4. Sulfate

1. $Ba^{2+}$ (Barium chloride)

$SO_4^{2-}+Ba^{2+}$ $\longrightarrow$ $BaSO_4$ - White precipitate - Insoluble in $HCl$ The search for the sulfate ion must be conducted by $BaCl_2$ in the presence of $HCl$. Indeed, in a neutral medium, the reagent also provides precipitates with the following anions: sulfite, carbonate, borate, phosphate, oxalate, tartrate. All these precipitates are soluble in $HCl$

2. $Pb^{2+}$ (Lead nitrate)

$SO_4^{2-}+Pb^{2+}$ $\longrightarrow$ $PbSO_4$ (-> lead sulfate, white precipitate, see →     cation $Pb^{2+}$)