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

(N/A) In the laboratory,nitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
The chemical equation for the reaction is:
$NH_4Cl_{(aq)} + NaNO_{2_{(aq)}} \to N_{2_{(g)}} + 2H_2O_{(l)} + NaCl_{(aq)}$
Small amounts of $NO$ and $HNO_3$ are produced as impurities. These can be removed by passing the nitrogen gas through an aqueous solution of sulphuric acid containing potassium dichromate.