Soaps, detergents, and emulsions

Question 1

How are soaps produced?

Answer 1

When edible fats and oils hydrolyse they produce glycerol and carboxylic acids known as fatty acids. If the hydrolysis is carried out using and alkali, the fatty acids react to form a salt known as a soap.

Question 2

What are soaps used for?

Answer 2

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

Question 3

Explain, briefly, the covalent hydrocarbon chain in soap molecules.

Answer 3

The hydrocarbon tail is hydrophobic, meaning that it does not dissolve in the water.

Question 4

Explain, briefly, the carboxylate head in soap molecules.

Answer 4

The carboxylate head is hydrophilic, meaning that it does dissolve in the water.

Question 5

What is the cleansing action of soap?

Answer 5

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. The globules are now attracted to the water and easily washed away.

Question 6

What is hard water?

Answer 6

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.

Question 7

What are detergents?

Answer 7

Detergents are compounds with a soap-like structure, except it does not have a carboxylate head, meaning that it won’t form precipitates in hard-water areas.

Question 8

What is an emulsion?

Answer 8

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

Question 9

What is an emulsifier?

Answer 9

An emulsifier can be used to prevent non-polar and polar liquids from separating into layers. Soap is an example of an emulsifier because it brings together grease and water.

Question 10

How is mayonnaise an emulsion?

Answer 10

Mayonnaise is an emulsion formed by mixing olive oil and vinegar. The lecithin from the egg yolk acts as an emulsifier it contains a charged part and a long hydrocarbon tail. The vinegar is attracted to the charged part of lecithin, whilst the olive oil is attracted to the hydrocarbon part of lecithin.