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  Doc Brown's
Chemistry KS4 science GCSE/IGCSE Revision Notes
States of Matter
gas-liquid-solid revision notes
Part 1 The
particle model and properties of the gases, liquids and solids, state changes
and solutions
THE THREE PHYSICAL STATES OF
MATTER
GASES eg the air mixture around us
(including the oxygen needed for combustion)
and the high pressure steam in the boiler and cylinders of the steam locomotive.
All of these gases are 'invisible', being colourless and transparent, so note
that the 'steam' you see outside of the locomotive is actually fine liquid droplets of water, formed from
the expelled steam condensing when it meets the cold air - the 'state
change' of gas to liquid, same effect in mist and fog formation).
LIQUIDS eg water is the most
common example, but so are, milk, hot butter, petrol, oil, mercury or
alcohol in a thermometer.
SOLIDS eg stone, rubber of
walking boots and the majority of physical objects around you. In fact most objects
are useless unless they have a solid structure!
The basic physical properties of gases,
liquids and solids are described in terms of structure, particle movement,
effects of temperature and pressure changes, and particle models used to explain these
properties and characteristics. Hopefully, theory and fact will match up to give students a clear
understanding of the material world around them in terms of gases, liquids and
solids - referred to as the three physical states of matter. The changes of
state known as melting, fusing, boiling, evaporating, condensing, liquefying,
freezing, solidifying, crystallising are described and explained with particle
model pictures to help understanding. There is also a mention of miscible and
immiscible liquids.
GCSE/IGCSE multiple choice QUIZ on states of matter
- gases, liquids & solids
Part II Advanced
notes on gas law calculations, kinetic
model theory of an IDEAL GAS & non-ideal gases
 Sub-index for Part I sections (this page): 1.1 Three
states of matter: 1.1a gases, 1.1b liquids, 1.1c
solids * 2. State changes: 2a
evaporation and boiling, 2b condensation,
2c distillation, 2d melting, 2e
freezing, 2f cooling and heating curves and
relative energy changes,
2g sublimation * 3. Dissolving, solutions.
miscible/immiscible liquids * Appendix 1. Particle
pictures of elements, compounds & mixtures
GCSE-AS(basic) KEYWORD
index for Part I (this page):
Boiling
* Boiling point
* Brownian motion *
Changes of state *
Condensing
* Cooling
curve * Diffusion *
Dissolving * Evaporation
* Freezing
* Freezing
point * Gas particle picture
* Heating curve
* Liquid particle picture
* Melting
* Melting
point *
miscible/immiscible liquids * Particle
pictures of elements, compounds & mixtures * Properties of gases
* Properties of liquids
* Properties of solids
* solutions
* sublimation * Solid particle picture
Sub-index for Part II (on separate Advanced page):
Section 4 Ideal gas behaviour and the gas laws:
Introduction-the kinetic
particle theory of an ideal gas
* 4a. Boyle's Law *
4b. Charles's-Gay Lussac's Law and the combined gas law equation
* 4c. The ideal gas equation PV=nRT * 4d. Dalton's Law of partial pressures
* 4e. Graham's Law of diffusion *
Section 5. Non-ideal real gas behaviour and Van der Waals Equation:
5a. The deviations of a gases from ideal
behaviour and their causes * 5b.
The Van der Waals equation of state
* 5c Compressibility factors * 5d
The
Critical Point - The Critical Temperature and Critical Pressure *
1.1. The Three States of Matter, gas-liquid-solid particle theory models
-
WHAT ARE THE THREE STATES OF MATTER?
-
WHY ARE THEY LIKE WHAT THEY ARE?
-
HOW CAN WE EXPLAIN HOW THEY BEHAVE?
-
CAN PARTICLE MODELS HELP US UNDERSTAND THEIR
PROPERTIES and CHARACTERISTICS?
-
WHY IS IT IMPORTANT TO
KNOW THE PROPERTIES OF GASES, LIQUIDS AND SOLIDS?
-
CAN WE MAKE
PREDICTIONS BASED ON THEIR CHARACTERISTIC PROPERTIES?
-
This page introduces general
physical descriptions of substances in the simplest physical (non-chemical) classification level
i.e. is it a gas, liquid or a solid.
