On reaction of Lead Sulphide with dilute nitric acid which of the following is not formed?

Solution

Chemistry ma’am · 4 steps

Dilute nitric acid oxidises the sulphide ion to sulphur and is itself reduced to NO, not to N₂O.

1. Two jobs of HNO3. Dilute HNO₃ acts as an acid and as an oxidising agent at the same time. As an acid it gives the salt Pb(NO₃)₂. As an oxidant it oxidises S²⁻ to yellow sulphur.
2. Reduction product. Dilute nitric acid is reduced from N in the +5 state to NO, with N in the +2 state. Each N gains 3 electrons, and each S²⁻ loses 2, so 3 PbS react for every 2 NO formed.

   3PbS + 8HNO₃ → 3Pb(NO₃)₂ + 2NO ↑ + 3S v + 4H₂O

3. Check the options. Sulphur, nitric oxide and lead nitrate all appear as products. Nitrous oxide, N₂O, would need N to go down to +1, and that does not happen in this reaction.
4. So. The product that is not formed is nitrous oxide, option (d).

The idea to keep. With metal sulphides, dilute HNO₃ gives metal nitrate, free sulphur and NO. Always balance the electrons lost by S against the electrons gained by N.

Answer from the NTA final answer key. Solution by PrepWiser.