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Colour and Solubility

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Question

From the formulae listed below, choose, one, corresponding to the salt having the given description:
AgCl, CuCO₃, CuSO₄.5H₂O, KNO₃, NaCl, NaHSO₄, Pb(NO₃)₂, ZnCO₃, ZnSO₄.7H₂O. On heating this, salt changes from green to black.

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Solution

On heating, the salt that will change from green to black is CuCO₃. Due to formation of CuO and evolution of CO₂ gas:

CuCO₃ $\overset{Δ}{\to}$ CuO + CO₂
Green Black

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Similar questions

From the formula listed below, choose one, in each case, corresponding to the salt having the given description:-

$A g C l, C u C O_{3}, C u S O_{4} .5 H_{2} O, K N O_{3}, N a C l, N a H S O_{4}, P b (N O_{3})_{2} . Z n C O_{3}, Z n C O_{4} .7 H_{2} O .$

(a) an acid salt.

(b) an insoluble chloride.

(d) on heating, this salt changes from green to black.

(e) this salt given nitrogen dioxide on heating.

[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}]

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) $N_{2} O_{5}$ .

14.3

1

N a = 23, H = 1, C = 12, O = 16)

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