-
BUT, this web page also introduces 'particle models' in which
a small circle represents an atom or a molecule i.e. a particular particle
or simplest unit of a substance.
-
This section is quite
abstract in a way because you are talking about particles you can't
see as individually, you just the 'bulk' material and its physical
character and properties.
 1.1a.
The particle model of a Gas
- WHAT IS THE
GASEOUS STATE OF MATTER?
- WHAT ARE THE
PROPERTIES OF A GAS?
- HOW DO GASEOUS
PARTICLES BEHAVE?
- A gas has no fixed shape or volume, but always spreads out
to fill any container.
- There are a
lmost no forces of attraction between the particles
so they are completely free of each other.
The particles are widely spaced and scattered at random throughout the container so there is no order in the system.
The particles move rapidly in all directions,
frequently colliding with each other and the side of the container.
With increase in temperature, the particles move faster as they gain kinetic
energy.
Using the particle model to explain the properties of a Gas
Gases have a very low density
(‘light’) because the particles are so spaced out in the container (density = mass
/ volume).
- Density order: solid > liquid
>>> gases
Gases flow freely because there are no effective forces of attraction between the
gaseous particles - molecules.
- Ease of flow order: gases >
liquids >>> solids (no real flow in solid unless you powder
it!)
- Because of this gases and liquids are described as
fluids.
Gases have no surface, and no fixed shape or
volume, and because of lack of particle attraction, they
always spread out and fill any container (so gas volume = container volume).
Gases are readily compressed because of the ‘empty’ space between the particles.
- Ease of compression order: gases
>>> liquids > solids (almost impossible to compress a
solid)
Gas pressure
- When a gas is confined in a container the particles will cause and exert a
gas pressure which is measured in atmospheres (atm) or Pascals (Pa = N/m2)
- pressure is force/area on which force is exerted.
- The gas pressure is caused by the force created by millions of impacts of
the tiny individual gas particles on the sides of a container.
- For example - if the number of gaseous particles in a container is doubled, the gas
pressure is doubled because doubling the number of molecules doubles the
number of impacts on the side of the container so the total impact force per
unit area is also doubled.
- This doubling of the particle impacts doubling the pressure is pictured in
the two diagrams below.
-
If the volume of a sealed container is kept constant and the gas inside
is heated to a higher temperature, the gas pressure increases.
- The reason for this is that as the particles are heated they gain kinetic
energy and on average move faster.
- Therefore they will collide with the sides of the container with a
greater force of impact, so increasing the pressure.
- There is also a greater frequency of collision with the sides of the
container BUT this is a minor factor compared to the effect of increased kinetic
energy and the increase in the average force of impact.
- Therefore a fixed amount of gas in a sealed container of constant volume,
the higher the temperature the greater the pressure and the lower the
temperature the lesser the pressure.
- For gas pressure-temperature
calculations see Part 2 Charles's/Gay-Lussac's Law
- If the ‘container’ volume can change, gases readily expand* on heating because of the lack of particle attraction, and
readily contract on cooling.
- On heating, gas particles gain kinetic energy,
move faster and hit the sides of the container more frequently, and
significantly, they hit with a greater force.
- Depending on the container situation, either or both of the pressure or volume will increase (reverse on cooling).
- Note: *
It is the gas volume that expands NOT the molecules, they stay the same
size!
- If there is no volume restriction
the expansion on heating is much greater for gases than liquids or solids
because there is no significant attraction between gaseous particles. The
increased average kinetic energy will make the gas pressure rise and so
the gas will try to expand in volume if allowed to e.g. balloons in a warm
room are significantly bigger than the same balloon in a cold room!
- For gas volume-temperature calculations
see Part 2 Charles's/Gay-Lussac's Law
DIFFUSION in Gases:
- The natural
rapid and random movement of the particles in
all directions means that gases readily ‘spread’ or
diffuse.
- The net movement of a particular gas will be in the direction
from lower concentration to a higher concentration, down the so-called diffusion gradient.
- Di
ffusion
continues until the concentrations are uniform throughout the container of
gases, but ALL the particles keep moving with their ever present kinetic energy!
