Question

The reaction of sulphur in alkaline medium is given below: $S_8(s) + a OH^-(aq) \to b S^{2-}(aq) + c S_2O_3^{2-}(aq) + d H_2O(l)$ The value of 'a' is __________. (Integer answer)

Hint:

Sulfur, Phosphorus ($P_4$), and Halogens ($Cl_2$) all undergo disproportionation in concentrated alkali.

Answer 1

Correct Answer: 12

Step 1: Sulfur undergoes disproportionation in alkaline medium.
Step 2: Balance $S$ atoms and charge: $S_8 + 12 OH^- \to 4 S^{2-} + 2 S_2O_3^{2-} + 6 H_2O$.
Step 3: Checking the charge: LHS is $-12$. RHS is $4(-2) + 2(-2) = -12$.
Step 4: Checking $H$ and $O$: 12 $H$ and 12 $O$ on LHS; 12 $H$ and $(2 \times 3 + 6) = 12$ $O$ on RHS.
Step 5: Comparing with the equation, $a = 12$.