Question

Predict the correct order of mobility of $B{e}^{2+}$, $M{g}^{2+},$ $S{r}^{2+}$ and $C{a}^{2+}$ions in aqueous medium.

• A. $B{e}^{2+}$>$M{g}^{2+}$ > $C{a}^{2+}$> $S{r}^{2+}$
• B. $B{e}^{2+}$< $M{g}^{2+}$ < $C{a}^{2+}$< $S{r}^{2+}$
• C. $B{e}^{2+}$> $M{g}^{2+}$ >$S{r}^{2+}$> $C{a}^{2+}$
• D. $M{g}^{2+}$< $B{e}^{2+}$< $S{r}^{2+}$< $C{a}^{2+}$

Answer 1

The correct option is B $B{e}^{2+}$< $M{g}^{2+}$ < $C{a}^{2+}$< $S{r}^{2+}$

Ionic mobility depends on the hydration of the ion in aqueous medium.

Smaller the size of the cation (high charge density), more the degree of hydration (more it is surrounded by water molecules), higher will be the hydrated radii and hence least will be mobility.

The order of the size (hydrated radii) for the given ions in aqueous medium is $B{e}^{2+}$>$M{g}^{2+}$ > $C{a}^{2+}$> $S{r}^{2+}$
$\therefore$ The order of ionic mobility will be
$B{e}^{2+}$<$M{g}^{2+}$ < $C{a}^{2+}$< $S{r}^{2+}$