Diffusion is faster in gases than
liquids where there is more space for them to move
(experiment illustrated below) and
diffusion is negligible in solids due to the close packing of the particles.
- Diffusion is responsible for the
spread of odours even without any air disturbance e.g. use of perfume,
opening a jar of coffee or the smell of petrol around a garage.
- The rate of diffusion increases with increase in temperature as the particles
gain kinetic energy and move faster.
- Other evidence for random particle
movement including diffusion:
- When smoke particles are viewed under a
microscope they appear to 'dance around' when illuminated with a light
beam at 90o to the viewing direction. This is because the
smoke particles show up by reflected light and 'dance' due to the
millions of random hits from the fast moving air molecules. This is
called 'Brownian motion' (see
below in liquids). At any given instant of time,
the hits will not be even, so the smoke particle get a greater bashing
in a random direction.
 - A two gaseous molecule
diffusion experiment is illustrated above and explained below!
- A long glass tube (2-4 cm diameter) is filled at one
end with a plug of cotton wool soaked in conc. hydrochloric acid
sealed in with a rubber bung (for health and safety!). A similar plug of
conc. ammonia solution
is placed at the other end. The soaked cotton wool plugs will give off
fumes of HCl
and NH3 respectively,
and if the tube is left
undisturbed and horizontal, despite the lack of tube movement, e.g. NO
shaking to mix and the absence of convection, a white cloud forms about
1/3rd
along from the conc. hydrochloric acid tube end.
- Explanation: What happens is the colourless
gases, ammonia and hydrogen chloride, diffuse down the tube and
react to form fine white crystals of the salt ammonium chloride.
- ammonia
+ hydrogen chloride
==> ammonium
chloride
- NH3(g) + HCl(g)
==> NH4Cl(s)
-
Note the rule: The smaller the
molecular mass, the greater the average speed of the molecules
(but all gases have the same average kinetic energy at the same
temperature).
- Therefore the smaller the
molecular mass, the faster the gas diffuses.
- e.g. Mr(NH3)
= 14 + 1x3 = 17, moves faster
than Mr(HCl) =
1 + 35.5 = 36.5
- AND that's why they meet nearer
the HCl end of the tube!
- So the experiment is not only evidence
for molecule movement, it is also evidence that molecules
of different
molecular masses move/diffuse at different speeds.
- For a mathematical
treatment see Graham's Law of Diffusion
 A
coloured
gas, heavier than air (greater density), is put into the
bottom gas jar and a second gas jar of lower density colourless air is placed over it separated with a
glass cover.If the glass cover is removed
then (i) the colourless air gases diffuses down into the coloured brown
gas and (ii) bromine diffuses up into the air. The particle movement
leading to mixing cannot be due to convection because the more dense gas starts at the
bottom!
No 'shaking' or other means of mixing is required. The
random movement of both lots of particles is enough to ensure that both gases
eventually become completely mixed by diffusion.
This is clear evidence for diffusion
due to the random continuous movement of all the gas particles and,
initially, the net movement of one type of particle from a higher to a
lower concentration ('down a diffusion gradient'). When fully mixed, no further colour change
distribution is observed BUT the random particle movement continues! See
also other evidence in the liquid section below.
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A note on 'forces'
1.1b.
The particle model of a Liquid
WHAT IS THE LIQUID
STATE OF MATTER?
WHAT ARE THE
PROPERTIES OF A LIQUID?
HOW DO LIQUID
PARTICLES BEHAVE?A liquid has a fixed volume at a given temperature but
its shape is that of the container which holds the liquid.
There are much greater forces of attraction between the particles in a liquid compared to
gases, but not quite as much as in solids.
Particles quite close together but still arranged at random throughout the container, there is a little close range order as you can get clumps of particles clinging together temporarily.Particles moving rapidly in all directions but
more frequently collisions with each other than in gases due to
shorter distances between particles.
With increase in temperature, the particles
move faster as they gain kinetic energy, so increased
collision rates, increased collision energy and increased rate of diffusion.
Using the particle model to explain the properties of a Liquid
- Liquids have a much greater density than gases (‘heavier’) because the particles are much closer
together because of the attractive forces.
