This were notes from different web pages, books, revised by teachers and checked with the syllabus of 2023.
These notes are for the examination of IGCSE 2023 co-ordinated science ( this is only the chemistry part).
Chemistry
C2. The States of Matter
https://www.freeexamacademy.com/revision/
Solids
● Solids have a fixed volume and shape and they
have a high density.
● The atoms vibrate in position but can’t change
location. Exam Tip
● The particles are packed very closely together in
a fixed and regular pattern. You can explain the differences in the physical
properties of solids, liquids, and gases by referring to
Liquids the arrangement and motion of particles. This is called
the kinetic theory of matter.
● Liquids adopt the shape of the container.
● They are generally less dense than solids (an
exception is a water), but much denser than
gases.
● The particles move and slide past each other
which is why they are able to flow freely.
Gases
● Gases do not have a fixed volume, and, like
liquids, take up the shape of the container.
● Gases have a very low density.
● Since there is a lot of space between the
particles, gases can be compressed into a much
smaller volume.
● The particles are far apart and move randomly
and quickly (around 500 m/s) in all directions.
● They collide with each other and with the sides
of the container (this is how pressure is created
inside a can of gas).
Diffusion
● It is the spreading of one substance (liquid or
gas)
, ● through another from a region of high This assessment of substance purity is important,
concentration to a region of low concentration especially.
due to the continuous random motion of
particles. in food consumption, as its intake can be dangerous.
Evidence for diffusion: Paper chromatography:
● In liquids: potassium manganate (VII) in a
The method used to separate substances in a solvent.
beaker of water In gases: a gas jar of air and a
gas jar of bromine connected different solubilities
Factors that affect the rate of diffusion: 1. Drop the substance onto the start line (pencil) drawn
on chromatography paper
Temperature increases → rate of diffusion increases.
2. Paper is placed in a beaker with solvent; the paper
Lower relative molecular mass→ rate of diffusion is
must. touch the surface of the solvent while the line
higher.
must be above the liquid.
This can be demonstrated in the reaction
3. Solvent travels up the paper by capillary action.
between ammonia, NH3, and hydrogen chloride
gas, HCl, inside a long glass tube. 4. Different solubilities lead to different travel rates
[high solubility-> high travel rate].
Where the two gases meet a white smoke of
ammonium chloride, NH4Cl, is formed. ● The stationary phase is the material on which
separation takes place.
This does not occur in the middle of the tube as
● The mobile phase consists of the mixture you
you might expect, but much closer to the end
want to separate, dissolved in a solvent.
with the hydrogen chloride (Mr = 36.5) and the
ammonia (Mr = 17) molecules being smaller and
lighter.
Criteria of purity
Assessing purity
Pure substances Have a definite, sharp m.p./b.p.
Impure substances Have a lower m.p and a higher b.p
, ● For a difference in solubility, a suitable solvent
must be chosen to ensure the desired substance
only dissolves in it and not other substances or
impurities, e.g. to separate a mixture of sand
and salt, water is a suitable solvent to dissolve
the salt, but not the sand.
Mixtures of liquids
● Immiscible liquids can be separated using a
separating funnel or by decanting (pouring
Interpreting simple chromatograms:
carefully).
● Chromatograms are the visual outputs on the
chromatography paper.
A number of rings/dots = a number of substances
● If two dots travel the same distance up the
paper they are the same substance.
Retention Value:
Used to identify a substance, calculated by the formula:
Locating Agents
Used to make colorless chromatograms visible
● Dry paper in the oven.
● Spray it with locating agent.
● Heat it for 10 minutes in the oven.
Exam Tip
Paper chromatography is the name given to the overall
separation technique while a chromatogram is a name Filtration
given to the visual output of a chromatography run. This
is the piece of chromatography paper with the visibly Used to separate a solid from a liquid
separated components after the run has finished.
● mixture goes through a funnel with filter paper,
Methods of purification into a flask.
● Insoluble residue remains in the funnel.
● Filtrate goes through and collects in the flask.
Mixtures of solids
● Differences in density, magnetic properties,
sublimation, and solubility can be used.
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