 54 B. 74 C. 148 D. 296

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 5. How many moles of oxygen molecules are there in 64 grams of oxygen,
O2?
A. 2 moles B. 4 moles C. 8 moles D.16
6. Dilute hydrochloric add reacts with both magnesium oxide and calcium
carbonate.
What is common about these reactions?
A. Carbon dioxide is produced
B. Water is produced
C. Water vapour is condensed
D. A white precipitate is formed

7. How many atoms are there in 6.0g of carbon atoms?

A. 2 x 1023 B. 6 x 1023 C. 1.2 x 1024 D. 6 x 1024

8. The graph below shows the rate of reaction between a metal and a dilute
acid.

Which reaction on the graph was the fastest?

A. 1 only B. 4 only C. 1 and 4 D. 2 and 3

9. Which of the following explains the importance of catalysts in chemical

reactions? They…
A. Enable the activation energy to be lowered.
B. Enable reactants to be consumed completely.
C. Help to conserve reactants and products.
D. Offer more energy for the reaction to take place

10. Which of the following alkanes has the highest boiling point?

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 A. CH4 B. C2H6 C. C3H8 D. C4H10
SECTION: B
B1. (a) Define a hydrocarbon.
………………………………………………………………………………………
…………………………………………………………………………………… [1]
(b) State the difference between saturated hydrocarbons and unsaturated
hydrocarbon.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
…………………………………………………………………………………. [2]
(c) Organic compounds form homologous series.
Give two characteristics of members of any homologous series.
……………………………………................................................................
……………………………………………………………………………… [2]
(d) (i) Draw the structure of an alkane with two carbon atoms in the molecule.

[2]
(ii) Calculate the percentage by mass of hydrogen in this alkane.
……………………………………………………………...........................
…………………………………………………………………………… [2]
[Total: 9 marks]

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 B2. The diagrams below show the electron arrangement in the outer shell of five
elements A to E.
All elements are from Period 3 of the Periodic Table.

(a) Put the letters A to E in the table to shows which elements are metals and
which are non-metals.
Metals Non-metals

[5]

(a) Which element is most likely to be in Group VI of the Periodic Table?

…………………………………………………………………………… [1]

(b) Which element will form an ion of the type X2+?

……………………………………………………………………………. [1]
(c) Which element has an atomic number of 15?
…………………………………………………………………………... [1]
[Total: 5marks]

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SECTION: C
Answer all questions from this section

C1. The table below shows the results of the production of hydrogen in the reaction
between zinc granules and dilute hydrochloric acid at 25oC.

Volume (cm3) 0 5.0 10.0 13.0 15.5 18.5 19.5 19.5 19.5
Time (Min) 0 0.6 1.5 2.3 3.0 4.4 5.7 7.0 7.5

(a) Plot a graph of volume against time for the reaction [3]
(b) Calculate the average rate of the reaction during the first 3
minutes [2]
(c) Use the graph to determine the volume of gas collected after 5 minutes
[2]
(d) On the same graph, sketch a curve you would expect if powdered
zinc were used instead of zinc granules. Label this curve P [1]
(e)How long did it take for the reaction to end? [1]
(f) Mention factors you would employ to increase the rate of production of
the gas. [3]
(g), Explain briefly how each of the mentioned factors above increases the
rate of production of the gas.
[6]

[Total: 18 marks]

C2. (a) Work out the relative formula mass, Mr of the following:
(i) Ca(HCO3)2 (ii) Al2(SO4)3 [2]

(b) When water containing dissolved calcium hydrogen carbonate is boiled, the
calcium hydrogen carbonate decomposes according to the equation below:
Ca(HCO3)2(aq) CaCO3(s) + H2O (l) + CO2(g)

(i) Name the white solid formed in this reaction. [1]

(ii) If the water boiled contained 16.2g of Calcium hydrogen carbonate, calculate
the mass of CaCO3 formed. [2]

[Total: 5 marks]

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C3. A piece of Magnesium ribbon was made to react with dilute hydrochloric acid. The
volume of the hydrogen gas collected in a syringe was measured at intervals. The results
are shown below.
Gas syringe

RESULTS
Time/minutes 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Volume of hydrogen gas 0 8 14 20 25 35 33 36 38 39 40 40 40
3
(cm )
(a) Write a balanced chemical equation for the reaction between magnesium and
dilute hydrochloric acid (include state symbols). [3]
(b) Plot a graph of the results (volume against time) on the graph paper provided. [3]
(c) Which result should be rejected as being an error? [1]
(d) What was the maximum volume of hydrogen produced in this reaction? [1]
(e) From the graph, how can you tell when the reaction came to an end? [1]
(d) What is the average rate of this reaction? [1]
[Total: 10 marks]

