Question

Why the solution of silver nitrate turns blue in colour after some time when copper turning are added to it?

Answer 1

Displacement reaction: A reaction in which a more active element displaces a less active element from a compound is known as a displacement reaction.

$\underset{\mathrm{zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{zinc}\mathrm{sulphate}}{{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

When copper turnings are added to a solution of silver nitrate it turns blue due to the formation of copper nitrate i.e. copper being a more active metal displaces silver from its solution and forms copper nitrate.

$\underset{\mathrm{siver}\mathrm{nitrate}}{{\mathrm{AgNO}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}\to \underset{\mathrm{silver}}{\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{copper}\mathrm{nitrate}}{{\mathrm{CuNO}}_3\left(\mathrm{aq}\right)}$

This is an example of a displacement reaction.