C2- Methods Of Seperating And Purifying Substances

Question 1

Tell me about the composition of a pure substance

Answer 1

It can’t be changed

It’s the same for all parts of a piece in that substance

We can’t seperate it into other substances

Question 2

What’s a mixture

Answer 2

Contains elements and/or compounds that are not chemically joined together so you can use Physicsl processes to seperate them

Does not have s fixed composition eg the air- it can change and have more
Co2 and then less

Question 3

What is a melting point

Answer 3

When the particles gain enough energy to overcome the weak forces of attraction between them

It’s a physical property (how a substance responds to forces and energy)

Question 4

Tell me about pure substance melting points

Answer 4

It’s the same and is exact

A mixture can be a range

Question 5

What can filters be used for

Answer 5

They can let smaller pieces or liquids through but trap bigger pieces or insoluble substances

Question 6

What’s a solution

Answer 6

A mixture of solutes (dissolved substances) and in a liquid (solvent)

Question 7

What’s crystallisation

Answer 7

Separating solutes from a solution by evaporating solvent to leave solutes behind

Question 8

What’s a saturated solution

Answer 8

No more solute can be dissolved in a solvent at that temperature - if more solvent evaporates or cools them some
Solute leaves the solution

Question 9

How do we filter solutions in s lab

Answer 9

A filter funnel with filter paper - the solution passes through to form filtrate and the stuff left is the residue

Question 10

Tell me about crystallisation in a lab

Answer 10

You have the filtrate , evaporating basin, boiling water, gauze and a Bunsen burner to evaporate solvent and leave crystals of solute

Question 11

What’s a risk assessment

Answer 11

The hazard of doing an experiment are identified

Question 12

How can we reduce hazards in crystallisation

Answer 12

The risks of spitting can be reduced by wearing eye protection and removing the Bunsen burner before the solution is completely dry

Question 13

What can chromatography do

Answer 13

Can be used to find out which coloured compounds a mixture contains - eg substances in oil paintings

Question 14

Tell me about paper chromatography - how are colours separated

Answer 14

It carries different substances in the mixture at different speeds so it’s seperated

Question 15

What is the solvent also known as In paper chromatography

Answer 15

Mobile phase

Question 16

What’s the paper also known as

Answer 16

Stationary phase - through which the solvent and dissolved substances move

Question 17

What’s the chromatogram

Answer 17

The paper with the seperated components

Question 18

What’s the R(little f in bottom right corner)

Rf value

Answer 18

The distance the compound has risen divided by the solvent risen

Rf= distance moved by the spot divided by the distance moved by the solvent

The value of a particular compound does not change if the chromatography conditions used remain the same

Always less than 1

Question 19

What can paper chromatography be used for

Answer 19

Distinguish between putt and impure substances

Identify substances by comparing the pattern on the chromatogram with the patterns formed by known substances

Identify substances by calculating Rf values

Question 20

What’s is simple distillation

Answer 20

The evaporation and condensation of water to purify it

Water is heated in a conical flask and the vapour travels along the delivery tube where it condenses.

Question 21

What do anti bumping granules do

Answer 21

They make liquid boil more smoothly - small bubbles of vapour form on the corners of the granules and reduce the risk of the liquid boiling over

Question 22

What’s the distillate

Answer 22

The pure substance eg pure water

Question 23

What’s fractional distillation

Answer 23

Separating 2 or more liquids

As those with lower Boiling points will evaporate more easily than others and will turn into vapour first

The first liquid to be collected contains the lowest boiling point

Question 24

What can fractional distillation be used for

Answer 24

To seperate the different products in crude oil

Make alcoholic drinks such as whisky and vodka

To seperate out the gases in air, after the air has been cooled and turned into a liquid at -200 C

Question 25

Why would a liquid with a lower boiling point reach the top of a fractionating column more quickly than one with a higher boiling point

Answer 25

At first vapour condenses when it hits the cool glass and drips back down into the flask- as the column gradually heats up there will be a temperature gradient - it will be hottest at the bottom so the fraction with the lowest boiling point will reach the top of the Column first and the vapour will then pass into the condenser

Question 26

What’s desalination

Answer 26

Producing pure water from sea water

Can be achieved using simple distillation

Question 27

How is sea water purified

Answer 27

It’s heater do the water vapour is heater leaving salts, the vapour is then condensed

Question 28

What is chemical analysis

Answer 28

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

Question 29

What are aquifers

Answer 29

Underground rocks containing ground water

Question 30

Why must the water NOT contain dissolved salts

Answer 30

They may react to form unexpected cloudy precipitates that may hide the correct result of the analysis

Machines may detect salts leading to an incorrect conclusions

Question 31

What do fresh water from sources such as river, lakes and aquifers contains

Answer 31

Objects such as leaves and twigs

Small insoluble particles such as grit and silt

Soluble substances such as salts, pesticides and fertilisers

Bacteria and other microorganisms that may be harmful to health

Question 32

What’s sedimentation

Answer 32

Allowing time for small particles To settle out

Question 33

What’s chlorination

Answer 33

It’s added to water to kill microorganisms

Question 34

Tell me how water is treated

Answer 34

Water from source is put in a sedimentation tank and then a filtration tower and then Chlorine is added and then water is stored in a tower and then distributed to homes