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Galena, a lead ore, undergoes partial oxidation when air is passed through it at elevated temperatures. Afterward, air flow is stopped, and heating continues in a sealed furnace, allowing self-reduction to occur. What is the mass (in kg) of lead formed per kilogram of oxygen used? (Atomic masses in g/mol: O = 16, S = 32, Pb = 207)

1. 6.47
2. 5.47
3. 7.47
4. 4.47

Correct answer: 6.47

Solution

In the self-reduction process of galena (PbS), oxygen reacts with lead sulfide to form lead and sulfur dioxide. The stoichiometry of the reaction shows that 1 mole of oxygen (32 g) produces 6.47 moles of lead (207 g/mol). Thus, the mass of lead formed per kilogram of oxygen used is 6.47 kg.

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