Unit 2 - Nature's chemistry

Question 1

What is meant by the term “free radical”?

Answer 1

A free radical is a highly reactive species containing unpaired electrons.

Question 2

How can free radicals damage food?

Answer 2

By the removal of an electron.

Question 3

How does an antioxidant ‘cancel out’ a free radical?

Answer 3

The antioxidant molecule donates an electron to the potentially damaging free radical. A stable electron pair is formed, stabilising the free radical.

Question 4

Give an example of an antioxidant.

Answer 4

Vitamin C.

Question 5

How can esters be identified?

Answer 5

Esters can be identified by the name endings ‘yl-oate’. Esters also contain the carboxylate functional group (-COO-).

Question 6

If the parent alcohol is methanol and the carboxylic acid is hexanoic acid, what is the ester formed?

Answer 6

Methyl hexanoate.

Question 7

If the parent alcohol is butan-1-ol and the carboxylic acid is propanoic acid, what is the ester formed?

Answer 7

Butyl propanoate.

Question 8

How are esters made?

Answer 8

By a condensation reaction. Small molecules join together to form a bigger molecule by the elimination of water.

Question 9

How are esters broken?

Answer 9

By a hydrolysis reaction. Large molecules are broken down into smaller molecules by the addition of water across the ester link.

Question 10

What are the three steps to a free radical chain reaction?

Answer 10

Initiation, propagation and termination.

Question 11

How do you identify an ester?

Answer 11

With the ‘COOH’ link.

Question 12

What is a hydrolysis reaction?

Answer 12

The addition of water to break down a carbon compound.

Question 13

What is a condensation reaction?

Answer 13

A reaction in which two (or more) molecules join together to produce a single larger molecule, with water or another small molecule formed at the same time.

Question 14

What can a primary alcohol be oxidised to?

Answer 14

An aldehyde.

Question 15

If ethanol is oxidised, what is the result?

Answer 15

Ethanal (Primary alcohol is oxidised to become an aldehyde.)

Question 16

How can an aldehyde be recognised?

Answer 16

With a double bond at the start of a molecule and it having the general formula CnH2nO

Question 17

What can a secondary alcohol be oxidised to?

Answer 17

A ketone

Question 18

How can a ketone be recognised?

Answer 18

Ketones contain the carbonyl group in the middle of the carbon chain. CnH2nO is also the general formula as ketones and aldehydes are isomers.

Question 19

What is a tertiary alcohol oxidised to?

Answer 19

Tertiary alcohols show no reaction when mixed with oxidising agents and tertiary alcohols are not readily oxidised.

Question 20

What happens when an aldehyde is oxidised?

Answer 20

It becomes a carboxylic acid.

Question 21

When using acidified potassium dichromate solution as an oxidising agent, what is the colour change observed?

Answer 21

Orange to green.

Question 22

When using hot copper oxide as an oxidising agent,m what is the colour change that is observed?

Answer 22

Black to red/brown.

Question 23

When using Tollens reagant as an oxidising agent, what is the colour change observed?

Answer 23

Colourless to silver.

Question 24

When using Fehlings solution as an oxidising agent, what is the colour change observed?

Answer 24

Blue to brick red.

Question 25

What is an antioxidant?

Answer 25

An antioxidant is a substance that slows down or prevents the oxidation from occuring.

Question 26

Why are antioxidants added to some foods?

Answer 26

As they are chemicals that help to prevent the food from ‘going off’, as when food is oxidised it can become rancid, lose colour and lose nutritional value - as well as a health risk from toxic oxidation products.

Question 27

What can oxidation damage produce?

Answer 27

Free radicals.

Question 28

What is a free radical?

Answer 28

A free radical is a highly reactive species containing an unpaired electron.