Conversion of ore into Metal

Question 1 Name one ore of mercury and zinc?

Question 2 Give the chemical formula of ore of iron and copper?

Question 3 Name one metal which is extracted by reduction with carbon?

Question 4 Name one metal which is extracted by electrolytic reduction?

Question 5 Name one metal which is extracted by reduction with aluminium?

Question 6 How is copper extracted from copper glance. Give equations involved?

Question 7 How is mercury extracted from cinnabar. Give equations involved?

Question 8 Differentiate between calcination and roasting?

Question 9 How are the less reactive metals extracted?

Question 10 How are the highly reactive metals extracted?

Question 11 How does the method of extracting a metal from its ore depend on the position in the reactivity series?

Conversion of Ore into Metal

a) The less reactive metals are extracted by reduction of their oxides by heat alone.

For Example : Copper and mercury

 

1) Ore of mercury is cinnabar

Mercury oxide is reduced to mercury on heating.

HgS(s) + 3 O₂ (g) → 2 HgO (s) + 2 SO₂ (g)

2 Hg(s) → 2 Hg(l) +  O₂ (g)

2) Ore of copper is copper glance

2 Cu₂S (s)  + 3 O₂ (g) → 2 Cu₂O (s) + 2 SO₂  (g)

2 Cu₂O (s) + Cu₂S (s) → 6 Cu (s) + SO₂  (g)

b) Moderately reactive metals(Cu, Zn, Pb, Cu) are present as carbonate or sulphides in nature.

1) Concentrated ore is converted to metal oxide

The carbonate or sulphide ore is first converted to oxides by the process of calcination or roasting.

Calcination	Roasting
1) It is the process by which a carbonate ore is heated strongly in the absence of air to convert into metal oxide.	It is a process in which sulphide ore is heated in the presence of air to convert into metal oxide.
2) ZnCO3 → ZnO + CO2	2ZnS → 2ZnO+2 SO2 + 3 O2

2) Metal oxide are reduced to metal

They are extracted by the reduction of their oxides with C, Al, Ca or Na.

a) Reduction of metal oxide with carbon(Zn, Fe, Ni, Sn, Pb, Cu) as reducing agent
The metal oxide is mixed with carbon and heated in a furnace. Carbon reduces metal oxide to free metal.

ZnO(s) + C(s) → Zn(s) + CO(g)

b) Reduction of metal oxide with Aluminium

This is used as a reducing agent in those cases where metal oxide is of comparatively more reactivity metal than zinc. This is because a more reactive metal can displace a less reactive metal from its metal oxide to give free metal. Manganese and chromium metals are extracted by the reduction of their oxides with aluminium powder.

3 MnO₂ + 4Al → 3Mn + 2 Al₂O₃ +heat

Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat

The reduction of metal oxide to metal by using Al powder as reducing agent is called Thermite process.
These reactions are highly exothermic. Metals are produced in molten state.

c) Highly reactive metals(Na, K, Ca, Mg, Al)

The oxides of highly reactive metals are very stable and cannot be reduced by carbon or aluminium.
They are extracted by electrolytic refining of their of molten oxides or chlorides. It is brought about by passing electric current through molten salt. During electrolysis metals are deposited at cathode(negatively charged electrode)and chlorine is liberated at anode(positively charged electrode)

NaCl(l) → 2Na(s) + Cl₂ (g)
At cathode

Na⁺ + e^–→ Na
At anode

2Cl → Cl₂ + 2 e^–
Al₂O₃ (l) → 4 Al(s) +3 O₂ (g)
At Cathode

Al³⁺ + 3 e^{– _→} Al
At anode

2O^2-– 4 e^{– _→} O₂