Describe solids, liquids and
gases in terms of the
kinetic particle theory
Solid
arrangement: fixed pattern
movement: only vibrate
proximity: close together
Liquid
arrangement: random - no fixed pattern
movement: slide past each other
proximity: close together
Gas
arrangement: random
movement: move
everywhere rapidly
proximity: far apart
Describe change of
state in terms of the
kinetic particle theory
During a change of state, energy is
absorbed (if melting or boiling -
breaking inter-molecular bonds), or
released (if condensing or freezing
- binding inter-molecular bonds)
Describe and
explain diffusion
Diffusion is the random
movement of particles in
solutions or gases leading to
complete mixing of the particles
from an area of high
concentration to areas
of less concentration
Describe how rate of
diffusion depends on
molecular mass
the speed of diffusion
depends on how
heavy the molecules
of the substance are
the greater the relative
molecular mass, the
heavier the molcule
Name apparatus for
measuring mass,
time, temperature
and volume
Mass
measured in kg
(in chemistry:
grams)
measured using a
(top pan) balance
Time
measured using
a stopwatch
Temperature
measured in degrees C
measured using a
thermometer
Volume
Volumes of liquids
measuring cylinder
volumetric flask
volumetric pipette - more accurate
burette - more accurate
Volumes of gases
gas syringe
displacement of water
Describe paper
chromatography and
interpret
chromatograms
Paper chromatography is
the separation of a mixture
of substances using filter
paper amd a solvent
Calculate Rf values
from chromatograms
Rf value = distance from base line to the centre of the spot /
distance of solvent front from the base line
Understand the use
of locating agents in
chromatography
Locating agents are used to make
colouless compounds visible on a
chromatogram. Once chromatography
has been carried out, mark a line near
the top of the paper to show where the
solvent has reached - this is the solvent
front. The chromatography paper is then
dried and sprayed with a chemical (a
locating agent) which reacts with the
chemicals in the colourless spot and a
coloured compound is formed.
Identify and assess
the purity of
substances from
melting and boiling
point data
e.g. Pure water boils at 100 degrees C exactly.
Impure water boils above 100 degrees C
depending on the concentration of the
dissolved salt (impurity)
A pure substance melts and boils at a definite temperature.
An impure substance melts and boils over a range of
temperatures.
Understand the
importance of
purity in medicines
and foodstuffs
Because we take medicines and
foodstuffs into our bodies, they
must be pure, otherwise, if there
are any unwanted substances
(impurities), they may have
harmful effects on health
Describe methods of
purification using
solvents or by filtration
or crystallisation
Filtration
Decanting
pouring off the solution
Centrifugation
A centrifuge is a machine
which spins test tubes round at
very high speeds. The spinning
pulls the solid to the bottom of
the test tube. Then decant the
liquid from the solid.
Crystallisation
Solution is heated in an
evaporating basin. The
solvent evaporates until
crystals start to form at
the bottom.
Solvent extraction
Understand the use of
simple distillation and
fractional distillation
Simple distillation is used
to separate water from a
dissolved salt. Distillation
is a combination of 2
processes: evaporation
and condensation.
Simple distillation can
be used to get drinking
water from salt water on
a large scale.
Fractional distillation is
used to separate a mixture
of liquids with different
boiling points - to separate
more volatile liquids from
less volatile liquids.
Fractional distillation is
very important for the
separation of petroleum
fractions and separating
ethanol from water.