Soaps, Detergents and Emulsions

Question 1

What is formed when fats and oils are hydrolysed used an alkali?

Answer 1

Salts of the long-chain fatty acids are formed called soaps. Glycerol is also formed.

Question 2

Describe the tail of a soap molecule.

Answer 2

The tail is a long covalent hydrocarbon meaning it is non-polar, and will therefore be insoluble in water - hydrophobic. It is, however, soluble in covalent substances like grease and oil.

Question 3

What type of molecule is soap?

Answer 3

A salt

Question 4

Describe the head of a soap molecule.

Answer 4

The head is ionic or negatively charged, making it hydrophilic.

Question 5

What happens when soap is used in hard-water areas?

Answer 5

Insoluble salts (precipitate) form, known as scum. An example of this is calcium stearate.

Question 6

What ions does hard water contain?

Answer 6

Calcium and magnesium ions; dissolved metal ions.

Question 7

What cleaning product is used in hard-water areas instead of soap?

Answer 7

Detergent as it works in a similar way to soap, however, does not form insoluble salts - meaning it can lather.

Question 8

Describe the structure of detergent.

Answer 8

The molecule is similar to soap in that it has a hydrophobic hydrocarbon tail and a hydrophilic ionic head.

Question 9

How does soap work?

Answer 9

1. Soap dissolves in water, forming soap ions.
2. Tails of soap ions bury into grease leaving their heads in the water.
3. Agitation begins to separate grease from the surface causing grease globules to form in the water.
4. Micelles are prevented from recombining by negative charges on heads of soap ions in the water.

Question 10

What is an emulsion?

Answer 10

A mixture of two or more liquids that are normally immiscible, due to polarity.
Contains small droplets of one liquid dispersed in another liquid.

Question 11

What is an emulsifier?

Answer 11

They allow normally immiscible liquids to mix and stop them from separating.

Question 12

What are emulsifiers in food?

Answer 12

Mixtures of fat/oil and water.

Question 13

What are food examples of emulsions?

Answer 13

Milk and mayonnaise

Question 14

What is the natural emulsifier in milk?

Answer 14

A protein called casein.

Question 15

How can emulsifiers be made?

Answer 15

By reacting edible oils with glycerol.

Question 16

What other molecule are emulsifiers like?

Answer 16

Soap - they also have a hydrophobic part and a hydrophilic part.

Question 17

How does an emulsifier hold a mixture together?

Answer 17

The hydrophobic part dissolves in the fat/oil and the hydrophilic part dissolves in the water - holding the mixture together.

Question 18

What are E numbers?

Answer 18

Food additives/emulsifiers

Question 19

Describe these E numbers:

1. E332
2. E471

Answer 19

1. Lecithin - found naturally in eggs. It is used as an emulsifier in mayonnaise, chocolate, margarine, and chewing gum.
2. Mono- and di- glycerides - the most commonly used emulsifier in the food industry. Used in ice cream, bread, and sausages.

Question 20

What’s another effect of emulsifiers on food products?

Answer 20

They can keep products fresher for longer - and in some cases help prevent mould.

Question 21

How is soap produced?

Answer 21

By the alkaline hydrolysis of edible fats and edible oils.

Question 22

What does the hydrolysis of edible fats and edible oils produce?

Answer 22

Three fatty acid molecules and one glycerol molecule.

Question 23

From fatty acids, how is the soap then produced?

Answer 23

The molecules are neutralised by the alkali forming water-soluble ionic salts - called soaps.

Question 24

What are soaps used for?

Answer 24

To remove non-polar substances such as oil and grease.