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NOTES

Organic chemistry
Definition: Organic chemistry is the study of carbon compounds except carbonates,
carbon monoxide, carbon dioxide, carbon disulphide etc.
Common terms used
1. Organic compounds
Organic compounds are compounds which contain carbon except carbonates, carbon
monoxide, carbon dioxide, carbon disulphide etc.
2. Hydrocarbon
A hydrocarbon is a compound which consists of the elements carbon and hydrogen only,
Example
Hydrocarbon Formula
Methane
Ethene
Ethyne

3. Homologous series
A homologous series is a family of similar organic compounds
Each member in a family is called homologue
Characteristics of the homologous series
(a) Members in the family show a gradual change in physical properties i.e.
change from gas to liquid and solid as the carbon chain increases.
(b) Members in the family have similar methods of preparation
(c) Members in the family have similar chemical properties because they have
the same functional group.
(d) Members in the family can be represented by the general molecular formula:
Example
Organic family General molecular formula
Alkanes

Alkenes

Alkynes

Alcohols (Alkanols)

Carboxylic acids (Alkanoics)

Esters

(e)Each member in the family differs to the next by or by 14.

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4. Functional group
A functional group is a group is a group which determines the chemical properties of
organic compounds
Organic family Functional group Name of functional group
Alkanes ─C─C─ Single carbon – carbon covalent bond
Alkenes C=C Double carbon – carbon covalent bond
Alkynes C≡C Triple carbon – carbon covalent bond
Alkanols ( alcohols) ─ OH Hydroxyl group
─ COOH
or
Alkanoics (carboxylic Carboxyl group
acids)

Esters − COO − Ester functional group

Nomenclature of organic compounds

Nomenclature is a standardized way of naming organic compounds.
Nomenclature takes into account the following:
• Prefix
• Suffix

The prefix shows the number of carbon atoms in an organic compound.

Prefix Number of carbon atoms
Meth 1
Eth 2
Prop 3
But 4
Pent 5
Hex 6
Hept 7
Oct 8
Non 9
Dec 10

The suffix shows the organic family of the organic compound.

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 Suffix Organic family
ane Alkanes
ene Alkenes
yne Alkynes
anol Alcohols
anoic Carboxylic acids
anoate Esters

Alkanes
Alternative term: Saturated hydrocarbons
General molecular formula: where n = 1, 2, 3, 4…….
Alkanes have single carbon – carbon covalent bonds between carbon atoms.
They are called saturated hydrocarbons because they have the required (maximum)
number of hydrogen atoms. They end with ane

Examples of alkanes

Alkane Molecular Structural formula Condensed Mr

formula formula

Methane CH4 CH4 16

Ethane C2H6 CH3CH3 30

Propane C3H8 CH3 CH2CH3 44

Butane C4H10 CH3 (CH2)2CH3 58

Pentane C5H12 CH3 (CH2)3CH3 72

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Preparation of methane
Methane can be prepared by heating a mixture of anhydrous sodium ethanoate,
COONa, and soda lime (sodium hydroxide), NaOH.
Reaction: COONa(s) + NaOH(s) → CH4(g) + Na2CO3(s)
Diagram:

Physical properties of alkanes

1. Their physical states vary at room temperature and pressure. Lower members
are gases; others are liquids while higher members are solids.
2. Their melting and boiling points increases as the carbon chain (relative
molecular masses) increases.
3. Their densities increase as the carbon chain increases.
Chemical properties of alkanes
1. Combustion
(a) In a plentiful supply of air (complete combustion), alkanes react with
oxygen to form carbon dioxide and water. Example
CH4+ 2O2 → CO2 + 2H2O
(b) In a limited supply of air (incomplete combustion), alkanes react with
oxygen to form carbon monoxide and water
Example

2C2H6 + 5O2 → 4CO + 6H2O

(c) In a very limited supply of air (incomplete combustion), alkanes react with oxygen to
form carbon and water
Example
C3H8 + 2O2 → 3C + 4H2O

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 2. Substitution reaction
A substitution reaction is a reaction in which one atom or group of atoms in a molecule
is replaced by another.
Alkanes undergo substitution reactions with halogens in the presence of ultraviolet light.
Example
Halogenation of methane
Methane can react with chlorine gas in the presence of sunlight to form chloromethane
and hydrogen chloride.
CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)

Conditions

1. Temperature: 200oC
2. Catalyst: Sunlight (ultraviolet light)

Isomerism of alkanes

Isomerism is the existence of compounds with the same same molecular formula
but different structural formula Isomers

Isomers are compounds which have the same molecula formula but different structural
formula.

Alkanes with more than three carbon atoms exhibit isomerism

Nomenclature of alkane isomers

The International Union for Pure and Applied Chemistry (IUPAC) rules for naming
alkanes

• Choose the longest continuous carbon chain in the molecule.

