Question

When an aqueous solution of gas $\left(X\right)$ is added in excess to a copper sulphate solution, a deep blue color is obtained, then gas is :

• A. $C{H}_{3}COOH$
• B. $N{H}_3$
• C. $S{O}_2$
• D. None of these

Answer 1

The correct option is B $N{H}_3$

When ammonia solution is added to solution of $C{u}^{2+}$, a blue precipitate of a basic copper sulphate is obtained, which is soluble in excess reagent giving deep-blue colouration of tetreamminecopper (II) sulphute.

'

$2C{u}^{2+}+S{O}_4^{2-}+2N{H}_3+2H_{2}O\to \underset{Blueppt}{Cu(OH{)}_2.CuS{O}_4\downarrow }+2N{H}_4^{+}$

$Cu(OH{)}_2.CuS{O}_4\downarrow +8N{H}_3\underset{Deep-bluecolouration}{\to 2\left[Cu\right(N{H}_3{)}_4{]}^{2+}+S{O}_4^{2-}}+2O{H}^{-}$

Then $X$ is $N{H}_3$.

Hence ,option B is correct.