Question 5 Answer
(a) Very reactive metals: K, Na, Ca, Mg, Al form stable ions which are difficult to reduce. They require a powerful method of reduction-electrolysis of their molten ores.
Less reactive metals: Zn, Fe, Pb form less stable ions which are difficult to reduce.
These need a less powerful method of reduction-heating the oxide ore with the reducing agents carbon in the form of Coke) or carbon monoxide.
Least reactive metals: Cu, Hg, Ag, Au usually occur as free element since their ions are very unstable.
They may however be extracted from their ores by heating the ore in air at high temperatures.
Dried heated iron ore, limestone and coke are fed into the top of the furnace.
Hot air is blown into the furnace near the bottom. The coke burns in the blast of hot air producing carbon dioxide and heat.
C (s) + O2 (g) → CO2 (g)
The Carbon dioxide formed is reduced to carbon monoxide by the hot coke:
CO2 (g) + C (s) → 2CO (g)
The Carbon Monoxide reduces the hot iron ore to molten iron:
Fe2O3 (s) + 3CO (g) → 2Fe (l) + 3CO2 (g)
Fe3O4 (s) + 4CO (g) → 3Fe (l) + 4 CO2 (g)
The molten Iron runs to the bottom of the furnace.
(c) Silica is an impurity in the ore.
It reacts with the by-product of limestone calcium oxide.
CaCO3 (s) → CaO (s) + CO2 (g)
CaO (s) + SiO2 (s) → CaSiO3 (l) – molten slag
(d) It is used for :
railings, grates, hot water pipes
Hard, Inexpensive, easy to cast into exact shape, Brittle