Most liquids are just a little less dense than when they are
solid
- Water is a curious exception to this general rule, which is
why ice floats on water.
Liquids usually flow freely
despite the forces of attraction between the particles but liquids are not as ‘fluid’ as gases.
- Note 'sticky' or viscous liquids have much stronger attractive forces between
the molecules BUT not strong enough to form a solid.
Liquids have a surface, and a fixed volume (at a particular temperature) because of the increased particle attraction, but the shape is not fixed and is merely that of the container itself.
- Liquids seem to have a very weak 'skin' surface effect which is caused by
the bulk molecules attracting the surface molecules disproportionately.
Liquids are not readily compressed because
there is so little ‘empty’ space between the particles, so increase in pressure
has only a tiny effect on the volume of a solid, and you need a huge increase in
pressure to see any real contraction in the volume of a liquid.
Liquids will expand on heating but nothing like as much as gases because of the greater particle attraction restricting the
expansion (will contract on cooling).
- Note: When heated, the liquid particles gain kinetic energy and hit the sides of the container more frequently, and more significantly, they hit with a greater force, so in a sealed container the pressure produced can be considerable!
The natural rapid and random movement of the particles means that liquids ‘spread’ or
diffuse. Diffusion is much slower in liquids compared to gases because there is less space for
the particles to move in and more ‘blocking’ collisions happen.
- Just dropping lumps/granules/powder of a soluble solid (preferably
coloured!) will resulting in a dissolving followed by an observable diffusion
effect.
- Again, the net flow of dissolved particles will be from a higher
concentration to a lower concentration until the concentration is uniform
throughout the container.
Diffusion in liquids - evidence for random particle movement in
liquids:
- If coloured crystals of e.g. the highly
coloured salt crystals of potassium manganate(VII) are dropped into a
beaker of water and covered at room temperature.
- Despite the lack of
mixing due to shaking or convection currents from a heat source etc. the bright purple colour of the dissolving salt
slowly spreads throughout all of the liquid but it is much slower than the
gas experiment described above because
of the much greater density of particles slowing the spreading due to close
proximity collisions.
- The same thing happens with dropping
copper sulphate crystals (blue, so observable) or coffee granules into water and just leaving the
mixture to stand.
- When pollen grains are viewed under a
microscope they appear to 'dance around' when illuminated with a light
beam at 90o to the viewing direction.
- This is because the
pollen grains show up by reflected light and 'dance' due to the
millions of random hits from the fast moving water molecules.
- This phenomenon is
called 'Brownian motion' after a
botanist called Brown first described the effect (see
gases above).
- At any given instant of time,
the hits will not be even all round the pollen grain, so they get a greater
number of hits in a random direction.
1.1c.
The particle model of a Solid
WHAT IS THE SOLID
STATE OF MATTER?
WHAT ARE THE
PROPERTIES OF A SOLID?
HOW DO SOLID
PARTICLES BEHAVE?A solid has a fixed volume and shape at a particular
temperature unless physically subjected to some force.
The greatest forces of attraction are between the particles in a solid and they pack together as tightly as possible in a neat and ordered arrangement.
The particles are too strongly held together to allow movement from place to place but the particles vibrate about their position in the structure.
With increase in temperature, the particles vibrate faster and more strongly as they gain kinetic energy.
Using the particle model to explain the properties of a Solid
- Solids have the greatest density (‘heaviest’) because the particles are closest together.
- Solids cannot flow freely like gases or liquids because the particles are strongly held in fixed positions.
- Solids have a fixed surface and volume (at a particular temperature) because of the strong particle attraction.
- Solids are extremely difficult to compress because there is no real ‘empty’ space between the particles,
so increase in pressure has virtually no effect on the volume of a solid.
- Solids will expand a little on heating but nothing like as much as liquids because of the greater particle attraction restricting the expansion
and contraction occurs on cooling.
- The expansion is caused by the increased
energy of particle vibration, forcing them further apart causing an
increase in volume and corresponding decrease in density.
- Diffusion is almost impossible in solids because the particles are too
closely packed and strongly held together with no ‘empty space’ for particles to move
through.
