using a separating funnel Doc Brown's Chemistry KS4 science GCSE/IGCSE/O Level Chemistry Revision Notes



PART 2.5 Methods of separating mixtures are described e.g. separating funnel, solvent extraction, centrifuge, centrifuging, decanting-decantation, separating substances with a magnet

Part 1 Definitions in Chemistry, Elements, Compounds & Mixture pictures & Physical & Chemical Changes

Part 2 Methods of Separating Mixtures of substances

Part 3 How to write equations, work out formula and name compounds

Alphabetical list of KEYWORDS for Parts 1-3: atom  *  balancing equations (work your way down the section carefully)  *  centrifuges/centrifuging  *  chemical reaction/change  *  chromatography (paper/thin layer)  *  compound  *  covalencycrystallisation  *  decanting/decantation  * displayed formula  *  distillation (simple or fractional)  *  element  *  equations  *  evaporation  *  filtration  *  formula  * gas chromatography  *  impure/pure  *  insoluble  *  ionic equations  *  ionic valence  *  iron-sulphur separation and heating experiment  *  magnet  *  mixture  *  molecule  *  naming compounds and ions  *  particle pictures of elements/compounds/mixtures  *  physical change  *  precipitation  *  products  *  pure substance  *  purification  *  reactants  *  sand/salt separation  *  separating funnel  *  separating mixtures  *  soluble/solution/solvent/solute  *  solvent extraction  *  symbols (for elements, formula, in equations)  *   state symbols  *  EleCmdMix3.htm  * working out formulae  *


 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.

Separating funnel

using a separating funnel

How can we separate two liquids that do not mix?

Distillation, described above is used to separate miscible liquids that dissolve in each other. 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.


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 !!!


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.

Use of U tube to collect things in e.g. condensing out water in a combustion investigation Testing for water and carbon dioxide, the products of burning/combustion of a candle/hydrocarbon (c) doc b
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 level chemistry - solute distribution between two immiscible liquids, partition coefficient , calculations and uses

Centrifuges and centrifuging

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

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.


See other web page for:

(c) doc b KS3 Science GCSE/IGCSE Chemistry States of Matter - kinetic particle theory of Gases, Liquids and Solids revision notes

(c) doc b KS3-GCSE/IGCSE Types of Chemical Reaction revision notes

(c) doc b GCSE/IGCSE Chemical Bonding revision notes (ionic, covalent, metallic etc.)


GCSE balancing and completing equation exercises:

(1) multiple choice * (2) number/word multi-fill

GCSE 'name and formula' of a compound quizzes

(1) pick the name given the formula * (2) pick the formula given the chemical name

GCSE/IGCSE formula quiz given the name, type in the formula

GCSE/IGCSE name quiz given the formula, type in the name

KS3 Science-GCSE/IGCSE Elements, Compounds & Mixtures m/c QUIZ

KS3 Science-GCSE/IGCSE element name/symbol quiz

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