To test for lipids you can carry out the ethanol emulsion test. This involves adding ethanol to a sample in a test tube then shaking the mixture. Deionized water is then added.

• If no emulsion forms and the solution remains colourless then no lipids are present.
• If a cloudy white suspension appears at the top of the solution then lipids are present.

The principle surrounding this test is to do with solubilities. Due to the fact that lipids are non-polar, organic molecules they’re not soluble in water but they are in ethanol. Ethanol is also an organic substance and so is able to dissolves organic substance. However, due to its hydroxyl groups and its short C=C chain it bonds easily with water by a hydrogen bond. The hydrophobic interaction of the carbon with the water is not as strong as the hydrogen bonding.

Ethanol is able to extract the lipid but this cannot be seen until water is added at which the small droplets (micelles) which are less dense than the water rise to the top and appear cloudy due to their ability to diffract light. The micelles form because the hydrophobic part of the lipid molecule projects inwards while the hydrophilic part moves outwards to the water.