C15 Flashcards
corrosion of iron
rusting
rust
hydrated iron (III) oxide
rusting equation
iron + oxygen + water –> hydrated iron (III) oxide.
how to prevent corrosion
coat the metal with paint, grease or plastic. Iron not in contact with the air and water needed for rusting
sacrificial protection
Coating that use a more reactive metal to provide protection. Even if the coating is scratched, the iron doesn’t rust.
Galvanised iron
Iron covered in a layer of zinc.
zinc is more reactive than iron because it has a stronger tendency to form positive ions by giving away electrons.
Any water or oxygen reacts with the zinc not the iron.
Sacrificial protection as the zinc is sacrificed to save the iron.
Why doesn’t aluminium metal corrode?
A protective oxide layer forms on the aluminium metal. This protects the aluminium beneath it from further corrosion.
Bronze
Alloy of copper and tin.
Used to make statues and ships’ propellers, as bronze is
tough and resistant to corrosion.
Brass
Alloy of copper and zinc
Brass is much harder than copper
and is used to make musical instruments, door fittings and taps.
aluminium
Has a low density for a metal
Lightweight but strong
Aluminium alloys are used to build aircraft.
Gold
Can be made harder by adding other elements - gold usually alloyed with silver, copper and zinc in jewellery.
Proportion of gold often expressed in carats- 24-carat gold is pure gold (100%), 18-carat gold is 75% gold.
alloys of iron
alloys of iron are called steels
Pure iron too soft for many uses.
Properties of steel can be changed for different uses by carefully controlling the amounts of carbon and other elements.
simplest steels
carbon steels
high-carbon steel is very strong but brittle. Used in cutting tools.
low-carbon steel is softer and more easily shaped, can be used to make car bodies.
stainless steels
Chromium-nickel steels
Hard, strong and resistant to corrosion.
Used in cutlery.
types of polymer
thermosoftening polymers and thermosetting polymers
what do the properties of a polymer depend on
the monomers used to make it
the conditions used to carry out the reaction
types of poly(ethene)
high density(HD) poly(ethene) low density(LD) poly(ethene)
high density poly(ethene)
Made from ethene
using a catalyst
at 50 degrees Celsius,
and a slightly raised pressure.
low density poly(ethene)
Made from ethene using a very high pressure and a trace of oxygen
Differences between high density poly(ethene) and low density poly(ethene)
HD poly(ethene) has a higher softening temperature and is stronger than LD poly(ethene)
thermosoftening polymer
eg. poly(ethene)
Made of individual polymer chains tangled together
Forces between polymer chains are weak.
When heated, the weak intermolecular forces are broken and the polymer becomes soft. When it cools down, the intermolecular forces bring the polymer molecules back together so the polymer hardens again.
This means it can be heated to mould it into shape and it can be remoulded by heating again.
Thermosetting polymers
Don’t melt or soften when heated.
Set hard when they are first moulded because strong covalent bonds form cross-links between their polymer chains. These strong covalent bonds hold the polymer chains in position.
most common form of glass
soda-lime glass
Raw materials: sand, limestone and sodium carbonate. Heated together to produce soda-lime glass.
Borosilicate glass
Made from sand and boron trioxide
Used for ovenware as it melts at higher temperatures than soda-lime glass.
Examples of ceramic objects made from clay
Bricks, pottery, crockery, sinks and toilets
Clay ceramics properties
Hard but brittle materials
Electrical insulators
Resistant to chemical attacks
How are ceramics made?
moulding wet clay into shapes
and then heating them in a furnace
composites
reinforcement
most composites are made of 2 materials
makes a product with improved properties for a particular use
contain a matrix (binder) of one material surrounding & binding together fibres or fragments of the other material - a process called reinforcement.
Glass-ceramic
Glass & ceramics- both brittle. When combined and heated together, they form a composite glass-ceramic, which is hard and very tough.
common composites and their properties
Glass & ceramics- both brittle. When combined and heated together, they form a composite glass-ceramic, which is hard and very tough.
Fibreglass- composite of glass with polymers as the matrix/binder material. Tough, flexible waterproof material with a low density
concrete- very hard and strong composite that is very strong in compression. Can be made more resistant to bending forces by setting it around a matrix of steel rods, forming ‘reinforced concrete’.
fibreglass
composite of glass with polymers as the binding material.
