2.5 Soaps, detergents and emulsions Flashcards
How are soaps produced?
By the alkaline hydrolysis of edible fats and edible oils.
Hydrolysis produces 3 fatty acid molecules and 1 glycerol molecule
The fatty acid molecules are neutralised by the alkali, forming water-soluble ionic salts called soaps
Use of soaps
Soaps can be used to remove non-polar substances such as oil and grease
Structure of soap
Soap ions have long non-polar tails, readily soluble in non-polar compounds ( hydrophobic), and ionic heads that are water-soluble (hydrophilic).
Action of soap
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
What is hard 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
Substances with non-polar hydrophobic tails and ionic hydrophilic heads. These remove oils and grease in the same way as soap but they do not form scum with hard water
Use of emulsifier
An emulsifier can be used to prevent non-polar and polar liquids separating into layers
What is an emulsion?
An emulsion contains small droplets of one liquid dispersed in another liquid
Emulsifiers for use in food
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 oils whilst the hydrophilic hydroxyl groups dissolve in water, for,ing a stable emulsion
