Question

suppose you have a solution that might contain any or all of the following cations: Cu2+, Ag+,Ba2+ and Mn2+. The addition of HBr causes a precipitate form. after the precipitate is separated by filtration, H2SO4 is added to the supernatant liquid, and another precipitate forms.

Answer 1

The solution formed a precipitate when HBr is added. This indicates that the cation present would be silver ion(Ag$^{+}$) as silver forms an insoluble precipitate with bromide ion.

The equation representing the formation of silver bromide precipitate is:

$Ag^{+}(aq)+HBr(aq)-->AgBr(s)+H^{+}(aq)$

Bromides of all the other cations,$Cu^{2+},Ag^{+},Ba^{2+},Mn^{2+}$are soluble in aqueous solutions.

After removing the precipitate of AgBr by filtration, the supernatant solution is treated with $H_{2}SO_{4}$and another precipitate forms. This would be due to the presence of $Ba^{2+}$ions as barium sulfate is an insoluble precipitate.

The equation representing the formation of barium sulfate precipitate is:

$Ba^{2+}(aq)+H_{2}SO_{4}(aq)-->BaSO_{4}(s)+2H^{+}(aq)$

Answer 2

Of the given cations, only Ag+ forms both an insoluble bromide and sulfate, leading to precipitatoin; therefore, the ion present must be Ag+.