Oxidation of food

Question 1

What are oxidation and reduction?

Answer 1

1. Oxidation is an increase in the O:H ratio.
2. Reduction is a decrease in the O:H ratio.

Question 2

Oxidation of a primary alcohol

Answer 2

1. Primary alcohol
2. Aldehyde
3. Carboxylic acid

Question 3

Oxidation of a secondary alcohol

Answer 3

1. Secondary alcohol
2. Ketone

Question 4

What are the oxidising agents and their colour changes?

Answer 4

1. Hot copper (II) oxide – black to brown solid
2. Acidified dichromate (VI) solution – orange to green
3. Fehling’s solution – blue to brick red
4. Tollens’ reagent – clear to silver mirror

Question 5

Why can’t tertiary alcohols be oxidised?

Answer 5

Due to the position of the hydroxyl group – because there is a branch, a =O cannot be formed.

Question 6

Use of aldehydes

Answer 6

Aldehydes often have distinct flavours and aromas so can be used in food products or essential oils.

Question 7

What happens when edible oils react with oxygen in the air?

Answer 7

They become rancid.

Question 8

What are antioxidants?

Answer 8

Antioxidants are molecules that prevent unwanted oxidation reactions to occur by being oxidised in their place (they are reducing agents).