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 • Number the carbon atoms in the longest chain chosen starting from the end that
gives the smaller set of numbers nearer the branched methyl group
• Write the number of carbon atom at which the branched methyl group is
attached to the main chain in alphabetical order.
• Put a comma after each group number and a hyphen between the group number
and the methyl group.
• Name the compound as a derivative of the normal alkane having the same
number of carbon atoms as in the longest chain chosen.

Example 1: Butane has two isomers

Molecular formula:
IUPAC name: Normal butane

Molecular formula:
IUPAC name: 2 – methyl propane

Example 2: Pentane has three isomers

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Molecular formula:
IUPAC name: Normal pentane

Molecular formula:
IUPAC name: 2 – methyl butane

Molecular formula:
IUPAC name: 2, 2 – dimethyl propane

Exercise

1. Draw the structure of the compound with the IUPAC name; 2, 3, 4, 4 – tetra
methylpentane

Cracking of alkanes

Cracking is the breaking down of large hydrocarbon molecules into simpler and smaller
molecules.

Alkanes break down to produce alkenes, short chain alkanes and in some cases hydrogen
gas.

Types of cracking
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 1. Thermal cracking
This is where heat is used to break down large molecules into smaller ones.

Example

C4H10 → C2H6 + C2H4

C2H6 → C2H4 + H2

2. Catalytic cracking
This is where both heat and a catalyst are usedto break down large molecules into
smaller ones.
Common catalysts used include aluminium oxide (Al2O3) and silica (SiO2).

Example

C17H36(l) → 3C2H4(g) + C8H18 + C3H6(g)

Conditions

1. Catalyst: Aluminium oxide, Al2O3

2. Temperature: 600oC

Importance of cracking

1. It is used in the production of raw materials for petrol chemicals like ethene and
hydrogen.
Hydrogen is used in making plasitics and margarine.
2. It is used in the production of petrol.

Exercise

1. One of the hydrocarbons found in crude oil is undecane,

Under suitable conditions, undecane under goes the reaction below
→ +
(a) What term is used to describe this type of reaction in the petrochemical
industry? (b) State two conditions necessary for this reaction to take place

Fuels

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A fuel is a substance which burns in air to produce useful energy.

Sources of fuels

(a) Natural gas

The main component of natural gas is methane.
Natural gas is usually mined and purified before use.

(b) Crude oil

Alternative term: Petroleum
Crude oil is a mixture of long chain hydrocarbons and some elements like sulphur and
nitrogen
Crude oil was formed millions of years ago by the decomposition of animals and plants
under pressure.
Crude oil can be refined by fractional distillation.
Fractional distillation is a process of separating components of a mixture based on their
boiling points.
The diagram below shows a fractionating tower and different fractions obtained from
crude oil.

Fractions of crude oil and their uses

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 Fraction Number of carbon atoms Use
Petroleum gases C1 – C4 Used in camping stoves and cookers as
bottled gas
Petrol (gasoline) C4 – C10 Used as a fuel in internal combustion
engines in vehicles
Kerosine ( paraffin) C10 – C17 Used as a fuel in jets
Used in paraffin lamps for lighting
Used in paraffin lamps for cooking
Diesel oil (gas oil) C17 – C20 Used as a fuel in diesel engines like trains,
hammer mills, tractors, lorries
Lubricating oil C20 – C30 Used as a lubricant in machines to reduce
friction
Fuel oil C30 – C40 Used as a fuel in ships, power stations and
industrial machinary
Paraffin waxes C40 – C50 Used in making waxes, polishes and wax
papers
Bitumen (residue) C50 upwards Used to tar roads
Used as a roofing material

Note

1. Petroleum gases have the smallest boiling point and have the smallest relative
molecular mass.
2. Bitumen has the highest boiling point and have the largest relative molecular
mass. In addition, bitumen has the longest chain.
3. Octane is the main component of petrol

Exercise

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1. Crude oil, a mixture of hydrocarbons, can be separated by fractional distillation. The
diagram below shows a fractionating tower and different fractions obtained from crude
oil

(a) What is meant by the term hydrocarbon?

(b) Which fraction contains the longest chain?
(c) State one major use of fraction:
(I) C
(II) D
(III) E
(d) State the process involved when ethene is manufactured from one of the
fractions obtained by the fractional distillation of crude oil.

Production of hydrogen from methane

Methane reacts with steam to form carbon monoxide and hydrogen gas.

