CBSE Class 12 Chemistry Notes: Ores and Metallurgy - Summary of the Extraction of Metals and Illustrations

Summary of the Extraction of Metals

Some Important Illustrations to solve

Illustration 1.
The roasting of an ore of a metal usually results in conversion of the metal to the oxide. Why does the roasting of cinnabar, HgS, produce metallic mercury rather than an oxide of mercury?
Solution:
Since Hg lies much below in the electrochemical series hence HgO is further reduced to Hg.

HgS → HgO → Hg

Illustration 2.
Ore dressing of iron is done by
(A) froth floatation process (B) magnetic separation
(C) hand picking (D) all of the above

Solution: (C)

Illustration 3.
The flux used in extraction of iron is
(A) limestone (B) silica
(C) flint (D) feldspar

Solution: (A)

Illustration 4.
Impurities physically associated with minerals are
(A) slag (B) flux
(C) alloy (D) matrix
Solution: (D)

Exercise 5.
Which of the metals Na, Ag and Fe are extracted by complex formation?
(ii) Reduction with carbon (iii) Electrolysis of fused salt.
Answer : (i) Ag, (ii) Fe, (iii) Na

Exercise 6.
Which of the following metals is lightest and which of them is least reactive?
Cu, Fe, Ag, Al
Answer : Lightest element – Al, least reactive – Ag

Illustration 7.
Write short notes on the following?
(i) Hydrometallurgy (ii) Self reduction
Solution:
(i) Hydrometallurgy is the process of bringing the metal into solution by the action of suitable chemical reagents (e.g., sodium cyanide solution or chlorine in presence of water etc.) followed by recovery of the metal by the use of a proper precipitating agent which is a more electropositive metal. For example, the ore of silver is suspended in a dilute solution of sodium cyanide and air is blown through it when the silver present goes into the solution as the argentocyanide complex. From this solution the metal is precipitated by adding zinc turnings.

(ii) In some cases no extra reducing agent is required. A part of the sulphide ore is changed to oxide or sulphate which then reacts with the remaining part to give the metal and sulphur dioxide. Copper and lead are obtained by this method.