Question

Sulfide ion in alkaline solution reacts with solid sulfur to form polysulfide ions having formulae $S_2^{2-},S_3^{2-},S_4^{2-}$ and so on. The equilibrium constant for the formation of $S_2^{2-}$ is $12\left(K_1\right)$ & for the formation of $S_3^{2-}$ is $132\left(K_1\right)$, both from S and $S^{2-}$. What is the equilibrium constant for the formation of from $S_3^{2-}$ from $S_2^{2-}$ and S?

• A. 11
• B. 12
• C. 132
• D. None of these

Answer 1

The correct option is A 11

$S+S^{2-}\rightleftharpoons S_2^{2-}$ $K=12K_1\to \left(i\right)$

$2S+S^{2-}\rightleftharpoons S_3^{2-}$ $K^1=132K_1\to \left(ii\right)$

(ii) - (i) gives

$S_2^{2-}+S\rightleftharpoons S_3^{2-}$

$\begin{array}{c}{K}^{\prime \prime }=K^{\prime }/k\Rightarrow \frac{132K_1}{12K_1}\Rightarrow 11\\ K^{\prime \prime }=11\end{array}$

Option A is correct.