C15 Using Our Resources

Question 1

What is corrosion?

Answer 1

The destruction of materials by chemical reactions with substances in the environment

Question 2

What does rusting only apply to?

Answer 2

Iron and alloys of iron (e.g. steel)

DON’T USE RUSTING WHEN TALKING ABOUT OTHER METALS, USE CORROSION

Question 3

Describe a method to test the conditions required for rusting

Answer 3

• Place iron nails in 3 different test tubes A B and C
• test tube A contains air and water
• Test tube B contains boiled water, and is sealed with oil. Boiling the water removes
  dissolved air, and the layer of oil prevents air from the test tube dissolving into the water
• Test tube C contains anhydrous calcium chloride powder, which removes all moisture
  from the air in the test tube. A rubber bung is placed onto it to prevent moist air from
  entering
• Leave for several days

Only test tube to rust is test tube A, so both water and air are required for rusting

Question 4

Why does boiling water remove dissolved air?

Answer 4

The solubility of gases tends to decrease with increasing temperature

Question 5

Name 4 ways to prevent corrosion

Answer 5

• Grease
• Paint
• Electroplating
• Sacrificial protection

Question 6

Describe, with an example, how electroplating is used to prevent corrosion

Answer 6

• A material is coated with a metal e.g. aluminium
• The surface of aluminium reacts with oxygen in the air
• This forms a thin layer of aluminium oxide, protecting the material underneath from
  further corrosion

Question 7

Describe sacrificial protection and give an example

Answer 7

• A corrosion protection method in which a less reactive metal is coated with a more
  reactive one
• Iron nails are coated in a layer of zinc - (GALVANISING)
• Layer of zinc acts as a barrier between air and water, preventing the iron from corroding
• Even if the zinc is scratches, the iron still doesn’t corrode, as zinc is more reactive than
  iron, the zinc corrodes instead of the iron

Question 8

What type of substance are alloys?

Answer 8

MIxtures

Question 9

Describe uses of alloys of copper

Answer 9

Bronze (copper + tin) - is used for STATUES as it is strong and tends not to corrode

Brass (copper + zinc) - Used for musical instruments and door handles, as it is stronger than copper and can be formed into different shapes

Question 10

Describe uses of alloys of gold

Answer 10

Gold is usually used for jewellery

Pure gold is too soft, so is alloyed with silver, copper and zinc to make it harder]

24K = 100% gold

Question 11

Describe uses of alloys of Iron

Answer 11

Steel (Iron + carbon + other metals)

High carbon steels are extremely hard, however they are brittle
- Used to make cutting tools e.g. CHISELS

Low carbon steel is softer and more easily shaped
- Used to make CAR BODIES

Stainless steel is alloyed with chromium and nickel to prevent RUSTING (resistance to corrosion) - for CUTLERY

(Iron rusts remember)

Question 12

Describe uses of alloys of aluminium

Answer 12

Airplane bodies

Aluminium alloys are low density

Question 13

Describe conditions that could change the conditions of a polymer

Answer 13

• Reaction temperature
• Reaction pressure
• Using a catalyst

Question 14

What is the difference between thermosetting and thermosoftening polymers?

Answer 14

Thermosoftening polymers melt when heated, thermosetting don’t, and they char instead

Question 15

Describe and explain the properties of thermosetting polymers

Answer 15

Polymer chains are connected by strong crosslinks. The crosslinks aren’t broken by heat and so aren’t broken by heating and therefore cannot melt

Question 16

Describe and explain the properties of thermosoftening polymers

Answer 16

Polymer chains are held together by intermolecular forces, which are weak and can be overcome easily by heat. When the forces are broken, the polymer strands are broken and the polymer melts. Thermosoftening polymers can be melted, reshaped and cooled into new shapes

Question 17

How is soda lime glass made?

Answer 17

By mixing sand, sodium carbonate and limestone, then heating in a furnace until it melts, and cooling

Soda lime glass has a low melting point which limits its uses

Question 18

How is borosilicate glass made?

Answer 18

Melting a mixture of sand and boron trioxide

Question 19

Describe how composite are made, and the general parts of a composite

Answer 19

• By mixing two different materials

Reinforcement - consists of fibres/fragments of one material
Matrix/Binder - Surrounds reinforcement

(Composite have different properties to the materials in them)

Question 20

Give examples of composites

Answer 20

Carbon fiber
Concrete
Wood