How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.

${\mathrm{NH}}_{4}{\mathrm{CI}}_{\left(\mathrm{aq}\right)}+{\mathrm{NaNO}}_{2\left(\mathrm{aq}\right)}\to {\mathrm{N}}_{2\left(\mathrm{g}\right)}+2{\mathrm{H}}_{2}{\mathrm{O}}_{\left(\mathrm{l}\right)}+{\mathrm{NaNI}}_{\left(\mathrm{aq}\right)}$NO and HNO3 are produced in small amounts. These are impurities that can be removed on passing nitrogen gas through aqueous sulphuric acid, containing potassium dichromate.