(ii) Alumina is dissolved in cryolite for electrolysis
instead of being electrolyzed directly.
Extraction of copper directly from sulphide ores is less
favourable than that from its oxide ore through reduction. [3
x 1]
Answer:
(i)
This
reaction is spontaneous at high temperature 
For this
reaction, 
thus
non-spontaneous. Also chromium has greater affinity for oxygen thus reduction
with carbon is not feasible, [1]
(ii)
Cryolite improves the electrical conductivity of the cell as 
is poor
conductor. Also this serves as an added impurity and lowers the melting point
of the mixture to about 1220 K. [1]
(iii)
Extraction of copper from sulphide ore involves
(a) Concentration
(b) Bessemerisation
(c) Electrolytic
reduction
But
extraction from oxide ore involve
(a) Concentration
(b) Reduction
[1]
This process
is thermodynamically feasible.
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