CH4(g) + H2O(g) → CO(g) + 2H2(g)

Conditions

1. Temperature: 200oC
2. Catalyst: Nickel metal

Exercise

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1. Hydrogen can be manufactured from methane using a nickel catalyst as shown in the
diagram below

(a) Identify the substances X and Y

(b) Write a balanced chemical equation for the reaction in the manufacure of
hydrogen
(c) State one chemical property of hydrogen
(d) State one industrial use of hydrogen

Alkenes

Alternative term: Unsaturated hydrocarbons

General molecular formula: where n = 2, 3, 4, 5…..

Functional group: Double carbon – carbon covalent bond,

C= C

They have one or more double bonds between carbon atoms.

They end with ene.

They are called unsaturated hydrocarbons because they have a double bond between
carbon atoms.

They have two hydrogen atoms less than their corresponding alkanes

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Examples of alkenes
Alkene Molecular formula Structural formula Condensed formula Mr

Ethene C2H4 CH2=CH2 28

Propene C3H6 CH2=CHCH3 42

Butane C4H8 CH2 =CHCH2CH3 56

Pentene C5H10 CH2 =CH(CH2)2CH3 70

Preparation of ethene gas

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There are two methods used to prepare ethene.

1. Catalytic cracking of alkanes

This is where a catalyst is used to break down large hydrocarbon molecules into smaller
ones.

Reaction: C17H36(l) → 3C3H4(g) + C3H6(g) + C8H18(l)

Conditions

1. Temperature: 600oC
2. Catalyst: Aluminium oxide, Al2O3
Note: The broken pot can act as a catalyst.

2. Dehydration of ethanol

Ethene can be prepared by the dehydration of ethanol using concentrated sulphuric acid
as a dehydrating agent.

Sulphuric acid removes water.

C2H5OH(s) → C2H4(g) + H2O(l)

Conditions

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 1. Temperature: 180oC
2. Dehydrating agent: Concentrated sulphuric acid.

Test for unsaturation

Alternative term: Test for alkenes

There are two ways you could test a hydrocarbon, to see whether it is an alkane or

alkene Test 1: Shake an alkene with bromine water.

Result: The brown colour of bromine disappears immediately. In other words, alkenes
decolorize bromine water.

Explanation: When ethene reacts with bromine water, the colourless compound (liquid)
called 1, 2 – dibromoethane is formed.

C2H4(g) + Br2(l) → C2H4Br2 (l)

Note

When an alkane is shaken with bromine water, there is no reaction. Alkanes do not
undergo addition reactions because they are saturated.

Test 2: Add acidified potassium per manganate (VII) solution to the hydrocarbon.

Result: The purple colour of potassium per manganate (VII) turns colourless if an alkene
is present.

Chemical properties of alkenes e.g. ethene

Alkenes are more reactive than alkanes because the double bond opens up to allow
chemical reactions.

Alkenes undergo two notable chemical reactions.

1. Combustion

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Alkenes react with oxygen to form carbon dioxide and water.

Example

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)

2. Addition reactions

An addition reaction is a reaction where a molecule is added to an unsaturated molecule

by breaking a double bond.

Examples of addition reaction involving ethene

(a) Halogenation – reaction with halogens

Ethene reacts with chlorine to form 1, 2 – dichloroethane.

C2H4(g) + Cl2(g) → C2H4Cl2 (l)

(b) Hydrogenation – reaction with hydrogen

Alkenes react with hydrogen to form corresponding alkanes. Hydrogen makes the
unsaturated compounds to become saturated. Ethene reacts with hydrogen to form ethane

C2H4(g) + H2(g) → C2H6 (g)

Conditions

1. Temperature: C
2. Catalyst: Nickel metal

The reaction is important in the industry because it is used in the production of

margarine from unsaturated vegetable oil. Vegetable oils are changed into fats which are
saturated by hydrogenation.

(c) Hydration – reaction with water

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Ethene reacts with steam to in the presence of phosphoric acid to form ethanol.

C2H4(g) + H2O (g) → C2H5OH(l)

Conditions

1. Temperature: C
2. Catalyst: Phosphoric acid,
3. Pressure: 65 atmospheres
Uses of ethene

1. Used in the manufacture of plastics

2. Used in the manufacture of ethanol
3. Used in the process of ripening fruits

Exercise

1. Ethene, , is an unsaturated compound. It reacts with liquid bromine to form 1, 2 –

dibromoethane.
Ethane, is a saturated compound. It does not readily react with bromine
(a) Draw the full structural formula for ethene and 1, 2 – dibromoethane
(b) Write the equation for the reaction between ethene and bromine and name
the type of reaction taking place
(c) Ethene like many other unsaturated compounds can be polymerized.
Polyethene is formed when ethene is polymerized.

Name the compound which has the above stucture

(d) Margarine is manufactured using the addition reaction between hydrogen

and a vegetable oil
(I) State the conditions used for this reaction
(II) What type of bond must be present in the vegetable oil for this
reaction to take place?

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