Unit 2-Skin Care

Question 1

What name is given to the high energy radiation from the sun which can damage skin?

Answer 1

Ultraviolet radiation (UV)

Question 2

What effect does UV have on the human body?

Answer 2

Causes sunburn and contributes to ageing of the skin.

Question 3

What effect does exposure to UV light have on molecules?

Answer 3

Molecules gain enough energy for bonds to be broken.

Question 4

How do sun-block products work?

Answer 4

Sun-block products prevent UV light reaching the skin.

Question 5

What can be formed when bonds are broken by UV light?

Answer 5

Free radicals

Question 6

What is a free radical?

Answer 6

Free radicals are highly reactive atoms that have one unpaired electron.

Question 7

Why are free radicals highly reactive?

Answer 7

They are unstable as there is a tendency for unpaired electrons to pair up and so the free radicals react very quickly.

Question 8

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

Answer 8

1. Initiation.
2. Propagation
3. Termination

Question 9

Describe the initiation stage in a free radical chain reaction.

Answer 9

UV light is absorbed and homolytic fission (the two shared electrons separate equally, one going to each atom) occurs, forming free radicals.

Question 10

Describe the propagation stage in a free radical chain reaction.

Answer 10

The original free radicals react to become stable and form new reactive free radicals.

Question 11

Describe the termination stage in a free radical chain reaction.

Answer 11

Two free radicals combine and cancel each other out to form stable oxidation products.

Question 12

Are the following reactions initiation, propagation or termination steps?

A. Cl. + Cl. –> Cl₂

B. Cl. + CH₄ –> CH₃. + HCl

C. CH₃. + Cl. –> CH₃Cl

D. Cl_{2<span> </span>}–> Cl. + Cl.

Answer 12

A is a termination step

B is a propagation step

C is a termination step

D is an initiation step

Question 13

What is meant by a free radical scavenger?

Answer 13

Free radical scavengers are molecules which can react with free radicals to form stable molecules and prevent chain reactions.

Question 14

Free radical scavengers can be added to food products.

Name another product which has added free radical scavengers.

Answer 14

Sun blocks-to minimise damage caused by free radicals

Cosmetics-as above

Plastics-many plastics contain groups that are vulnerable to free radical oxidation so free radical scavengers are added to prolong their use.