Separating and purifying

Question 1

What are the 3 states of matter

Answer 1

• solid
• liquid
• gas

Question 2

What are state changes?

Answer 2

Physical changes, they can be reversed

Question 3

What is is called when a substance goes form a solid to a gas?

Answer 3

Sublimation

Question 4

What is it called when you go from a gas to a solid?

Answer 4

Deposition

Question 5

What attracts particle together?

Answer 5

Weak forces of attraction

Question 6

What needs to happen to overcome weak forces of attraction during evaporation?

Answer 6

Energy must be transferred from the surroundings to the particles

Question 7

What needs to happen for attractive forces to form during freezing?

Answer 7

Energy must be transferred from the particles to the surroundings

Question 8

The composition (make-up) of a pure substance:

Answer 8

• cannot be changed

- is the same in all parts of a piece of substance

Question 9

Why can’t we use physical methods to separate pure substances?

Answer 9

It is in the same fixed composition in all its parts

Question 10

What is a mixture?

Answer 10

Elements and/or compounds that are not chemically joined together

Question 11

Do mixtures have fixed compositions?

Answer 11

No

Question 12

What happens when something melts?

Answer 12

The particles gain enough energy to overcome weak forces of. They move further and further away from each other and the solid becomes a liquid

Question 13

What temperature does a pure substance melt over?

Answer 13

The same temperature until the substance has changed state

Question 14

What is a solution?

Answer 14

A mixture made of solutes in a liquid called the solvent

Question 15

What is crystallisation?

Answer 15

Evaporating a substance to leave the solutes behind

Question 16

What does it mean if the crystals form slowly?

Answer 16

Particles have longer to form an ordered pattern and will make larger crystals

Question 17

How can risks in crystallisation be reduced?

Answer 17

-risks of spitting are reduced by :
wearing safety goggles
Removing the Bunsen burner before solution is completely dry
Use steam to evaporate the basin

Question 18

What can chromatography be used for?

Answer 18

To find out which coloured compounds the mixture contains

Question 19

How do you work out the Rf value?

Answer 19

Rf=distance moved by spot/distance moved by solvent

Question 20

What can paper chromatography be used for?

Answer 20

• distinguish between pure and impure substances
• identify substances by comparing the pattern on the chromatogram with the patterns formed by known substances
• identifying substances by calculating there Rf values

Question 21

What is the combination of evaporation followed by condensation?

Answer 21

Distillation

Question 22

What is the apparatus used in distillation called?

Answer 22

Still

Question 23

What can fractional distillation be used for?

Answer 23

• separate different products in crude oil
• make alcoholic drinks such as whisky and vodka
• separate put the gases in the air after air has been cooled and turned into a liquid

Question 24

What is desalination?

Answer 24

Producing pure water from sea water

Question 25

How do you do desalination?

Answer 25

Simple distillation

Question 26

What is chemical analysis?

Answer 26

Using chemical reactions or sensitive machines to identify and measure substances in a sample

Question 27

What does fresh water in the uk usually have in it?

Answer 27

• objects such as leaves and twigs
• small insoluble particles such as grit and silt
• soluble substances including salts, pesticides and fertilisers
• bacteria and other microorganisms that might be harmful to health

Question 28

What are the stages of purifying water?

Answer 28

• screening
• sedimentation
• filtration
• chlorination