1.7 Describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallisation and paper chromatography

Simple Distillation
This is typically used to separate mixtures of a liquid and a soluble solid - i.e. salt and water.

• Liquid in the mixture boils in a round bottomed flask and moves up, as it is a gas
• It enters the condenser - where cool water is flowing around a tube
• It condenses again
• Drips into the conical flask / beaker / test tube / boiling tube at the end of the condenser
• In this example, the salt would be left in the round bottomed flask and the water would be in the beaker.

Fractional Distillation

This is used to separate two liquids with different boiling points - i.e. ethanol and water

• Liquid A, the one with the lowest boiling point boils first and travels up the fractionating column
• Any of liquid B that evaporates condenses and drips back down, as the beads in the fractionating column are only at the temperature of liquid A (too cold)
• Liquid A travels through the condenser, condenses again, and drips out into a container
• Liquid B remains in the round bottomed flask

Filtration

This method is typically used to separate two substances, one solid one liquid, that do not mix - i.e. sand and water

• The mixture is run through a funnel with filter paper on it into a beaker or conical flask
• The solid is trapped in the filter paper
• The liquid runs into the container

Crystallisation

This is used to create pure crystals of a solid that has been dissolved in a solvent (liquid) - i.e. salt and water

• Mixture is warmed
• Solvent evaporates
• Left to cool
• Solid forms crystals

Paper Chromatography

This is usually used to test to see the different dyes in a substance (or...well...to separate them) - i.e. using a spot of black pen

• Paper with a pencil line and a dot of substance A is put into a beaker of solvent
• Paper must not be dipped in further than the pencil line
• The solvent will travel up the paper
• The dyes will (usually) separate, travelling up the paper
• The further away from the pencil line, the more soluble the dye (due to particle size)
• If substance A does not separate, it is either pure or not soluble in the solvent.
• Sometimes, other known substances (let's say B, C and D) will be placed alongside A to see which one is present