Which salt on heating does not give brown coloured gas?

L i N O_{3}

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K N O_{3}

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P b N O_{3}

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A g N O_{3}

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Solution

The correct option is B $K N O_{3}$
The nitrates of lithium, silver and most divalent and trivalent metals on heating decompose to give reddish brown fumes of nitrogen dioxide and oxygen as the gaseous products.

$4$ $L i N O_{3}$ $\to$ $2$ $L i_{2} O$ + $4$ $N O_{2}$ + $O_{2}$

$2$ $A g N O_{3}$ $\to$ $2$ $A g$ + $2$ $N O_{2}$ + $O_{2}$

$H g (N O_{3})_{2}$ $\to$ $H g$ + $2$ $N O_{2}$ + $O_{2}$

$2$ $M g (N O_{3})_{2}$ $\to$ $2$ $M g O$ + $4 N O_{2}$ + $O_{2}$

$2$ $P b (N O_{3})_{2}$ $\to$ $2$ $P b O$ + $4$ $N O_{2}$ + $O 2$

$4$ $A l (N O_{3})_{3}$ $\to$ $2$ $A l_{2} O_{3}$ + $12$ $N O_{2}$ + $3$ $O_{2}$

But the nitrates of Sodium and other heavier alkali metals - Potassium, Rubidium and Caesium - do not liberate $N O_{2}$ on heating. They give only oxygen as the gaseous product and the respective nitrite is left as the solid residue.

$2$ $N a N O_{3}$ $\to$ $2$ $N a N O_{2}$ + $O_{2}$

$2$ $K N O_{3}$ $\to$ $2$ $K N O_{2}$ + $O_{2}$

Hence the correct option is 'B'.

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Similar questions

Choose the correct answer :

(a) The nitrate salt which does not give a mixture of $N O_{2}$ and $O_{2}$ on heating is :

(i) $A g N O_{3}$ , (ii) $K N O_{3}$ ,

(iii) $C u (N O_{3})_{3}$ , (iv) $Z n (N O_{3})_{2}$ .

(b) The chemical used in the brown ring test is :

(i) $C u S O_{4}$ , (ii) $F e S O_{4}$

(iii) $F e_{2} (S O_{4})_{3}$ (iv) $Z n S O_{4}$ .

(i) NO, (ii) $N_{2} O,$

(iii) $N O_{2}$ (iv) $N_{2} O_{5}$ .

[A g C l, M g C l_{2}, N a H S O_{4}, P b C O_{3}, Z n C O_{3}, K N O_{3}, C a (N O_{3})_{2}]

N O_{2}

N O_{2}

N H_{4} N O_{3}, K N O_{3}, N a N O_{2}, P b (N O_{3})_{2}, A g N O_{3}

A

B

C

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