Question

During the qualitative analysis of a mixture containing ${Cu}^{2+}$ and ${Zn}^{2+}$ ions, which gas is passed through an acidified solution containing these ions in order to test ${Cu}^{2+}$ alone.

• A. $C{O}_2$
• B. $O_2$
• C. $H_{2}S$
• D. $S{O}_2$

Answer 1

The correct option is C $H_{2}S$

Test for $C{u}^{2+}:$ When the mixture containing $C{u}^{2+}$ and $Z{n}^{2+}$ ions are treated with the acid $HCl$, then following reaction take place with $C{u}^{2+}$.

$C{u}^{2+}+HCl\to CuC{l}_2+2H^{+}$

Then, when the $H_{2}S$ gas is passed to mixture solution then following reaction takes place.

$CuC{l}_2+H_{2}S\to CuS$ ( black ppt.) $+2HCl$

So, now we can say that when a mixture containing $C{u}^{2+}$ and $Z{n}^{2+}$ ions is acidified and further when $H_{2}S$ gas is passed to it only the $C{u}^{2+}$ ion gives a positive test.

Option C is correct.