2. Changes of State
for gas <=> liquid <=> solid
A change of state means an interconversion
between two states of matter, namely gas <=> liquid <=> solid
e.g. solid ==> liquid is melting or fusing
liquid ==> gas/vapour (vapor) is boiling,
evaporation or vapourisation (vaporisation)
and the reverse processes
gas/vapour (vapor) ==> liquid is condensation,
liquefaction/liquefying
liquid ==> solid is freezing, solidifying or
crystallising
and there is also
solid ==> gas is sublimation
We can use the state particle models and diagrams to explain changes of state and the energy changes involved.
These are NOT chemical changes BUT PHYSICAL CHANGES, e.g.
the water molecules H2O are just the same in ice, liquid water, steam
or water vapour. What is different, is how they are arranged, and how strongly
they are held together by intermolecular forces in the solid, liquid and gaseous
states.
2a.
Evaporation and Boiling (liquid to gas)
- On heating particles gain kinetic energy
and move faster and more able to overcome the intermolecular forces
between the molecules i.e. some particles will have enough kinetic energy to
overcome the attractive forces holding the particles together in the bulk
liquid.
- In evaporation* and boiling it is the
highest kinetic energy molecules that can ‘escape’ from the attractive forces of the other liquid particles.
- The particles lose any order and
become completely
free to form a gas or vapour.
- Energy is needed to overcome the attractive forces
between particles in the liquid and is taken in from the surroundings.
- This means heat is taken in,
so evaporation and boiling are endothermic processes
(ΔH +ve).
- If the temperature is high enough boiling
takes place.
- Boiling is rapid evaporation
anywhere in the bulk liquid
and at a fixed temperature called the boiling point and requires continuous addition of heat.
- The rate of boiling is limited by the rate
of heat transfer into the liquid.
- * Evaporation takes place more slowly
than boiling
at any temperature between the melting point and boiling point,
and only from the
surface, and results in the liquid becoming cooler due to
loss of higher kinetic energy particles.
- More details on the e
nergy changes for these physical changes of state
for a range of substances are dealt with in a section of
the Energetics Notes.
2b.
Condensing (gas to liquid)
- On cooling, gas particles lose kinetic energy and eventually become attracted together to form a liquid
i.e. they haven't enough kinetic energy to remain free in the gaseous state.
- There is an increase in order as the particles are much closer together and can form clumps of molecules.
- The process requires heat to be lost to the surroundings i.e. heat given out, so
condensation is exothermic (ΔH -ve).
- This is why steam has such a scalding
effect, its not just hot, but you get extra heat transfer to your skin
due to the exothermic condensation on your surface!
2c. Distillation
2d.
Melting (solid to liquid)
- When a solid is heated the particles vibrate more strongly
as they gain kinetic energy and the particle attractive forces are weakened.
- Eventually, at the melting point, the attractive forces are too weak to hold the
particles in the structure together in an ordered way and so the solid melts.
- Note that the intermolecular forces are still there to hold the bulk
liquid together - but the effect is not strong enough to form an ordered
crystal lattice of a solid.
The particles become free to move around and lose their ordered arrangement.
Energy is needed to overcome the attractive forces and give
the particles increased kinetic energy of vibration.
So heat is taken in from the surroundings and
melting is an endothermic process (ΔH +ve).
Energy changes for these physical changes of state
for a range of substances are dealt with in a section of
the Energetics Notes.
- On cooling, liquid particles lose kinetic energy and so can
become more strongly attracted to each other.
When the temperature is low enough, the kinetic energy of the particles is
insufficient to prevent the particle attractive forces causing a solid to
form.
Eventually at the freezing point the forces of attraction are sufficient to remove any remaining freedom
of movement (in terms of one place to another) and the particles come together to form the ordered solid arrangement
(though the particles still have vibrational kinetic energy.
Since heat must be removed to the surroundings,
so strange as it may seem,
freezing is an exothermic process (ΔH -ve).
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2f.
Cooling and Heating Curves
and the comparative energy changes of state changes gas <=>
liquid <=> solid |
2f(i)
Cooling curve:
Note the temperature stays constant during the state changes of condensing
at temperature Tc, and freezing/solidifying at temperature Tf.