Forms a tough, flexible, waterproof material with a low density
concrete
very hard, strong composite that is very strong in compression. It can be made more resistant to bending forces by by setting it around a matrix of steel rods, forming ‘reinforced concrete’
common composites
glass-ceramic
fibreglass
concrete
the Haber process
used to manufacture ammonia
the Haber process
used to manufacture ammonia
ammonia use
to make fertilisers and other chemicals
Raw materials in the Haber process
nitrogen from the air
hydrogen obtained from natural gas
Haber process conditions
pressure of 200 atmospheres and temperature of 450 degrees Celsius
Iron catalyst used
yield of ammonia in the Haber process
about 15% because some of the ammonia produced breaks down into nitrogen and hydrogen as the reaction is reversible
describe the Haber process
purified nitrogen and hydrogen pumped into reaction chamber, passed over an iron catalyst at 450 oc and 200 atmospheres. The gases that come out of the reactor are cooled so the ammonia condenses. The liquid ammonia is separated from the unreacted gases. The unreacted gases are recycled so that they aren’t wasted.
What is done in the Haber process to conserve raw materials?
The unreacted gases are recycled so they aren’t wasted
Equation of the Haber process
N2(g) + 3H2 (g) ——> 2NH3 (g)
Effect of increasing pressure in the Haber process
Products have fewer molecules of gas than the products
an increase in pressure will shift the position of equilibrium to the right, forming more product(more ammonia)
Higher pressure = higher yield of ammonia
Why is a pressure of 200 atmospheres used in the Haber process?
Although 200 atmospheres gives a lower yield than higher pressures, it reduces the cost and helps to produce a reasonable rate of reaction between the gases.
Effect of increasing temperature on the yield in the Haber process
Forward reaction in the Haber process in exothermic, so a higher temperature actually decreases the yield of ammonia as the backwards endothermic reaction is favoured.
Why is a temperature of 450 degrees Celsius used in the Haber process?
Higher temperature decreases yield, but increases the rate of reaction so a reasonable yield is produced in a short time.
Why is a catalyst used in the Haber process?
Iron catalyst used.
Speeds up the rate of the forwards AND BACKWARDS reactions by the same amount.
Therefore, it doesn’t affect the yield of ammonia but it means that ammonia is produced faster which is an important economic consideration in industry.
compounds of ammonia
Most of the ammonia made in the Haber process is changed into compounds of ammonia.
These compounds are often used as fertilisers
eg. ammonium nitrate, ammonium sulfate, ammonium phosphate.
nitric acid
Some of the ammonia made in the Haber process is converted in another process into nitric acid.
Nitric acid is reacted with ammonia solution to make ammonium nitrate fertiliser
ammonia + nitric acid—> ammonium nitrate
making fertiliser salts
Can be made by reacting ammonia solution (an alkali) with different acids
ammonia solution + nitric acid –> ammonium nitrate
ammonia solution + sulfuric acid –> ammonium sulfate
ammonia solution + phosphoric acid —> ammonium phosphate
These salts are formed in a neutralisation reaction. You can make these salts by titration, eg. can make ammonium sulfate in the lab by the titration of dilute sulfuric acid against ammonia solution.
ammonium nitrate
ammonia solution + nitric acid
ammonium sulfate
ammonia solution + sulfuric acid
ammonium phosphate
ammonia solution + phosphoric acid
what nutrients do crops need for healthy growth
nitrogen, N
phosphorus, P
potassium, K
NPK fertilisers
contain formulations of compounds to provide all 3 elements (nitrogen, phosphorus and potassium) for healthy plant growth in appropriate proportions
Ammonia process to make fertilisers
ammonia produced in the Haber process.
Ammonia reacted with acids to make fertilisers, eg. ammonium nitrate(nitric acid)
source of phosphorus in fertilisers
deposits of phosphate-containing rock, which is mined from the ground. The phosphate rock is insoluble in water, so it is treated with acids to make soluble fertiliser salts.
phosphate rock and nitric acid
Phosphate rock is treated with nitric acid to produce phosphoric acid and calcium nitrate. Phosphoric acid is then neutralised with ammonia solution to produce ammonium phosphate
phosphate rock and sulfuric acid
Phosphate rock is treated with sulfuric acid to produce
single superphosphate
(mixture of calcium phosphate and calcium sulfate)
phosphate rock and phosphoric acid
Phosphate rock is treated with phosphoric acid to produce
triple superphosphate,
which is calcium phosphate
Where does the potassium used come from
The potassium salts, potassium chloride and potassium sulfate are mined from the ground. They are soluble in water, so they can be separated from impurities and used directly.
Advantage of using a formulation to make a fertiliser
Can make a fertiliser with specific properties
