O Level Chem: Nov 06/ Paper 3/ Section B/ Q11
(a)
(i) Iron is manufactured in a blast furnace using an iron ore, coke and limestone. Name a suitable iron ore.
(ii) Describe the essential chemical reactions that take place in the blast furnace. Include chemical equations in your description
(b) When a piece of magnesium is attached to an underground iron pipe the working life of the pipe is increase though not permanently.
(i) Explain this limited increase in the working life of the iron pipe.
(ii) If copper is used instead of magnesium, the lifetime of the iron pipe is not increased.
Explain why.
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Answer: (a)
(i) A suitable iron ore is Haematite (Fe2O3). Another is Magnetite (Fe304).
(ii)
The entire process that take place in the blast furnace is as follows:
Firstly, Coke (C) reacts with Oxygen (O2) in the air to form carbon dioxide. This is an exothermic reaction which produce more heat.
C+O2 -> CO2
The heat will cause a chain reaction to occur. Cardon dioxide will reacts with more coke to form carbon monoxide
CO2 + C -> CO.
Carbon monoxide is a reducing agent. It reacts with the Iron(III)Oxide to produce molten iron. Molten Iron, with its high density will be flow to the bottom of the blast furnace.
CO +Fe2O3 -> 2Fe + 3CO2
Limestone is added. It will be decomposed by the high temperature in the furnace to Calcium Oxide and Carbon Dioxide.
CaCO3 -> CaO + CO2
It acts to neutralised a lot of the acidic impurities that exists in Iron ore. For example silicon dioxide.
SiO2 + CaO -> CaSiO3
This is known as slag which will flow to the bottom of the furnace but stays on top of the molten iron. Slag can be used to make roads.
(b)(i)
This is known as sacrificial protection or Cathodic Protection.
The reactivity series is as follows:
Potassium Sodium Calcium Magnesium Aluminium Zinc Iron (Hydrogen) Tin Lead Copper Silver Gold Platinium.
Magnesium is above Iron in the reactivity series. Hence, it will react preferably with water. It acts as the cathode (Loses electrons) and hence is corrode preferably.
INFO:
If the reaction is taking place on the iron side, electrons will transfer from the magnesium to the iron and hence magnesium will be preferably oxidised.
(ii) Copper is below Iron in th reactivity series. Hence, it will not be preferably oxidised. Instead. Iron is now the cathode and hence will now rust faster due to the fact that Copper is less reactive than iron.
TIP:
To remember the reactivity series
Use This:
Please Potassium
Stop Sodium
Calling Calcium
Me Magnesium
A Aluminium
Zebra Zinc
Invent the rest yourself :P
