(a) Name two metal s which occur in nature in free state as well as in combined state
(b) Name one ore of manganese. Which compound of manganese is present in this ore? Also write its chemical formula.
(c) A zinc ore on heating in air forms sulphur dioxide. Describe briefly any two stages involved in the conversion of this concentrated ore into zinc metal.
Answer :
(a) Copper and silver metals occur in nature in free as well as the combined state.
(b) One ore of manganese is pyrolusite. This is an oxide ore. Manganese dioxide is the compound present in pyrolusite. Its chemical formula is MnO2.
(c) If zinc ore forms sulphur dioxide on heating in the presence of air, it should be a sulphide ore, i.e., zinc blende (Zinc sulphide or ZnS).
Two stages involved in the conversion of this concentrated zinc blende to zinc metal are:
1. Roasting: Zinc blende ore is subjected to roasting, i.e., it is heated in the presence of excess air. This converts zinc sulphide ore to zinc oxide. The reaction involved is:
2ZnS(s)+3O2(g)Roasting (surplus of air)−−−−−−−−−−−−−−−→2ZnO(s)+2SO2(g)
2. Reduction: Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as a reducing agent and reduces zinc oxide to zinc metal.
ZnO(s)+C(s)reduction−−−−−→ZnO(s)+CO2(g)