C15

Question 1

what is the equation for rust

Answer 1

iron + oxygen + water = hydrated iron (111) oxide

Question 2

what 2 things are needed for iron to rust

Answer 2

air and water

Question 3

what 5 things are used to coat iron or steel to prevent rust

Answer 3

paint (with added rust inhibitors) 
oil or grease
plastic 
less reactive metal
more reactive metal

Question 4

what does it mean to galvanise iron

Answer 4

coat it in a more reactive metal eg zinc
zinc is a strogner reducing agent than the iron so has a stronger tendency to form positive ions by giving away ions
as zinc atoms lose electrons they become oxidised so any water or oxygen reacts with the zinc rather than the iron

Question 5

what is sacrificial protection

Answer 5

for example in glavanising, the zinc is being sacrificed to protect the iron

Question 6

what 3 things can be used to sacrificially protect iron

Answer 6

zinc, magnesium, aluminium

Question 7

why are pure metals usually soft and easily shaped

Answer 7

their regular layers of positive ions in their giant lattices can slide over each other easily when forces are applied to the metal

Question 8

why are alloys harder than pure metals

Answer 8

differently sized metal ions make it harder for the layers to slip

Question 9

what is bronze an alloy of and what is it used for

Answer 9

copper and tin

statues, decorative items and ship propellors due to its toughness and resistance to corrosion

Question 10

what is brass an alloy of and what is it used for

Answer 10

copper and zinc

brass instruments, door fittings and taps as it is hard but can be hammered into sheets and intricate shapes

Question 11

why is gold alloyed with copper

Answer 11

in jewellery as pure gold wears away more easily than its copper alloy

Question 12

what is steel

Answer 12

an alloy of iron with carbon and/ or other elements

Question 13

how can properties of steel be changed

Answer 13

by controlling the amounts of carbon and other elements

Question 14

property of high carbon steel

Answer 14

strong but brittle

Question 15

property of low carbon steel

Answer 15

soft, easily shaped not as strong as high carbon steel but less likely to shatter on impact

Question 16

what is chromium nickel steel

Answer 16

stainless steel- combines hardness and strength with great resistance to corrosion and they do not rust making them good for cutlery and kitchen utensils

Question 17

what do the properties of a polymer depend on

Answer 17

the monomers used to make it

the conditions chosen to carry out the reaction

Question 18

what are the differences between the conditions used to form LD poly(ethene) and HD poly(ethene)

Answer 18

LD: high pressures and a trace of oxygen- polymer chains are randomly branched and cannot pack closely together
HD: catalyst, 50c, slightly rasied pressure- straighter poly(ethene) chains that can pack closer together than LD chains. stronger than LD

Question 19

what is a thermosoftening polymer

Answer 19

softens quite easily and then re sets when cooled. made up of individual polymer chains that are tangled together

Question 20

what is a thermosetting polymer

Answer 20

do not melt when heated as they have strong covalent bonds forming cross links between their polymer chains

Question 21

explain the forces between polymer chains in thermosoftening polymers

Answer 21

weak intermolecular forces that break when heated causing the polymer to soften. when the molecule cools the intermolecular forces bring the polymer molecules back together so the polymer hardens again

Question 22

explain the forces between polymer chains in thermosetting polymers

Answer 22

monomers make covalent bonds between polymer chains when first heated in order to shape them. the covalent bonds are strong and stop them from softening or separating. polymer will not soften but may char at a high enough temperature

Question 23

what is the most common type of glass (soda lime glass) made of

Answer 23

mainly sand but also silicone dioxide, limestone and sodium carbonate

Question 24

how is glass formed

Answer 24

the raw materials are heated to 1500c where they melt and react to form molten glass. as it cools it solidifes but the particles do not form a regular pattern

Question 25

how are ceramic objects made

Answer 25

mould the wet clay into the desired shapes and then heat in an 1000c furnace

Question 26

what is the ionic structure of ceramic

Answer 26

ionic bonding between metals and non metals that are arranged in giant structures forming layers

Question 27

why are ceramic brittle

Answer 27

a sharp blow can distort layers in their structre so that ions with like charges are adjacent and repel each other away, cracking the object

Question 28

what is the process of reinforcement in composites

Answer 28

one material surrounding and bidning together fibres or fragments of the other material

Question 29

why is the composite glass-ceramic hard and tough when both glass and ceramic are brittle

Answer 29

glass melts between the crystals in the ceramic so any cracks cannot spread throughout the whole structure

Question 30

why do fertilisers contain nitrogen

Answer 30

because plants need nitrogen to make proteins to grow

Question 31

why can plants not get nitrogen from the air

Answer 31

the gas is insouble in water and plants can only absorb a soluble form of nitrogen

Question 32

what are the conditions for making ammonia

Answer 32

450c, 200 atm and presence of an iron catalyst

Question 33

what is the equation for the haber process

Answer 33

N2(g) + 3H2(g) = (reversible) 2NH3(g)

Question 34

where does the nitrogen for the haber process come from

Answer 34

air is cooled to -200c to liquefy and then is fractionally distilled

Question 35

where does the hydrogen for the haber process come from

Answer 35

reacting methane with steam which produces hydrogen and carbon monoxide

Question 36

why is the haber process done at high pressure

Answer 36

volume of reactants is greater than volume of products so increase in pressure will shift equilibrium to the right producing more ammonia

Question 37

why is 200atm used and not a higher pressure

Answer 37

higher pressures would be expensive as they need a lot of energy and expensive reaction vessels and pipes. 200 is a compromise as it brings costs down but produces a reasonable rate of reaction

Question 38

why would a lower temperature increase ammonia yield

Answer 38

lower temperature favours the forwards, exothermic reaction as the process wants to give out heat so equilibrium shifts to the right

Question 39

why is a really low temperature not used in the haber process

Answer 39

rate of reaction would be too slow so it would take a long time for them to earn profits

Question 40

why are iron filings used as a catalyst

Answer 40

they have a large surface area and increase rate of reaction but have no effect on equilibrium as it increases forwards and backwards reaction

Question 41

what is NPK fertiliser

Answer 41

fertiliser that contains formualtions of compounds to provide all 3 of the macro nutrients : nitrogen, phosphorus and potassium

Question 42

why is phosphate rock treated before put on the soil

Answer 42

it is insoluble in water so it is treated with acids to make fertiliser salts

Question 43

what is produced when phosphate rock is treated with nitric acid

Answer 43

produces phosphoric acid and calcium nitrate. the phosphoric acid is then neutralise with ammonia to produce ammonium phosphate

Question 44

what is produced when phosphate rock is treated with sulfuric acid

Answer 44

single superphosphate is produced which is a mixture of calcium phosphate and calcium sulfate

Question 45

what is produced when phosphate rock is treated with phosphoric acid

Answer 45

triple superphosphate which is calcium phosphate