H Chemistry - Unit 2 - 2e - Soaps, Detergents, and Emulsions

What are soaps?

Soaps are water soluble ionic salts of long chain fatty acids

How are soaps produced?

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

• The hydrolysis of edible oils and edible fats 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.

What can soaps be used for?

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

What do soap ions have?

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

How does the cleansing action of soap work?

The cleansing 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.

What happens when soap is used in hard water?

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

Do soapless detergents form scum with hard water?

Soapless detergents do not form scum with hard water.

What can emulsifiers be used for?

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

What does an emulsion contain?

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

How can emulsifiers for use in food be made?

Emulsifiers for use in food 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.

How do emulsifiers work?

How emulsifiers work;

• 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.