2.7 Oxidation of Food

Question 1

What are the 3 types of oxidation

Answer 1

• Loss of electrons
• Gain of oxygen
• Loss of hydrogen

Question 2

What does oxidation always result in

Answer 2

An increase in the oxygen to hydrogen ratio

Question 3

When oxidation is occurring what is also occurring

Answer 3

Reduction

Question 4

Name 3 oxidising agents

Answer 4

Acidified sodium dichromate
Potassium permanganate
Copper (II) oxide

Question 5

What are the only types of alcohols that can oxidise

Answer 5

Primary and Secondary

Question 6

What happens when potassium permanganate is reduced

Answer 6

Purple permanganate ion turns to colourless Mn2+ ions

Question 7

What happens when sodium dichromate is reduced

Answer 7

Orange dichromate ion turns to green Cr3+ ions

Question 8

What happens when hot copper oxide is reduced

Answer 8

Black oxide turns to reddish copper metal

Question 9

What happens when primary alcohols are oxidised

Answer 9

It forms an aldehyde

Question 10

What happens when you oxidise a secondary alcohol

Answer 10

It forms a ketone

Question 11

What is the functional group for aldehydes and ketones

Answer 11

Carbonyl group

Question 12

Where is the carbonyl group in an aldehyde

Answer 12

At the end of the carbon chain

Question 13

Where is the carbonyl group in a ketone

Answer 13

It is attached` to other carbon atoms

Question 14

What is the general formula for aldehydes and ketones

Answer 14

CnH2nO

Question 15

What compounds can Acidified potassium dichromate oxidise

Answer 15

Primary and Secondary alcohols

Question 16

What is the colour change for acidified potassium dichromate

Answer 16

Orange > blue/green

Question 17

What compounds will Fehling’s solution oxidise

Answer 17

Only aldehydes

Question 18

What is the colour change for Fehling’s solution

Answer 18

Blue > orange/red

Question 19

What compounds will Tollens reagent oxidise

Answer 19

Only aldehydes

Question 20

What is the colour change for Tollens reagent

Answer 20

Colourless > silver mirror

Question 21

What is a useful way of determining weather oxidation has occurred

Answer 21

Calculating the oxygen to hydrogen ratio (It decreases when oxidation has occurred)

Question 22

When cooking vegetables how is flavour released

Answer 22

Flavour is usually trapped inside the cell wall, cooking damages the cell wall letting it out

Question 23

Give two examples of aldehydes of ketones used in food

Answer 23

Limonene and Vanillin

Question 24

What can happen when vitamin C is cooked in water

Answer 24

Since vitamin C is polar, it may dissolve in the water

Question 25

Why should something be cooked in a solvent that is the opposite of its polarity

Answer 25

So the flavour molecules do not dissolve

Question 26

What happens when proteins are heated during cooking

Answer 26

They denature, allowing them to change shape

Question 27

Give an example of a protein that denatures when cooking meat

Answer 27

Collagen

Question 28

When can oxidation of food occur

Answer 28

When food is exposed to oxygen in the air

Question 29

What kind of foods are at the greatest risk of oxidisation

Answer 29

Foods containing fats or oils

Question 30

How can oxidation of food be avoided

Answer 30

Packing it with nitrogen, an inert gas that will not react with the food

Question 31

Name effects of oxidisation on food

Answer 31

Loss of colour Deterioration of flavour Loss of nutritional value

Question 32

What is an antioxidant

Answer 32

A substance that slows down or prevents the oxidation of another chemical

Question 33

What type of agent are antioxidant molecules

Answer 33

Reducing agents

Question 34

What can oxidation reactions produce

Answer 34

Free radicals

Question 35

How can free radicals damage food

Answer 35

By removing electrons

Question 36

How does an antioxidant cancel a free radical

Answer 36

The antioxidant donates an electron and stabilises the free radical as a stable electron pair is formed. The antioxidant itself is then oxidised

Question 37

Give an example of an antioxidant

Answer 37

Vitamin C