Chemistry - States of Matter and Mixtures

Question 1

Describe the arrangement and movement of particles in a solid.

Answer 1

The particles are tightly packed together in a regular arrangement and vibrate about their fixed position.

Question 2

Describe the arrangement and movement of particles in a liquid.

Answer 2

The particles are close together but in a random arrangement.
They are able to vibrate and move around one another.

Question 3

Describe the arrangement and movement of particles in a gas.

Answer 3

The particles are separated and randomly arranged. They are free to move in any direction.

Question 4

Compare the relative energies of particles in solids, liquids and gases.

Answer 4

Particles in a solid have the least amount of energy and particles in a gas have the most energy.

Question 5

What does ‘interconversion of state’ mean?

Answer 5

When matter changes from one state to another due to changes in temperature or pressure.

Question 6

What are the names for the state changes from solid to liquid and vice versa?

Answer 6

Solid to liquid = melting
Liquid to solid = freezing

Question 7

What are the names for the state changes from liquid to gas and vice versa?

Answer 7

Liquid to gas = evaporation
Gas to liquid = condensation

Question 8

Describe the forces between particles in a solid.

Answer 8

There are strong forces of attraction between the particles, which keep them in their fixed positions.

Question 9

Describe the forces between particles in a liquid.

Answer 9

There are weaker attraction forces than in a solid so they remain held in contact but can move around each other.

Question 10

Describe the forces between particles in a gas.

Answer 10

Weakest intermolecular forces so the particles are in random arrangements and move randomly.

Question 11

How does a physical change differ from a chemical change?

Answer 11

A physical change involves changes in the forces between particles: the particles themselves and the chemical properties remain the same.

A chemical change affects the chemical properties of a substance.

Question 12

Are physical changes easily reversible?

Answer 12

Yes.

This is because no new product is formed during the changes of state.

Question 13

What is the term that describes a solid changing into a gas straight away?

Answer 13

Sublimation.

Question 14

What happens (in terms of particles) when a solid is heated and melted into a liquid?

Answer 14

As the solid is being heated,
- The particles gain thermal energy
- which is converted to kinetic energy
- so the particles vibrate more
- causing the solid to expand until the structure breaks
- becoming a liquid.

Question 15

What happens (in terms of particles) when a liquid is heated and evaporated into a gas?

Answer 15

As the liquid is being heated,
- The particles in the liquid expand
- some particles on the surface gain enough energy to overcome the intermolecular forces
- causing them to evaporate.
- At boiling point
- all particles gain enough energy to evaporate.

Question 16

A substance melts at -183 degrees and boils at -50 degrees, what state is it in at -90 degrees?

Answer 16

Liquid.

Question 17

What is a mixture?

Answer 17

Contains 2 or more elements or compounds that are NOT chemically combined.

The chemical properties of each substance in the mixture are unchanged.

Question 18

What is a pure substance?

Answer 18

A single element or compound, not mixed with any other substance.

Question 19

How can you use melting point data to distinguish between pure substances and mixtures?

Answer 19

Pure substances have a sharp and exact melting point.

Mixtures melt over a range of temperatures as they consist of several elements/compounds.

Question 20

When is simple distillation used?

Answer 20

Used to separate a solvent from a solution.

It is useful for producing water from a salt solution.

Question 21

When is fractional distillation used to separate mixtures?

Answer 21

It is used to separate a pure liquid from a mixture of liquids.

These liquids MUST have different boiling points to be separated.

Question 22

What is the difference between fractional and simple distillation?

Answer 22

Simple distillation is used to separate a solvent from a solution.

Fractional distillation is used to separate different liquids from a mixture of liquids, using their different boiling points.

Question 23

How does fractional distillation work?

Answer 23

• Oil is heated until it evaporates into the fractioning column.
• Vapours rise up the fractioning column and condense at different fractions (depending on the different boiling points).

Question 24

What sort of mixtures can filtration be used to separate?

Answer 24

Filtration is used to separate an insoluble substance from a solution.

Question 25

When is the process of crystallisation used to separate a mixture?

Answer 25

To separate a soluble solid from a solution if the solid decomposes when heated.

Question 26

What process can be used to identify substances in a mixture?

Answer 26

Chromatography.

Question 27

How does paper chromatography work to separate a mixture?

Answer 27

The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase will move up with the paper.

Compounds interact differently with each phase so will move different distances through the stationary phase meaning they will be separated.

Question 28

How does chromatography show the composition of a mixture?

Answer 28

Different coloured substances have different solubilities in the solvent and so will travel at different rates.

Question 29

Why should you use a lid when carrying out paper chromatography?

Answer 29

To prevent the solvent from evaporating.

Question 30

How would you distinguish between pure and impure substances in paper chromatography?

Answer 30

Pure substances will produce one spot.

Impure substances will produce multiple.

Question 31

What is the Rf value?

Answer 31

The ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent.

Question 32

What does potable mean?

Answer 32

Safe to drink.

Question 33

How can waste and ground water can be made potable?

Answer 33

1. Sedimentation: Large insoluble particles sink to the bottom after the water is left to sit for a while.
2. Filtration: Removes small insoluble particles by passing the water through layers of sand and filters.
3. Chlorination: Kills bacteria and microorganisms, which are too small to be removed by filtration.

Question 34

How can seawater be made potable?

Answer 34

Distillation.

• Filter to remove insoluble particles.
• Boil.
• Cool and condense the water vapour.

Question 35

What issues surround making seawater potable?

Answer 35

• Extremely expensive as a lot of energy is required to boil large volumes of water.
• Wastewater is extremely toxic due to the high concentration of salt so must be disposed of carefully.

Question 36

What is deionised water?

Answer 36

Water that has had metallic ions removed.

Question 37

why is deionised water used in experimental analysis?

Answer 37

It is used to prevent ions in the water from interacting with the substances under analysis.

If water was deionised, false positive results may be produced.