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ChemistryNumerical+3Question 26 of 54

JEE Advanced 2018 · Paper 2, Chemistry question 8

Galena (an ore) is partially oxidized 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 contents undergo self-reduction. The weight (in kg) of Pb produced per kg of O2\mathrm{O_2} consumed is ____.

(Atomic weights in g mol−1^{-1}: O = 16, S = 32, Pb = 207)

Answer and worked solution

Official answer: 6.4

Partial roasting.
2 PbS+3 OX2→2 PbO+2 SOX2\ce{2PbS + 3O2 -> 2PbO + 2SO2}

Self-reduction.
PbS+2 PbO→3 Pb+SOX2\ce{PbS + 2PbO -> 3Pb + SO2}

Net. Adding the two gives 3 PbS+3 OX2→3 Pb+3 SOX2\ce{3PbS + 3O2 -> 3Pb + 3SO2}, i.e. one mole of Pb per mole of OX2\ce{O2}:
20732=6.47 kg of Pb per kg of OX2.\frac{207}{32}=6.47\text{ kg of Pb per kg of }\ce{O2}.

Answer: 6.47 (key: 6.40 to 6.50)

Topics:Extraction of specific metalsStoichiometry
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