Question

Sulfide ion in alkaline solution reacts with solid sulfux to form polysulfide ions having formules $S_2^{-2},S_3^{2-},S_4^{2-}$ and so on. The equilibrium constant for the formation of $S_2^{2-}$ is $12\left(K_5\right)$ & for the formulation of $S_3^{2-}$ is $132\left(K_2\right)$, both from S and $S^{2-}$. What is the equilibrium content for the formation of $S_3^{2-}$ from $S_2^{2-}$ and S?

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

Answer 1

The correct option is A $11$

$S+S^{2-}\to S_{2-}^2$ $k_1=12$

So, $12=\frac{\left[S_2^{2-}\right]}{\left[S^{2-}\right]}$ $............\left(1\right)$

$S+S^{2-}\to S_3^{2-}$ $k_2=132$

So, $132=\frac{\left[S_3^{2-}\right]}{\left[S^{2-}\right]}$ $............\left(1\right)$

For $S+S_2^{2-}\leftrightarrow S_3^{2-}$ $k_3$$=\frac{\left[S_3^{2-}\right]}{\left[S_2^{2-}\right]}$

By dividing (1) and (2),

$\frac{k_2}{k_1}=k_3=\frac{132}{12}=11$

Hence, equilibrium constant is 11.