Soaps, Detergents and Emulsions SQA edition

Describe the cleaning process using a soap

During cleaning, the hydrophobic non-polar tails of soap dissolve in grease, while the negatively charged hydrophilic heads face out into the surrounding water, forming a micelle. With agitation, the grease is dislodged, and more soap ions attach. The non-polar substances (e.g. oil and grease) are trapped inside the micelle and suspended in water. The hydrophilic heads allow micelles to dissolve in water, and the negative charges on their surface cause repulsion between micelles, preventing them from clumping. This creates an emulsion, which is then washed away with the dirty water.

What happens to non-polar substances like oil and grease?

They are trapped inside micelles and suspended in water.

What part of the soap dissolves in grease?

The hydrophobic non-polar tails.

What part of the soap faces into the water?

The negatively charged hydrophilic heads.

How are soaps produced?

By alkaline hydrolysis of edible fats and oils.

What are the products of hydrolysing fats/oils?

Three fatty acid molecules and one glycerol molecule

What happens to fatty acids in the presence of alkali?

They are neutralised, forming water-soluble ionic salts called soaps.

What kind of substances can soap remove?

Non-polar substances such as oil and grease.

What are the two key parts of a soap ion?

A hydrophobic non-polar tail and a hydrophilic ionic head

What happens when soap is agitated in water with grease?

Micelles form — ball-like structures with grease trapped inside.

What keeps micelles from clumping together?

Negatively-charged heads repel each other.

What is hard water?

Water containing high levels of dissolved metal ions.

What forms when soap is used in hard water?

Scum — an insoluble precipitate.

What are soapless detergents?

Substances with non-polar hydrophobic tails and ionic hydrophilic heads that do not form scum in hard water.

What is an emulsifier?

A substance that prevents polar and non-polar liquids from separating.

What is an emulsion?

A mixture where small droplets of one liquid are dispersed in another.

How are food emulsifiers made?

By reacting edible oils with glycerol, forming molecules with 1 or 2 fatty acid chains.

In food emulsifiers, what part is hydrophilic and what is hydrophobic?

Hydrophilic hydroxyl groups dissolve in water; hydrophobic fatty acid chains dissolve in oil.

How do emulsifiers stabilise emulsions?

They dissolve in both oil and water, keeping polar and non-polar substances mixed. This creates a barrier around droplets, preventing separation.

How are soaps produced?

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

What dies hydrolysis of fats and oils produce?

Hydrolysis produces three fatty acid molecules and one glycerol molecule

How are soap molecules formed by fatty acids?

The fatty acids are neutralised by the alkali, forming water-soluble, ionic salts called soaps

What types of substances can soaps remove?

Soaps can remove non-polar substances such as oil and grease

What is the structure of a soap ion?

Soap ions have long non-polar hydrophobic tails and ionic hydrophilic heads

What happens when soap is added to oil or grease?

The hydrophobic tails dissolve in the oil or grease, while the hydrophilic heads remain in the water

What causes the formation of ball-like structures in soapy water?

Agitation causes ball-like structures to form where the hydrophilic heads face outward and repel each other

What is the result of these negatively-charged ball-like structures?

They keep oil or grease suspended in the water, allowing it to be rinsed away.

What is hard water?

Water that contains high levels of dissolved metal ions

What happens when soap is used in hard water?

Scum, an insoluble precipitate, is formed.

What are soapless detergents?

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

How do soapless detergents work?

They remove oil and grease in the same way as soap.

Why are soapless detergents preferred in hard water?

They do not form scum with hard water.

How can food emulsifiers be made?

By reacting edible oils with glycerol.

What is the structure of emulsifier molecules used in food?

Only one or two fatty acid groups are linked to each glycerol backbone.