Some Basic Concepts of Chemistry - Result Question 32
33. Galena (an ore) is partially oxidised by passing air through it at high temperature. After some time, the passage of air is stopped, but the heating is continued in a closed furnace such that the content undergo self-reduction. The weight (in kg ) of Pb produced per $\mathrm{kg} \mathrm{of}_2$ consumed is $\ldots \ldots \ldots$.
(Atomic weights in $\mathrm{g} \mathrm{mol}^{-1}: \mathrm{O}=16, \mathrm{~S}=32, \mathrm{~Pb}=207$ )
(2018 Adv.)
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Answer:
Correct Answer: 33. (6.47kg)
Solution:
- The equations of chemical reactions occurring during the process are In the presence of oxygen
$2 \mathrm{PbS}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{PbO}+2 \mathrm{SO}_2 \hspace {10mm}…(i)$
By self reduction
$2 \mathrm{PbO}+\mathrm{PbS} \longrightarrow 3 \mathrm{~Pb}+\mathrm{SO}_2$
Thus 3 moles of $\mathrm{O}_2$ produces 3 moles of Pb i.e. $32 \times 3=96 \mathrm{~g}$ of $\mathrm{O}_2$ produces $3 \times 207=621 \mathrm{~g}$ of Pb
So $1000 \mathrm{~g}(1 \mathrm{~kg})$ of oxygen will produce
$\begin{aligned} \frac{621}{96} \times 1000 & =6468.75 \mathrm{~g} \\ & =6.4687 \mathrm{~kg} \approx 6.47 \mathrm{~kg} \end{aligned}$
Alternative Method From the direct equation,
$\mathrm{PbS}+\underset{32 \mathrm{~g}}{\mathrm{O}_2} \longrightarrow \underset{207 \mathrm{~g}}{\mathrm{~Pb}}+\mathrm{SO}_2$
So, 32 g of $\mathrm{O}_2$ gives 207 g of Pb 1 g of $\mathrm{O}_2$ will give $\frac{207}{32} \mathrm{~g}$ of Pb 1000 g of $\mathrm{O}_2$ will give $\frac{207}{32} \times 1000=6468.75 \mathrm{~g}$
$=6.46875 \mathrm{~kg} \approx 6.47 \mathrm{~kg}$
BETA
