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Cadmium sulfide
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1. $H_2S$ or $(NH_4)_2S$ |
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$Cd^{2+}$ $+$ $S^{2-}$ $\longrightarrow$ $CdS$ - Lemon-yellow precipitate - Soluble in dilute mineral acids - Insoluble in $(NH_4)_2S$ |
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2. $KOH$ |
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$Cd^{2+}$ $+$ $2OH^-$ $\longrightarrow$ $Cd(OH)_2$ - White precipitate - Soluble in dilute mineral acids - Insoluble in excess reagent |
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3. $NH_3$ |
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$Cd^{2+}$ $+$ $2OH^-$ $\longrightarrow$ $Cd(OH)_2$ - White precipitate - Soluble in an excess of reagent: $Cd(OH)_2 +4NH_3 \longrightarrow Cd(NH_3)_4^{2+}+2OH^-$ - Tetramminecadmium - Soluble - Colorless |
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4. $KCN$ |
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$Cd^{2+}$ $+$ $2CN^-$ $\longrightarrow$ $Cu(CN)_2$ - White precipitate - Soluble in an excess of reagent: $Cu(CN)_2$ $+$ $2CN^-$ $\longrightarrow$ $Cd(CN)_4^{2-}$ - Tetracyanocadmiate - Soluble - Colorless - precipitated to $CdS$ by $H_2S$ as opposed to the copper tetracyano complex! |