(a) Which metal is extracted from calamine ore?
(b) Name one ore of mercury. Which mercury compound is present in this ore? Write its chemical formula.
(c) How is copper extracted from its sulphide ore (copper glance), Cu2S? Explain with equations of the reactions involved.
(d) What is an alloy? Give two examples of alloys.
(e) How are the properties of an alloy different from those of the constituent elements?
(a) Zinc
(b) Cinnabar; Mercury (II) sulphide, HgS
(c) The concentrated copper (I) sulphide ore (copper glance), Cu2S is roasted in air when a part of copper (I) sulphide is oxidised to copper (I) oxide.
2Cu2S(s) + 3O2(g) + Roasting → 2Cu2O(s) + 2SO2(g)
When a good amount of copper (I) sulphide has been converted to copper (I) oxide, then the supply of air for roasting is stopped. In the absence of air, copper (I) oxide formed above reacts with remaining copper (I) sulphide to form copper metal and sulphur dioxide.
2Cu2S(s) + 3O2(g) + Roasting → 2Cu2O(s) + 2SO2(g)
(d) An alloy is a homogeneous mixture of two or more metals (or a metal and small amounts of non-metals).
Steel and Brass are examples of alloys.
(e) (i) Alloys are stronger than the metals from which they are made.
(ii) Alloys are harder than the constituent metals.
(iii) Alloys are more resistant to corrosion.
(iv) Alloys have lower melting points than constituent metals.
(v) Alloys have lower electrical conductivity than pure metals.