Chem-Topic 2-seperating substances

Topic 2 - Separating Substances - Summary Sheets

Filtration

Filtration is used to separate insoluble solids from a solution. It will not separate a herr

solute from a solution as the solute is soluble and has dissolved into the solution. I must be an insoluble solid and a solution.

A funnel with filter paper in is positioned above a conical flask. The insoluble solid i trapped in the filter paper, this is called the residue.

The solution can fit through the small holes in the filter paper and drip into the conical flask. This is called the filtrate.

There are two methods of filtration: gravity filtration and vacuum filtration. Gravity filtration used gravity to pull the filtrate through the filter paper. An example of vacuum filtration used a Buchner funnel where the funnel is attached to a pump an reduced pressure pulls the filtrate through.

large enough particles of solid cannot fit through tiny holes in filter paper, so remain here

Crystallisation

Crystallisation is used to separate a solution. It will separate the soluble solid (the solute) from the solvent.

An evaporating basin is put onto of a Bunsen burner (using a tripod and gauze.) The evaporating basin is gently heated till the volume of the solution goes down by half. The solution is then left on the side to further crystallise.

The solvent within the solution evaporates into the atmosphere and the solute is left in the evaporating dish. The diamond shaped crystals will be left in the dish.

Distillation

Distillation separates mixtures of liquids where each liquid has a different boiling point (turns into a gas at different temperatures.)

The mixture is heated in a round bottom flask. When one of the liquids reaches its boiling point (checked by the thermometer above,) it will evaporate into a gas, rise and travel along to the Liebig condenser.

The condenser has an outer layer surrounding the inner tube which has a constant flow of cold water in (constant flow is made due to the water going in at the bottom not the top.) The inner tube is now cold so the gases will condense into a liquid and drip out of the condenser at the end to be collected.

This has separated one liquid from the other which is left in the starting flask.

Chromatography

Chromatography another separation technique used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks or plant pigments.

A solvent that all the substances can dissolve in is used. For example, water is often used for ink and ethanol is used for the pigments in grass as these pigments are not soluble in water.

The substances dissolve in the solvent, the solvent moves through some special paper and

'drops' certain substances/colours at different points.

The usual pattern is yellow and lighter colours are most soluble so travel the furthest on the paper and dark colours are least soluble so don't travel as far.