JEE Advanced · 2018 · 20 May 2018 · Paper 2 · General Principles and Processes of Isolation of Metals

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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

O_{2}

consumed is ____.

(Atomic weights in

g mol^{- 1}

O = 16

S = 32

Pb = 207

)

Answer: 6.47

Solution

Galena is PbS. The overall process is:

2 PbS + 3 O_{2} \to 2 PbO + 2 SO_{2}

(oxidation), followed by

2 PbO + PbS \to 3 Pb + SO_{2}

(self-reduction). Combining:

3 PbS + 3 O_{2} \to 3 Pb + 3 SO_{2}

. From stoichiometry: 3 moles of

O_{2}

(96 g) produce 3 moles of Pb (621 g). Per kg of

O_{2}

\frac{621}{96} = 6.47

kg of Pb.

JEE Advanced · 2018 · 20 May 2018 · Paper 2 · Numerical answer

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JEE Advanced · 2018 · 20 May 2018 · Paper 2 · General Principles and Processes of Isolation of Metals

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