Section 5: Chemistry in Industry Flashcards
How do you extract a metal which is below carbon in the reactivity series?
React it with carbon or carbon monoxide. The carbon will displace the metal.
How do you extract a metal which is above carbon in the reactivity series?
Use electrolysis.
Describe and explain the extraction of aluminium from purified aluminium oxide by electrolysis.
1) Bauxite is purified into aluminium oxide.
2) Dissolved in molten cryolite
3) The walls of the tank are the negative electrode; here aluminium is made
4) The aluminium sinks to the bottom and is tapped off
5) Oxygen is formed at the positive electrode
Why is the purified aluminium oxide dissolved in molten cryolite?
To bring down the boiling point
Why do the anodes need to be replaced in the electrolysis of aluminium?
The oxygen formed reacts with the carbon anode to from carbon dioxide; so the anode has to be replaced.
What is the cost of the electricity like in the electrolysis of aluminium?
It is very expensive, because a lot of electricity is needed.
What is the half-equation at the cathode in the extraction of aluminium?
Al3+ + 3e- –> Al
What is the half-equation at the anode in the extraction of aluminium?
2O2- –> O2 + 4e-
What are the steps of the extraction of iron from iron ore?
Coke reacts with oxygen to form carbon dioxide. This is reduced by more carbon, to form carbon monoxide. Carbon monoxide reduces the haematite. The iron melts and flows to the bottom of the furnace and can be tapped off.
Why is limestone used in the extraction of iron?
It is added to the furnace to remove impurities in the ore which would clog the furnace with solid material. It decomposes to calcium oxide, and then reacts with the impurities to form slag, which flows to the bottom, but floats on top of the molten iron. It can be tapped off separately.
What is the reaction between the coke (reduced to carbon monoxide) and haematite?
Fe2O3 + 3CO –> 2Fe + 3CO2
What are the reactions between the calcium oxide (decomposed limestone) and the impurities to form slag?
CaO + SiO2 –> CaSiO3
Why is aluminium used in making aeroplanes?
As an alloy, the aluminium is strengthened. It resists corrosion and has a low density.
Why is aluminium used in making pans?
It has a shiny appearance, resists corrosion, has a low density and is a good conductor of heat.
Why is aluminium used in electric cables?
It resists corrosion, has a low density and is a good conductor of electricity. It is strengthened by a core of steel.
Why is cast iron used for things like manhole covers, guttering and drainpipes?
It is very fluid when it is molten, and does not shrink much when it solidifies. It is good for castings. However, it is very brittle.
Why is mild steel (an alloy of iron) used for wire, nails, car bodies, ship building and bridges?
Only has a small amount of carbon (0.25%). This is increases the hardness and strength of the iron.
What is stainless steel used for and why?
Cutlery, cooking utensils and kitchen sinks, because it is corrosion-resistant.
What is crude oil?
A mixture of hydrocarbons
How does the industrial process of fractional distillation separate crude oil intro fractions?
It is split in a fractionating column, with a temperature gradient (cooler at the top). This sorts the fractions by boiling point.
What are the names of the main fractions and some uses of each of them?
Refinery gases - cooking
Gasoline - petrol
Kerosene - aircraft fuel
Diesel - fuel for cars, lorries and buses
Fuel oil - fuel for ships and power stations
Bitumen - road tar
What are the trends in boiling point and viscosity?
As you go down the fractionating column, the boiling point and viscosity increase.
What are the problems associated with the incomplete combustion of fuels?
The incomplete combustion of fuels produces carbon monoxide, which is poisonous because it reduces the capacity of the blood to carry oxygen.
