Oxidation of Food

Question 1

Name six chemicals found in food.

Answer 1

Aldehydes
Ketones
Alcohols
Carboxylic acids
Fats
Oils

Question 2

What can happen to chemicals in food?

Answer 2

They can be oxidised by oxygen in the air, which spoils the food.

Question 3

Between the alcohol and alkane with the same number of carbons, which has the higher boiling point?

Answer 3

Alcohol

Question 4

What happens to the boiling points of alcohol as the number of carbons increase?

Answer 4

It increases.

Question 5

Explain the difference in the bonding of alcohols compared to alkanes.

Answer 5

Alcohol molecules have a polar -O-H group, resulting in hydrogen bonding. The hydrogen bonds are much stronger compared to the London dispersion forces between alkane molecules. This means alcohols require more energy to separate, giving higher boiling points than alkanes.

Question 6

How can alcohols be classed?

Answer 6

Primary, secondary and tertiary.

Question 7

How many carbons are attached to the carboxyl group in a primary, secondary, and tertiary alcohol?

Answer 7

1, 2, 3.

Question 8

What is a diol?

Answer 8

An alcohol with two hydroxyl groups.

Question 9

What is an alcohol with three hydroxyl groups called?

Answer 9

Triol

Question 10

Name a common triol.

Answer 10

Glycerol (propane-1,2,3-triol) - the alcohol part of fats and oils.

Question 11

Why do diols and triols have high boiling points?

Answer 11

Due to strong hydrogen bonding between molecules.

Question 12

What does it mean if a product has a higher oxygen : hydrogen ratio than the reactant?

Answer 12

Oxidation has taken place.

Question 13

Can tertiary alcohols be oxidised?

Answer 13

No

Question 14

What are primary alcohols oxidised to?

Answer 14

Aldehydes, and then oxidised again into carboxylic acids.

Question 15

What can secondary alcohols be oxidised to?

Answer 15

Ketones

Question 16

What can a carboxylic acid be reduced to?

Answer 16

The corresponding aldehyde and alcohol. The oxygen:hydrogen ratio decreases from acid to alcohol, indicating a reduction.

Question 17

What do carboxylic acids neutralise?

Answer 17

Bases, to form salts.

Question 18

What can salts of a carboxylic group be used as?

Answer 18

Preservatives in food and prevent the growth of mould.

Question 19

What is particularly susceptible to oxidation?

Answer 19

Oils

Question 20

What happens when food spoils, due to oxidisation?

Answer 20

Products are formed, some of which have an unpleasant smell and taste. These products can be oxidised further, at the double bonds, releasing volatile aldehydes which also smell.

Question 21

How is an oil of fat described when oxidised/spoiled?

Answer 21

Rancid

Question 22

What is used to reduce the oxidation of chemicals in food?

Answer 22

Antioxidants - they extend the shelf life of food.

Question 23

What does an antioxidant do?

Answer 23

Some react with the oxygen, while others prevent the formation of soapy tasting peroxides.

Question 24

Name a common antioxidant used in food.

Answer 24

Ascorbic acid (vitamin C)

Question 25

What is an isomer?

Answer 25

Molecules that have the same molecular formula but a different arrangement of atoms.

Question 26

What is chain isomerism?

Answer 26

The atoms are arranged in a completely different order resulting in branches.

Question 27

What is position isomerism?

Answer 27

The basic carbon skeleton remains unchanged but functional groups can be moved around.

Question 28

What similar chemical compounds exhibit isomerism?

Answer 28

Esters, aldehydes, ketones, alcohols, and carboxylic acids.

Question 29

Which molecules can’t have positional isomers, and why?

Answer 29

Aldehydes and carboxylic acids, because the functional group must always be on the end carbon.

Question 30

What is functional group isomerism?

Answer 30

Molecules that contain different functional groups.