Using materials

Question 1

What is corrosion

Answer 1

Corrosion is the destruction of materials by chemical reactions with substances in the environment

Question 2

word equation for iron rusting

Answer 2

iron + oxygen + water -> hydrated iron oxide

Question 3

How to prevent corrosion

Answer 3

• applying a coating that acts as a physical barrier so the material won’t be in contact with other substances e.g.: greasing, electroplating or painting
  These methods stop air or water coming into contact with the metal
• Sacrificial protection: some coatings are reactive and may contain a more reactive metal. If two metals are in contact the more reactive metal will corrode instead of the less reactive one

Zinc is used to galvanise iron and when scratched provides sacrificial protection as zinc is more reactive than iron.
Magnesium blocks can be attached to steel ships and provide sacrificial protection. Magnesium blocks can be replaced from time to time, which is cheaper than replacing steel on ships

Question 4

Why are alloys used

Answer 4

Pure copper, iron, gold and aluminium are too soft for many uses and so are mixed with other metals to make them harder for everyday use

Question 5

what is an alloy

Answer 5

a mixture of different metals

Question 6

examples of alloys

Answer 6

Bronze - copper ant tin for statues and decorative objects

Steel - iron that contain specific amounts of carbon and other metals. High carbon steel is strong but brittle. Low carbon steel is softer and more easily shaped

Brass - copper and zing, used to make water taps and glass door fittings

Question 7

Thermosetting polymers

Answer 7

Do not melt when heated because of the strong covalent bonds between chains

HDPE - high density polyethene

Question 8

Thermosoftening polymers

Answer 8

Soften easily when heated and can be remoulded, keeping the new shape on cooling. Polymer molecules are attracted to eachother by weak intermolecular forces of attraction
LDPE

Question 9

Soda lime glass

Answer 9

heating mixture of sand, sodium carbonate and limestone

Question 10

Borosilicate glass

Answer 10

made from sand and boron trioxide, melts at higher temperatures than soda lime glass

Question 11

Difference in properties between HDPE and LDPE

Answer 11

HDPE: Chains pack closely together, making it stronger, more rigid and higher in density
LDPE: Branches prevent chains from packing closely, making it softer, flexible and low in density

Question 12

Differences in use between HDPE and LDPE

Answer 12

HDPE: buckets, pipes, plug sockets
LDPE: plastic bags, bubble wrap

Question 13

What is a composite material

Answer 13

A material that consists of two or more materials with different properties. They are combined to make a material with improved properties

Question 14

what two components do composite materials have

Answer 14

• the reinforcement
• the matrix, which binds the reinforcement togther

Question 15

advantages of Reinforced concrete with steel

Answer 15

Concrete has high compressive strength
Steel has high tensile strength
The material can withstand high tension and compression, without snapping or breaking

Question 16

advantages of reinforcing polymer resin with glass fibre or carbon fibre

Answer 16

Carbon fibre is stiff, lightweight, very strong, high tensile strength but also low density

Question 17

borosilicate glass vs soda lime

Answer 17

Soda lime: hard, transparent, relatively low melting point - bottles and windows
Borosilicate: higher melting point, resistant to thermal expansion, transparent, chemically stable making it suitable for laboratory use, glassware and kitchen ware

Question 18

Using clay for pottery and bricks

Answer 18

• shaping wet clay and heating it in a furnace to harden it
  properties: water proof, hard, unreactive, resistant to heat. Used in crockery, pottery and bricks

Question 19

What is a ceramic

Answer 19

An inorganic, non-metal solid made from metal/non-metal compounds. Doesn’t contain carbon

Question 20

what is the Haber process used for

Answer 20

to manufacture ammonia, used for nitrogen based fertilisers

Question 21

How does the Haber process work

Answer 21

reaction of nitrogen gas and hydrogen gas - ammonia is produced in a gaseous form

Question 22

how is hydrogen and nitrogen obtained for the haber process

Answer 22

• nitrogen: atmosphere/air
• hydrogen: reacting methane with steam: fossil fuels needed for methane, infinite resource. making steam requires a lot of energy

Question 23

Why is the reaction being reversible a problem

Answer 23

Some ammonia breaks back down into H2 and N2. The yield is never 100%

Question 24

Conditions needed for the haber process

Answer 24

450 degrees C
200 atmospheres
iron catalyst - has no affect on the equilibrium, just speeds up the forwards and backwards reaction at the same rate.

Question 25

why 450 degrees is used

Answer 25

A higher temperature will shift the position of the equilibrium to the left because that is the endothermic side. An increase in temperature would decrease the yield. However a high temperature would give a higher rate of reaction because of more frequent collisions. But it would also be more expensive to maintain. 450 degrees C is used as a compromise to all these factors

Question 26

why 200 atmospheres is used

Answer 26

A higher pressure would cause the position of the equilibrium to move to the right and increase the yield, and also increase the rate of reaction due to more frequent collisions. However higher pressures mean high energy and equipment costs. The chosen pressure is a compromise

Question 27

Why is an iron catalyst used

Answer 27

Presence of a catalyst will not affect the position of the equilibrium, but it will reduce activation energy, so it increases the rate of reaction