This is because all the heat energy removed on cooling at these temperatures
(the
latent heats or enthalpies of state change), allows
the strengthening of the inter-particle forces without temperature fall (the
heat loss is compensated by the exothermic increased intermolecular
force attraction).
In between the 'horizontal' state change sections of the graph, you can
see the energy 'removal' reduces the kinetic energy of the particles,
lowering the temperature of the substance.
A cooling curve summarises the changes:
gas ==> liquid
==> solid
Energy changes
for these physical changes of state for a range of substances are dealt with in a section of
the Energetics Notes.
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2f(ii)
Heating curve:
Note the temperature stays constant during the state changes of melting
at temperature Tm and boiling at temperature Tb. This is because all the energy absorbed in
heating at these temperatures
(the latent heats or enthalpies of state change),
goes into weakening the inter-particle
forces without temperature rise
(the heat gain equals the endothermic/heat absorbed energy required to
reduce the intermolecular forces). In between the 'horizontal' state change
sections of the graph, you can see the energy input increases the
kinetic energy of the particles and raising the temperature of the
substance.
A heating curve summarises the changes:
solid
==> liquid ==> gas
Energy changes
for these physical changes of state for a range of substances are dealt with in a section of
the Energetics Notes.
|
2g.
Sublimation
-
This
is when a
solid, on heating, directly changes into a gas without melting, AND the
gas on cooling re-forms a solid directly without condensing to a
liquid. They usually involve
just a physical change BUT its not always that simple!
Theory in terms of particles:
-
When the solid is heated
the particles vibrate with increasing force from the added thermal
energy.
-
If the particles have enough kinetic energy of vibration to
partially overcome the particle-particle attractive forces you would
expect the solid to melt.
-
HOWEVER, if the particles at this point have
enough energy at this point that would have led to boiling, the liquid
will NOT form and the solid turns directly into a gas.
-
On cooling, the particles
move slower and have less kinetic energy.
-
Eventually, when the particle kinetic energy is low
enough, it will allow the particle-particle attractive forces to produce
a liquid.
-
BUT the energy may be low enough to permit direct formation of
the solid, i.e. the particles do NOT have enough kinetic energy to
maintain a liquid state!
Examples:
-
Even at room temperature
bottles of solid iodine show crystals forming at the top of the bottle
above the solid. The warmer the laboratory, the more crystals form when
it cools down at night!
The formation of a particular
form of
frost involves the direct freezing of water vapour (gas).
Frost can also evaporate directly back to water vapour (gas) and this
happens in the 'dry' and extremely cold winters of the Gobi Desert on a
sunny day.
Solid carbon dioxide (dry ice)
is
formed on cooling the gas down to less than -78oC. On warming
it changes directly to a very cold gas!, condensing any water vapour in
the air to a 'mist', hence its use in stage effects.
- CO2
(s)
CO2 (g) (physical change only)
On heating strongly in a test tube, the
white solid ammonium chloride, decomposes into a mixture of two
colourless gases ammonia and hydrogen chloride. On
cooling the reaction is reversed and solid ammonium chloride reforms at
the cooler top of the test tube.
+
heat energy
ammonia + hydrogen chloride
NH4Cl(s)
NH3(g) + HCl(g)
This involves both chemical and
physical changes and is so is more complicated than examples 1. to 3. In
fact the ionic ammonium chloride crystals change into covalent
ammonia and hydrogen chloride gases which are naturally far more
volatile (covalent substances generally have much lower melting and
boiling points than ionic substances).
The liquid particle picture
does not figure here, but the other models fully apply apart from state
changes involving liquid formation. GAS
particle model and SOLID
particle model links.
PLEASE NOTE, At a higher
level of study (e.g. UK A2 advanced level),
you need to study
the g-l-s phase diagram for water and the vapour pressure curve of ice at
particular temperatures. For example, if the ambient vapour
pressure is less than the equilibrium vapour pressure at the temperature of
the ice, sublimation can readily take place. The snow and ice in the Gobi
Desert do not melt in the Sun, they just slowly 'sublimely' disappear!
3. Dissolving
solids, solutions and miscible/immiscible liquids
-
3a.
