Question

If the solubility of an electrolyte is S, then what is the solubility product of the electrolyte of the type $A_3B_2$ ?

• A. $6S^3$
• B. $27S^5$
• C. $108 S^5$
• D. $36S^5$

Answer 1

Answer: (C)

$ A_3 B_2 \rightleftharpoons 3A^{2+} + 2B^{3-}$
$K_{sp} = [A^{2+}]^3 [B^{3-} ]^2$
If $S$ = solubility of $A_3B_2$, then
$[A^{2+}] = 3S ; [B^{3-}] = 2S$
therefore, $K_{sp} = (3S)^3 \times (2S)^2$
          $= 27S^3 \times 4S^2$
          $ = 108 S^5$