Question

Separate samples of a solution of an unknown soluble ionic compound are treated with $\mathbf{KCl}\mathbf{,} {\mathbf{Na}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}\mathbf{,} \mathbf{and} \mathbf{NaOH}$. A precipitate forms only when${\mathbf{Na}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$ is added. Which cations could be present in the unknown soluble ionic compound?

Short answer

For the given cations, possible ions are ${\text{Ca}}^{\text{2 +}} \text{and} {\text{Ba}}^{\text{2 +}}$

Step-by-step solution

Definition of cation

The ion in an electrolyzed solution that migrates to the cathode broadly is defined as cation

Find which cations present in the unknown soluble ionic compound

${\text{Cl}}^{-}$Can only form precipitate with ${\text{Ag}}^{\text{+}}{\text{,Hg}}^{\text{2 +}}\text{,} \text{and} {\text{Pb}}^{\text{2 +}}$

${\text{SO}}_{\text{4}}^{\text{2 -}}$forms precipitate with ${\text{Ca}}^{\text{2 +}}{\text{,Sr}}^{\text{2 +}}{\text{,Ba}}^{\text{2 +}}{\text{,Hg}}^{\text{2 +}} \text{and} {\text{Pb}}^{\text{2 +}}$

${\text{OH}}^{-}$doesn’t form precipitate with ${\text{Ca}}^{\text{2 +}}{\text{,Sr}}^{\text{2 +}}{\text{,Ba}}^{\text{2 +}}$

From the above cations, possible ions can be role="math" localid="1651149846326" ${\mathbf{Ca}}^{\mathbf{2}\mathbf{+}} \mathbf{and} {\mathbf{Ba}}^{\mathbf{2}\mathbf{+}}$