Topic 2 - States of Matter and Mixtures✅

Describe the arrangement, movement and relative energy of particles in a solid

• Particles are regularly arranged

• Close together

• Vibrate about a fixed point

• Low energy

Describe the arrangement, movement and relative energy of particles in a liquid

• Particles are randomly arranged

• Close together

• Slide over each other

• Greater energy

Describe the arrangement, movement and relative energy of particles in a gas

• Particles are randomly arranged

• Far apart

• Can move quickly in all directions

• Highest energy

Name the interconversions between the states of matter

• Solid -> liquid = melting

• Liquid -> solid = freezing

• Liquid -> gas = boiling / evaporating

• Gas -> liquid = condensing

• Gas -> solid = deposition

• Solid -> gas = sublimation

What type of reaction are the interconversions between the states of matter

They are physical changes, not chemical reactions

What happens to particles when melting, evaporating and boiling occurs

• Particles gain energy

• Energy is used to break some of the bonds between particles during melting

• Energy is used to break all of the bonds between particles during evaporating or boiling

What happens to particles when condensing and freezing occurs

• Energy is transferred from a substance to the environment

• Particles lose energy as bonds form between them

What does 'pure' mean in chemistry

'Pure' in chemistry indicates a substance made from one single element or compound

What does 'pure' mean in everyday use

A pure substance is one that has nothing added to it - in its natural state

How can we use melting point data to distinguish between pure and impure substances

• Pure substances melt at a specific temperature / have a sharp boiling point

• Mixtures melt over a range of temperatures

What types of mixtures can be separated by simple distillation

A liquid from a solution

Explain simple distillation with seawater

• Pour sample of seawater into distillation flask

• Heat distillation flask.

• The part of the solution that has the lowest boiling point will evaporate (water)

• The water vapour passes into the condenser where it cools and condenses

• It then flows back into the beaker where it is collected.

• Eventually you will end up with just salt in the flask.

What types of mixtures can be separated by fractional distillation

A mixture of liquids with different boiling points

Explain fractional distillation

• Put the mixture into a flask.

• Gradually heat the flask.

• The different liquids will all have different boiling points so they will evaporate at different temperatures.

• The liquid with the lowest boiling point evaporates first.

• When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column.

• Liquids with higher boiling points will also start to evaporate

• but the column is cooler towards the top, so they will only get part of the way before condensing and running back down towards the flask.

• When the first liquid has been collected, raise the temperature until the next one reaches the top.

What types of mixtures can be separated by filtration

an insoluble solid from a liquid

Explain filtration

• Put filter paper into a funnel and pour the mixture in.

• The liquid part of the mixture runs through the paper, leaving behind a solid residue.

What types of mixtures can be separated by crystallisation

a soluble solid from a solution

Explain crystallisation

• Pour the solution into an evaporating dish and heat the solution.

• Some of the water will evaporate and the solution will get more concentrated.

• Once some of the water has evaporated or when you see crystals start to form remove the dish and leave the solution to cool.

• The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.

• Filter the crystals out of the solution and leave them in a warm place to dry.

What types of mixtures can be separated by paper chromatography

a mixture of soluble substances and identify them

Describe paper chromatography

• The separation of mixtures of soluble substances

• By running a solvent (mobile phase) through the mixture on the paper (stationary phase)

• Which causes substances to move at different rates over the paper

How to work out Rf value

distance travelled by substance divided by distance travelled by solvent

How can you tell if a substance is pure from a chromatogram?

If there is only one spot on the paper

How to interpret a paper chromatogram to identify substances by comparison with known substances

• Carry out paper chromatography with both the known substance and substance you’re testing on the same paper.

• If both spots are at the same height up the paper at the end then you know the substance you’re testing is the same as the known substance.

Explain paper chromatography

• Draw a line near the bottom of the paper (the baseline) and use a pencil (as pencil marks are insoluble).

• Put a sport of mixture to be separated on the line.

• Put some of the solvent into a beaker.

• Dip the bottom of the paper (but not the spot) into the solvent.

• the solvent will start to move up the paper.

• When the chemicals in the mixture dissolve in the solvent, they will move up the paper too.

• You will see the different chemicals in the sample separate out, forming spots at different places on the paper (if one of the components is insoluble it will not move - stay on the baseline

• Remove the paper from the beaker before the solvent reaches the top and mark the distance the solvent has moved

What is potable water

• Water suitable for drinking

• Low levels of microbes and contaminating substances

What are the ways that water be made potable

Sedimentation

• Large insoluble particles sink to the bottom of the water

Filtration

• Water is filtered through beds of sand which remove small insoluble particles

Chlorination

• Chlorine gas is put through water to kill microbes

Describe how sea water can be made potable

Distillation:

• Sea water is heated until it boils

• Salt remains in liquid, and steam is pure water

• Steam is cooled and condensed to make potable water

Why must water used in analysis not contain any dissolved salts

• Water used in analysis must be pure

• Because dissolved salts could react with the substances you are analysing, leading to a false result