GR 9 Chapter 2 (2.1,2.2) The Nature of Matter
GR 9 Chapter 2 (2.1,2.2) The Nature of Matter
GR 9 Chapter 2 (2.1,2.2) The Nature of Matter
Chapter 2 (2.1,2.2)
IGCSE Grade 9
Syllabus
It says
● that everything is made of particles
● that all particles constantly move.
Mixture
A mixture is made when two or more substances are combined, but they are not combined chemically.
Types of Mixtures
● There are two main categories of mixtures: homogeneous mixtures and heterogeneous mixtures. In a homogenous
mixture all the substances are evenly distributed throughout the mixture (salt water, air, blood). In a heterogeneous
mixture the substances are not evenly distributed (chocolate chip cookies, pizza, rocks)
Within the categories of homogeneous and heterogeneous mixtures there are more specific types of mixtures including
solutions, alloys, suspensions, and colloids.
Viscosity of fluids.
Viscosity of often referred to as the thickness of a fluid. You can think of water (low viscosity) and
honey (high viscosity). However, this definition can be confusing when we are looking at fluids with
different densities.
At a molecular level, viscosity is a result the interaction between the different molecules in a fluid.This
can be also understood as friction between the molecules in the fluid. Just like in the case of friction
between moving solids, viscosity will determine the energy required to make a fluid flow.
What is Volatility?
A substance is said to be volatile if it boils at a low temperature, changing from the
liquid to the gas phase.
Substances that are gases at room temperature are extremely volatile: they have
high volatility. They can only be seen as liquids when exposed to low temperatures
or high pressures.
Gasoline, acetone (often found in nail polish remover), butyl acetate (the source
of the fruity smell in a lot of coatings formulations), and alcohol (ethanol and
isopropyl) are all everyday examples of volatile fluids. A fluid is volatile when it has
a high vapor pressure.
Solutions (homogeneous)
A solution is a mixture where one of the substances dissolves in the other. The substance
that dissolves is called the solute. The substance that does not dissolve is called the
solvent.
In chemistry a solution is actually a type of mixture. A solution is a mixture that is the same
or uniform throughout. Think of the example of salt water. This is also called a
"homogenous mixture." A mixture that is not a solution is not uniform throughout. Think of
the example of sand in water. This is also called a "heterogeneous mixture."
Alloys (homogeneous)
An alloy is a mixture of elements that has the characteristic of a metal. At least one of
the elements mixed is a metal. One example of an alloy is steel which is made from a
mixture of iron and carbon.
Suspensions (heterogeneous)
A suspension is a mixture between a liquid and particles of a solid. In this case the
particles do not dissolve. The particles and the liquid are mixed up so that the
particles are dispersed throughout the liquid. They are "suspended" in the liquid. A
key characteristic of a suspension is that the solid particles will settle and separate
over time if left alone.
An example of a suspension is a mixture of water and sand. When mixed up, the
sand will disperse throughout the water. If left alone, the sand will settle to the
bottom.
Colloids (heterogeneous)
A colloid is a mixture where very small particles of one substance are evenly
distributed throughout another substance. They appear very similar to solutions, but
the particles are suspended in the solution rather than fully dissolved. The difference
between a colloid and a suspension is that the particles will not settle to the bottom
over a period of time, they will stay suspended or float.
Colloids are generally considered heterogeneous mixtures, but have some qualities
of homogeneous mixtures as well.
Interesting Facts about Mixtures
● Smoke is a mixture of particles that are suspended in the air.
● Tap water is a mixture of water and other particles. Pure water or
H2O is generally referred to as distilled water.
● Many of the substances we come into contact with every day are
mixtures including the air we breathe which is a mixture of gases like
oxygen and nitrogen.
● Blood is a mixture that can be separated by a machine called a
centrifuge into its two main parts: plasma and red blood cells.
● Mixtures can be liquids, gases, and solids.
Separating mixtures
The substances in a mixture are relatively easy to separate, because they are not chemically
joined to each other.
The components of a mixture can be separated without chemical reactions
T
The following terms are useful to know when thinking about separating mixtures.
You’ll have to choose the best separation technique when you’re asked to separate the components
of a mixture. This table can help:
Filtration
Distillation
Paper chromatography
The choice of the method of separation depends on the nature of the substances being separated.
All methods rely on there being a difference of some sort, usually in a physical property such as b.p.,
between the substances being separated.
Mixtures of solids
For example salt and sand,sugar and salt,carbon and sulphur,iron and sand,iodine and salt.
Mixtures of liquids
● Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and
water). Centrifugation can also be used for this mixture
● Filter paper is placed in a filter funnel above another beaker
● Mixture of insoluble solid and liquid is poured into the filter funnel
● Filter paper will only allow small liquid particles to pass through as the filtrate
● Solid particles are too large to pass through the filter paper so will stay behind as a residue
Crystallisation
● Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper
sulphate from a solution of copper (II) sulphate in water)
● The solution is heated, allowing the solvent to evaporate to leave a saturated solution behind
● Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form
on the glass rod
● The saturated solution is allowed to cool slowly and solids will come out of the solution as the solubility decreases, and crystals
will grow
● Crystals are collected by filtering the solution
● They are then washed with cold, distilled water to remove impurities and allowed to dry
Simple Distillation
● Used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a
mixture of liquids
● The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask
● The vapour passes through the condenser, where it cools and condenses, turning into pure liquid H2O which is collected in a
beaker
● After all the water is evaporated from the solution, only the solid solute will be left behind
Fractional distillation
● Used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)
● The solution is heated to the temperature of the substance with the lowest boiling point
● This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning
into a liquid that will be collected in a beaker
● All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
● For water and ethanol: ethanol has a boiling point of 78 ºC and water of 100 ºC. The mixture is heated until it reaches 78 ºC, at
which point the ethanol boils and distils out of the mixture and condenses into the beaker
● When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated
Paper Chromatography
● This technique is used to separate substances that have different solubilities in a given solvent (e.g. different
coloured inks that have been mixed to make black ink)
● A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this
as ink would run into the chromatogram along with the samples
● The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the
solvent so the samples don´t wash into the solvent container
● The solvent travels up the paper by capillary action, taking some of the coloured substances with it
● Different substances have different solubilities so will travel at different rates, causing the substances to spread
apart. Those substances with higher solubility will travel further than the others
● This will show the different components of the ink / dye
Assessing Purity
● Pure substances melt and boil at specific and sharp temperatures. Eg water has a boiling point of 100°C and a melting point
of 0°C
● Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different
temperatures
● Melting and boiling points data can therefore be used to distinguish pure substances from mixtures
● An unknown pure substance can be identified by experimentally determining its m.p and b.p and comparing to data tables
● Mixtures melt over a range of temperatures as they contain two or more substances
Calculation
● For chromatography to be useful the chemist needs to be able to see the components move up the paper, which is not the
case for invisible samples such as proteins
● Locating agents are substances which react with the sample and produce a coloured product which is then visible
● The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs
visible to the naked eye
What is centrifugation ?
Centrifugation is a technique used for the separation of particles from a solution
according to their size, shape, density, viscosity of the medium and rotor speed.
The particles are suspended in a liquid medium and placed in a centrifuge tube. The
tube is then placed in a rotor and spun at a define speed.
Separation through sedimentation could be done naturally with the earth gravity,
nevertheless, it would take ages. Centrifugation is making that natural process much
faster.
Rotation of the rotor about a central axis generates a centrifugal force upon the
particles in the suspension.