Question

Three sparingly soluble salts that have same solubility products are given below:
$I.A_{2}XII.AXIII.A{X}_3$
Their solubilities in a standard solution will be such that:

• A. $III>II>I$
• B. $III>I>II$
• C. $II>III>I$
• D. $II>I>III$

Answer 1

Answer: (D)

$II>I>III$

$AX\rightleftharpoons A^{+}+X^{-}$

$S$ $S$

$K_{sp}=\left[A^{+}\right]\left[X^{-}\right]=\left(S\right)\left(S\right)=S^2$

$S=\sqrt{K_{sp}}$ for $AX$

$A_{2}X\rightleftharpoons 2A^{+}+X^{-}$

$2S$ $S$

$K_{sp}=\left[A^{+}{]}^2\right[X^{-}]=(2S{)}^2\left(S\right)=4S^3$

$S={\left[\frac{K_{sp}}{4}\right]}^{1/3}$ for $A_{2}X$

$A{X}_3\rightleftharpoons A^{+}+3X^{-}$

$S$ $3S$

$K_{sp}=\left[A^{+}\right][X^{-}{]}^3=(S\left)\right(3S{)}^3=27S^4$

$S={\left[\frac{K_{sp}}{27}\right]}^{1/4}$ for $A{X}_3$

Solubility order:$AX>A_{2}X>A{X}_3$