Extraction of Metals - Result Question 88
####91. Answer the following questions briefly
(i) What is the actual reducing agent of haematite in blast furnace?
(ii) Give the equation for the recovery of lead from galena by air reduction.
(iii) Why is sodium chloride added during electrolysis of fused anhydrous magnesium chloride?
(iv) Zinc, not copper is used for the recovery of metallic silver from complex $\left[Ag(CN) _2\right]^{-}$, explain
(v) Why is chalcocite roasted and not calcinated during recovery of copper?
$(1987,5 M)$
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Solution:
- (i) Carbon monoxide :
(ii)
$$ \begin{aligned} C+O _2 & \longrightarrow CO \ CO+Fe _2 O _3 & \longrightarrow CO _2+Fe \ 2 PbS+3 O _2 & \longrightarrow 2 PbO+2 SO _2 \ 2 PbO+PbS & \longrightarrow 3 Pb+SO _2 \end{aligned} $$
(iii) To improve electrical conductivity of melt.
(iv) A metal which is much more electropositive than $Ag$ can only replace $Ag^{+}$completely from $\left[Ag(CN) _2\right]^{-}$as
$$ Zn+2\left[Ag(CN) _2\right\rceil \longrightarrow\left[Zn(CN) _4\right]^{2-}+2 Ag $$
(v) Chalcocite is a sulphide ore of copper, during roasting, $SO _2$ is liberated, which is not possible in calcination.
