Question

Sulphide ion $(S^{2-})$ reacts with solid sulphur forming $S^{2-}_2$ and $S^{2-}_3$ with formation constants 12 and 132 respectively. Formation constant of $S^{2-}_3$ from sulphur and $S^{2-}_2$ is :

• A. 12
• B. 132
• C. 132 x 12
• D. 11

Answer 1

Answer: (D)

11

Answer 2

(I) ${S^{2-} + S <=> S^{2-}_2 ; K_1 = 12 }$ (II) ${S^{2-} + S <=> S^{2-}_3 ; K_1 = 132 }$ (III) ${S^{2-}_2 + S <=> S^{2-}_3 ; K = ? }$ To get eqn. (III), subtract (I) from (II) K = $\frac{K_2}{K_1} = \frac{132}{12} = 11$