18. Bismuth

1. $H_2S$ or $(NH_4)_2S$

$2Bi^{3+}$ $+$ $3S^{2-}$ $\longrightarrow$ $Bi_2S_3$ - Dark brown precipitate - Soluble in dilute mineral acids - Insoluble in $(NH_4)_2S$

2. $KOH$ or $NH_3$

$Bi^{3+}$ $+$ $3OH^-$ $\longrightarrow$ $Bi(OH)_3$ - White precipitate - Soluble in dilute mineral acids - Insoluble in excess reagent

3. Hydrolysis

$BiCl^{2+}$ $+$ $H_2O$ $\longrightarrow$ $2H^+$ $+$ $BiOCl$ - Bismuthyl chloride, - Bismuth oxychloride - White precipitate - Soluble in dilute mineral acids - Insoluble in tartaric acid (difference $Sb$.)

6. $SO_4^{2-}$

(start with very little sulfate) $Pb^{2+}$ $+$ $2SO_4^{2-}$ $\longrightarrow$ $PbSO_4$ - White precipitate - Soluble in $NH_3$/acetic acid. - Soluble in $NH_3$/tartaric acid. - Soluble in hot $HNO_3$ .

7. $CrO_4^{2-}$

$Pb^{2+}$ $+$ $CrO_4^{2-}$ $\longrightarrow$ $PbCrO_4$ - Yellow precipitate - Soluble in cold $KOH$ - Soluble in cold $HNO_3$.