1 mole of PbS is oxidised by "X" moles of O₃ to get "Y" moles of O₂. X+Y= _________.

Solution

Chemistry ma’am · 4 steps

Each O₃ hands over just one O atom and leaves as O₂, so count the O atoms the sulphate needs.

1. How ozone oxidises. Ozone acts as an oxidant by splitting as O₃ → O₂ + [O]. Each O₃ gives one oxygen atom to the substance being oxidised, and its other two atoms leave as one O₂.
2. What PbS needs. PbS is oxidised to PbSO₄, so sulphur goes from -2 to +6. That needs 4 oxygen atoms. So 4 O₃ are used, and they release 4 O₂.

   PbS + 4O₃ → PbSO₄ + 4O₂

3. Check electrons. Sulphur loses 8 electrons. Each transferred O atom goes from 0 to -2 and takes 2 electrons, so 4 O atoms take 4 × 2 = 8. The electrons balance, and so do the atoms: 12 O on each side.
4. So. X = 4 and Y = 4, so X + Y = 8.

The common slip: 3. Balancing only the atoms as PbS + 2O₃ → PbSO₄ + O₂ gives 3. It looks balanced on paper, but ozone gives one O atom per molecule and releases the rest as O₂.

The idea to keep. In ozone oxidations, one O₃ gives one O atom and frees one O₂. So moles of O₃ used equal moles of O₂ formed, and both equal the O atoms added.

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