1.1.1 Separating Mixtures

Question 1

Filtration

Answer 1

Used to separate insoluble solids from a liquid via particle size difference
- solid-liquid heterogenous mixture
- E.g. sand + water

Question 2

When is vacuum filtration used?

Answer 2

When there is very little or fine solid

Question 3

Evaporation

Answer 3

Used to separate soluble solids from a liquid by heating a mixture until evaporation of the solvent using a bunsen burner to leave behind a solute.
- solid-liquid homogenous mixture
- E.g. obtaining salt from sea water

Question 4

Distillation

Answer 4

Used to separate miscible liquids

1. Mixture is heated, vaporising the volatile, lower b.p., liquid first.
2. Vapour passes through the condenser, cooling the liquid and collecting it in a separate container.
   - E.g. separating ethanol (78C bp) from water (100C bp).

Question 5

Miscible liquids

Answer 5

Liquids that form homogenous solutions when mixed together

Question 6

Solvation/Dissolution

Answer 6

Used to separate 2 solids in a heterogenous mixture based on their solubility differences.
- E.g. sugar (soluble) + sand (insoluble) + water (solvent)

1. Add solvent to dissolve only 1 solid
2. Filter insoluble solid
3. Evaporate solvent to retrieve soluble solid.

Question 7

Recrystallisation

Answer 7

Purifying an impure compound in a solvent based on solubility differences.

1. Stir + heat solution to dissolve impure compound
2. Cool solution to allow the pure compound to crystallise whilst the impure compound remains dissolved
3. Filter out pure crystals

Question 8

Paper Chromatography

Answer 8

Separates components of a mixture based on their movement through a medium.
- Stationary Phase: paper
- Mobile Phase: solvent
1. Draw a pencil line on chromatography paper and place a small sample of the mixture on it.
2. Suspend the paper in a solvent, ensuing the sample is above the solvent level.
3. Allow the solvent to travel up the paper (capillary action)
4. Solvent will dissolve the sample
5. The dissolved substances will move up the paper at different speeds depending on its solubility and affinity (how well it absorbs) to the paper.
6. Different components of the mixture will be separated into distinct spots on the paper.
- more soluble+ greater affinity: moves further up
- less soluble + lower affinity: stays closer to starting point