2.7 Oxidation Of Food

Question 1

Oxidation and reduction in carbon compounds

Answer 1

• oxidation is an increase in the oxygen to hydrogen ratio
• reduction is a decrease in the oxygen to hydrogen ratio

Question 2

Hot copper (II) oxide or acidified dichromate (VI) solutions

Answer 2

Hot copper (II) oxide and acidified dichromate (VI) solutions can be used to oxidise:
- primary alcohols to aldehydes and then to carboxylic acids
- secondary alcohols to ketones

During these reactions black copper(II) oxide forms a brown solid, and orange dichromate turns green.

Tertiary alcohols cannot be oxidised using these oxidising agents

Question 3

Aldehydes and ketones contain what functional group?

Answer 3

A carbonyl functional group C=O

Question 4

How to differentiate between an aldehyde and a ketone?

Answer 4

Aldehydes, but not ketones, can be oxidised to carboxylic acids.

Oxidising agents can be used if differentiate between an aldehyde and a ketone.
With an aldehyde:
- blue Fehling’s solution forms a brick red precipitate
- clear, colourless Tollen’s reagent forms a silver mirror
- orange acidified dichromate solution turns green

Question 5

What are many flavour and aroma molecules also known as

Answer 5

Aldehydes

Question 6

What causes oxidation of food?

Answer 6

Oxygen from the air causes the oxidation of food. The oxidation of edible oils gives food a rancid flavour

Question 7

Antioxidants

Answer 7

• are molecules that prevent unwanted oxidation reactions occurring
• are substances that are easily oxidised, and oxidise in place of the compounds they have been added to protect
• can be identified as the substance being oxidised in a redox equation