2.5 Miscellaneous Separation Methods and other apparatus uses

Remember, in the physical processes of using a separating funnel, magnetic separation, centrifuge separation, no chemical reaction changes are involved, so no new substances are made.

How can we separate two liquids that do not mix?

Distillation is used to separate miscible liquids that dissolve in each other and have different boiling points

 If two liquids do NOT mix, they form two separate layers and are known as immiscible liquids (e.g. oil/water). This is illustrated in the diagram on the left, where the lower grey liquid will be more dense than the upper layer of the yellow liquid and shows how you can separate these two liquids using a separating funnel. (particle picture on gas-liquid-solid page)

1. The mixture is put in the separating funnel with the stopper on and the tap closed and the layers left to settle out. The more dense liquid will always from the lower layer.

2. The stopper is removed, and the tap is opened so that you can carefully run the more dense lower grey layer off first into a beaker.

3. This leaves behind the upper yellow layer liquid, so separating the two immiscible liquids. You can separate oil and water in this way or an organic solvent from an aqueous layer.

AND

in these separation procedures there always loss of product so at a higher level (GCSE/IGCSE/A Level) you need to know about

 % reaction yield & reasons for loss of product

atom economy  *  % purity of a product

I'm afraid there is a bit more to it than just a bit of glass apparatus !!!

 MAGNET

How can we separate pieces of iron from a mixture of solids?

e.g. in scrap iron/steel metal from non-magnetic metals like copper or aluminium.

You can retrieve scrap iron or steel form domestic waste.

A magnet can be used to separate iron filings from a mixture with sulfur powder.

It is used in recycling to recover iron and steel from domestic waster i.e. the 'rubbish' is on a conveyer belt that passes a powerful magnet which pluck's out magnetic materials.

Methods of collecting gases are on a separate web page. Includes the preparation of ammonia, carbon dioxide, sulphur dioxide, hydrogen and a cracking experiment.

Solvent Extraction

In its simplest form these techniques involve using a liquid to dissolve a solid to separate it from a mixture.

The extraction of pure salt from a sand-salt mixture is a simple example of the technique.

Solvent extraction may dissolving out a desired product where the mixture involves two immiscible liquids or solution.

For more complex examples see the advanced level chemistry page.

Advanced A level chemistry - solute distribution between two immiscible liquids, partition coefficient , calculations and uses

How can we separate fine particles of an insoluble solid from a liquid?

(other than filtration and not waiting a long time for sedimentation!)

Centrifuges are devices or apparatus that can be used to separate insoluble materials (usually a solid) from a liquid, where normal filtration does not work well e.g. a suspension of very fine (tiny) solid particles.

The centrifuge consists of carriage or glass tube holder, mounted on an electrically motor driven vertical axle.

The carriage holds the balanced glass tubes of equal amounts of the solid-liquid mixture in each tube, all tubes initially in a horizontal position before the motor is switched on. 

The tube carriage is rotated at high speed safely in a fully enclosed container. Unbalanced tubes can break with the extra vibration and this situation has a 'knock on' effect, quite literally, as other tubes are likely to shatter with the erratic high speed unbalanced motion. High velocity glass fragments are not good for you!

On rapid rotation of the carriage the tubes whirl round horizontally and the centrifugal force causes the more dense insoluble material particles to move outwards, separating from the liquid.

When rotation ceases the solid particles end up at the 'bottom' of the glass tubes with the liquid above.

After the centrifuging operation the liquid can be decanted off and the solid is left at the bottom of the glass tube.

You might be interested in the solid, liquid or both products depending on the context.

Centrifuges come in all sizes and centrifuge technology has many applications in the separation of mixtures and the purification of materials.

If [ ] represents the glass tubes, the horizontal rotation situation is shown below ..

[solid/liquid] <== axle | carriage ==> [liquid\solid]

Uses-applications: In biology cells can be separated from fluids. A waste 'sludge' can be treated e.g. removing toxic solids from contaminated water from an industrial process. Milk can be separated from whey. Edible oils, wines and spirits can be cleaned or 'clarified' of solid impurities. Expensive oils and other fluids used as lubricants in machining metal parts in industry become contaminated with tiny metal fragments. The larger pieces of metal are easily removed by filtration or sedimentation (allowing to settle out) but the very fine metal particles can only be removed by using a centrifuge. This is likely to be a cheaper option than buying more machine fluid AND reducing pollution since the fluid is recycled leaving less waste to dispose of.

TOP OF PAGE and sub-index