C2.1 - Separation techniques -

Question 1

Filtration equipment

Answer 1

Filter paper, funnel, residue, conical flask, filtrate

Question 2

How does filtration work

Answer 2

• filtration separates an insoluble substance in the solid state from substances in the liquid state
• it works because filter paper has tiny, microscopic holes
• when you filter a mixture of sand and water, water molecules are small enough to pass through the filter paper, but the larger grains of insoluble sand cannot
• the sand stays behind in the filter paper as the residue while the water passes through as the filtrate
• particles of a dissolved solute are also small enough to pass through filter paper

Question 3

3 things that could happen when heating solution

Answer 3

• if you heat a solution, the solvent evaporates leaving the solute behind
• if you heat the solution too strongly, you get a powder
• if you allow the solvent to evaporate slowly, you get regularly shaped crystals

Question 4

How crystallisation works

Answer 4

• heat the solution until it becomes a saturated solution
  — - a solution is saturated when no more solute can be dissolved at that temperature
• crystals will start forming at this point, so let the solution cool slowly
• as the solution cools, the solubility of the solute decreases, so more crystals form
• separate them from the remaining solution by filtration, and dry them in a warm oven or by patting them with filter paper

Question 5

What simple distillation does (simple)

Answer 5

Separates a solvent from a solution

Question 6

How simple distillation works

Answer 6

• it relies on the solvent having a much lower boiling point than the solute
• when the solution is heated, the solvent boils but the solute does not
• the solvent escapes from the solution in its gas state
• it is then cooled and condensed back to its liquid state by a condenser, a piece of apparatus that is kept cold using a flow of cold water

Question 7

Tap water contains dissolved salts.

What happens during simple distraction of tap water.

Answer 7

• water vapour escapes from the tap water, leaving the dissolved salts behind

Question 8

What fractional distillation does (simply)

Answer 8

Separates two or more substances from a mixture in the liquid state

Question 9

What fractional distillation relies on and uses

Answer 9

• it relies on each substance having a different point and uses a piece of equipment called a fractionating column

Question 10

During fractional distillation of an ethanol-water mixture, ethanol vapour and water vapour both leave the liquid mixture.

In the fracturing column: (3)

In the condenser: (2)

Answer 10

In the FC:

• the vapours condense on the inside surface, heating it up
• when the temperature reaches the BP, ethanol vapour cannot condense any more, but water vapour can
• water droplets fall back into the flaks, and ethanol vapour passes into the condenser

In the C, the ethanol vapour is cooled and condensed back to its liquid state.
It drips into the collecting container.

Question 11

Each substance separated by fractional distillation is called? + why

Answer 11

• a fraction

- because it is just part of the original mixture

Question 12

Importance of the fractionating column (1)
And its features (1)
And what happens (1)

Answer 12

• you could carry out fractional distillation without the fractionating column
• however, the fractionating column improves the separation of the mixture
• it has a large SA on which the vapours can continually condense
• during fractional d. , the column becomes hottest at the bottom and coolest at the top

Question 13

Chromatography relies on 2 different chemical phases

Answer 13

Stationary phase - does not move

Mobile phase - does move

Question 14

A phase is?

Answer 14

A substance in the solid, liquid, or gas state

Question 15

Phases in paper chromatography ?

Answer 15

Stationary = absorbent paper 
Mobile = a solvent in the liquid state, such as water or propanone

Question 16

Thin layer chromatography - phases

Answer 16

stationary = thin layer of of silica or alumina powder spread over a plate of glass or plastic

Question 17

Thing layer chromatogram to separate a sample into its components for identification of analysis: (steps)

Answer 17

1 - put the solvent into a chromatography tank to a depth of about 1cm. If the solvent is flammable, make sure that there are no naked flames, and that the room is well ventilated.
2 - add a small amount of the sample to the baseline, taking care not to damage the powder on the plate
3 - let the solvent travel through the powder, and take the plate out before it reaches the top
4 - analyse the pattern of coloured spots, which is called a chromatogram

Question 18

Tell me about the pattern produced in TLC (3)

Answer 18

• The pattern produced depends on how each component is distributed between the two phases
• a component travels further up the plate if it forms stronger bonds with the mobile phase than with the stationary phase
• a component will not travel very far if it forms stronger bonds with the stationary phase than with the mobile phase

Question 19

What scientists use to compare spots on a chromatogram - and what this means - and what is it

Answer 19

• scientists use Rf values to compare spots on a chromatogram
• if two spots have the same Rf value and are the same colour, they are likely to be identical

Distance travelled by substance / distance travelled by solvent

Question 20

Rf values - range ? Units?

Answer 20

Vary from 0 to 1

Have no units

Question 21

Gas chromatography - phases

Answer 21

Stationary = silica or alumina powder packed into a metal column

Mobile = unreactive carrier gas such as nitrogen, which does jot react with the sample

Question 22

What (2) does gas chromatography do?

Answer 22

• separates the components of a mixture, and also measures their amounts

Question 23

How gas chromatography works - 5

Answer 23

• the sample is turned into the gas state when it is injected into the column
• the carrier gas pushes the sample through the column
• the different components take different times to travel through the column, depending on how strongly they bond to the stationary phase
• a detector sends a signal to a computer as each component leaves the column
• the computer produces a chromatogram in which each component is a peak plotted against the travel time

Question 24

How to tell if a substance is pure?

Answer 24

Use paper or thin-layer chromatography

Question 25

4 advantages - TLC over paper

Answer 25

- quicker - more sensitive, so a smaller sample can be used - there is a lager range of stationary phases and solvents to choose from - you can also scrape an individual spot from a thin-layer chromatogram for further analysis, for example by gas chromatography

Question 26

Separation method? Mixture contains: Insoluble and soluble substances

Answer 26

Dissolving followed by filtration

Question 27

Separation method: Mixture contains: A solute dissolved in a solvent (a solution)

Answer 27

Crystallisation to obtain the solute, | Simple distillation to obtain the solvent

Question 28

Separation method: Mixture contains: Two or more substances in the liquid state

Answer 28

Fractional distillation

Question 29

Separation method: Mixture contains: Coloured soluble substances

Answer 29

Paper chromatography or thin-layer chromatography

Question 30

Someone drops a glass container of copper sulfate powder on the floor and smashes it How to get the copper sulfate back?

Answer 30

- brush up the mixture of broken glass and powder, and add it to hot water - then filter the mixture to remove the glass - then obtain copper sulfate by crystallisation