Seperation Of Mixtures

Question 1

Filtration

Answer 1

• If the product is an insoluble solid, then filtration can be used to separate it from the liquid
• Put funnel paper in a funnel and pour mixture in

Question 2

Crystallisation

Answer 2

• Used for soluble solids
  1. Pour solution onto evaporating dish and gently heat. Some water will evaporate and conc will increase
  2. When toy see crystals start to form, then remove dish from heat and leave to cool
  3. Filter the crystals out of the solution and leave them in a warm place to dry

Question 3

How do you do paper chromatography?

Answer 3

1. Draw a line near the bottom of a sheet of filter paper and use a pencil!! (very important so that it does pint dissolve in solvent.
2. Add spots of ink to the line at regular intervals
3. Loosely roll the sheet and put it in a beaker of shallow solvent
4. The solvent depends on what is being tested, sometimes other solvents like ethanol are needed
5. Make sure the level of solvent is below the base line of the paper
6. Put a lid on the beaker to prevent evaporation
7. The solvent seeps up the paper, carrying the inks with it
8. Each dye in the inks will move at a different rate and form a spot in a different place
9. When the solvent has nearly reached the top of the paper, remove it and leave it to dry

Question 4

How does paper chromatography work?

Answer 4

• Different dyes move up the paper at different rates.
• Some will stick to the paper and some will dissolve more readily and travel more quickly
• The distance they travel depends on the solvent and paper used

Question 5

How to calculate Rf for each chemical (chromatography)?

Answer 5

Rf = distance travelled by solute / distance travelled by solvent

Question 6

Simple distillation

Answer 6

• Separates a liquid from a solution
• The solution is heated and the part with the lowest boiling point evaporates. The vapour then cools, condenses and is collected
• The problem is you can only separate things with very different boiling points

Question 7

Fractional distillation

Answer 7

• Put mixture in a flask and heat it. The liquid with the lowest boiling point will evaporate and enter the fractionating column first.
• When the temperature at the top of the fractionating column reaches the (now) gas’ boiling point, it will enter the condenser and be collected.
• Then raise the temperature and collect the next fraction