Question

When a student put some copper turnings in a colourless solution, he observed that the solution gradually turned blue. The solution is most likely to be :
(1) ferrous sulphate solution
(2) magnesium nitrate solution
(3) silver nitrate solution
(4) copper sulphate solution

Answer 1

The silver nitrate solution is colourless in nature. When copper reacts with silver nitrate, it displaces silver from silver nitrate and forms copper nitrate solution, which is of blue colour.

$\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{AgNO}}_3\left(\mathrm{aq}\right)\to \underset{\mathrm{Blue}\mathrm{Colour}}{\mathrm{Cu}\left({\mathrm{NO}}_3{)}_2\right(\mathrm{aq})}+\mathrm{Ag}\left(\mathrm{s}\right)$

Hence, the correct answer is option 3.