WHAT HAPPENS TO PARTICLES WHEN A
SOLID DISSOLVES IN A LIQUID SOLVENT? -
WHAT DO THE WORDS
SOLVENT, SOLUTE AND SOLVENT MEAN?
When a solid (the
solute) dissolves in a liquid (the solvent) the resulting mixture is
called a solution.
-
In general: solute +
solvent ==> solution
-
The solid loses all its
regular structure and the individual solid particles (molecules or ions) are
now completely free from each other and randomly mix with the
original liquid particles, and all particles can move around at random.
-
This describes salt
dissolving in water, sugar dissolving in tea or wax dissolving in a
hydrocarbon solvent like white spirit.
-
It does not usually
involve a chemical reaction, so it is generally an example of a physical
change.
-
Whatever the changes in
volume of the solid + liquid, compared to the final solution, the Law of
Conservation of Mass applies.
-
This means: mass of
solid solute + mass of liquid solvent = mass of solution
-
You cannot make mass
or lose mass, but just change it into another form.
-
If the solvent is
evaporated, then the solid is reformed e.g. if a salt solution is left
out for a long time or gently heated to speed things up, eventually salt
crystals form, the process is called crystallisation.
3b.
WHAT HAPPENS TO PARTICLES WHEN
TWO LIQUIDS COMPLETELY MIX WITH EACH OTHER?
WHAT DOES THE WORD
MISCIBLE MEAN?
If two liquids completely
mix in terms of their particles, they are called miscible liquids
because they fully dissolve in each other. This is shown in the diagram below
where the particles completely mix and move at random. The process can be
reversed by
fractional distillation.
3c.
WHAT HAPPENS TO PARTICLES WHEN
TWO LIQUIDS DO NOT MIX WITH EACH OTHER?
WHAT DOES THE WORD
IMMISCIBLE MEAN?
WHY DO THE LIQUIDS
NOT MIX?
If the two liquids do NOT
mix, they form two separate layers and are known as
immiscible liquids,
illustrated in the diagram below where the lower purple liquid will be more
dense than the upper layer of the green liquid.
-
You can separate these two
liquids using a separating funnel.
-
The reason for this is that the
interaction between the molecules of one of the liquids alone is stronger
than the interaction between the two different molecules of the different
liquids.
-
For example, the force of attraction between water molecules is
much greater than either oil-oil molecules or oil-water molecules, so two
separate layers form because the water molecules, in terms of energy change,
are favoured by 'sticking together'.
 |
 |
3d. How a separating
funnel is used
1.
The mixture is put in the separating funnel with the stopper on and the
tap closed and the layers left to settle out.
2.
The stopper is removed, and the tap is opened so that you can carefully
run the lower grey layer off first into a beaker.
3. This leaves behind the upper yellow layer
liquid, so separating the two immiscible liquids. |
keywords-phrases: GASES, LIQUIDS, SOLIDS, States of Matter,
particle models, theory of state changes, melting, boiling, evaporation,
condensing, freezing, solidifying, cooling curves, 1.1 Three states of matter: 1.1a gases,
1.1b liquids, 1.1c solids * 2. State changes: 2a evaporation and boiling, 2b
condensation, 2c distillation, 2d melting, 2e freezing, 2f cooling and
heating curves and relative energy changes, 2g sublimation * 3. Dissolving,
solutions. miscible/immiscible liquids Boiling * Boiling point * Brownian
motion * Changes of state * Condensing * Cooling curve * Diffusion *
Dissolving * Evaporation * Freezing * Freezing point * Gas particle picture
* Heating curve * Liquid particle picture * Melting * Melting point *
miscible/immiscible liquids * Properties of gases * Properties of liquids
* Properties of solids * solutions * sublimation * Solid particle picture *
GCSE/IGCSE multiple choice QUIZ on states of matter gases liquids solids
practice revision questionsRevision KS4 Science GCSE/IGCSE/O level
Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel
GCSE Science/IGCSE Chemistry & OCR 21st Century Science, OCR Gateway Science
WJEC gcse science chemistry CCEA/CEA gcse science chemistry O Level
Chemistry (revise courses equal to US grade 8, grade 9
grade 10) science chemistry courses revision guides
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QCA 7G
"Particle model of solids, liquids and
gases"
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