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Standard X

Chemistry

pH of Salts

A coloured pr...

Question

A coloured precipitate is obtained when $H_{2} S$ gas is passed through an aqueous solution of a salt in the presence of ammonium hydroxide. The precipitate dissolves in dilute $H C l$ and reacts with $N a O H$ to give white precipitate which on standing turns into a brown/black mass. The brown/black mass on fusion with $K N O_{3}$ and $N a_{2} C O_{3}$ gives green mass. The cation of the salt is:

C o^{2 +}

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M g^{2 +}

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N i^{2 +}

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M n^{2 +}

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Solution

The correct option is D $M n^{2 +}$
It is given that a colored precipitate is obtained when $H_{2} S$ gas is passed through an aqueous solution of salt in the presence of ammonium hydroxide. The precipitate dissolves in dilute $H C l$ and reacts with $N a O H$ to give white precipitate which on standing turns into a brown/black mass. The brown/black mass on fusion with $K N O_{3}$ and $N a_{2} C O_{3}$ gives green mass. The cation of the salt is $M n^{2 +}$ .

The reactions are given below:
$(1)$ $M n^{2 +} + H_{2} S \to M n S ↓ (buff coloured) H C l - - \to M n C l_{2}$ $N a O H - --- \to [O] M n O_{2} ↓ (brown/black)$

$(2)$ $M n O_{2} + 2 K N O_{3} + N a_{2} C O_{3} + H_{2} O fusion - -- \to$ $N a_{2} M n O_{4} (green mass) + 2 K N O_{2} + 2 N a O H + C O_{2}$

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