Soaps are produced by the alkaline hydrolysis of edible fats and edible oils.

• Hydrolysis produces three fatty acid molecules and one glycerol molecule.
• The fatty acid molecules are neutralised by the alkali, forming water-soluble, ionic salts called soaps.

Soaps can be used to remove non-polar substances such as oil and grease.

Soap ions have long non-polar tails, readily soluble in non-polar compounds (hydrophobic), and ionic heads that are water-soluble (hydrophilic).

The hydrophobic tails dissolve in the oil or grease.

The negatively-charged hydrophilic heads remain in the surrounding water.

Agitation causes ball-like structures to form.

The negatively-charged ball-like structures repel each other and the oil or grease is kept suspended in the water.

Hard water is a term used to describe water containing high levels of dissolved metal ions.

When soap is used in hard water, scum, an insoluble precipitate, is formed.

Soapless detergents are substances with non-polar hydrophobic tails and ionic hydrophilic heads.

Soapless detergents remove oil and grease in the same way as soap.

Soapless detergents do not form scum with hard water.

An emulsion contains small droplets of one liquid dispersed in another liquid.

An emulsifier can be used to prevent non-polar and polar liquids separating into layers.

Emulsifiers for use in food can be made by reacting edible oils with glycerol.

In the molecules formed, only one or two fatty acid groups are linked to each glycerol backbone.

The hydroxyl groups present in the emulsifier are hydrophilic whilst the fatty acid chains are hydrophobic.

The hydrophobic fatty acid chains dissolve in oil whilst the hydrophilic hydroxyl groups dissolve in water, forming a stable emulsion.