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

Step 1: The laboratory method.

Nitrogen gas is conveniently prepared in the laboratory by treating an aqueous solution of ammonium chloride with sodium nitrite and heating the mixture.

Here, $NH_4^+$ (containing N in $-3$ state) and $NO_2^-$ (containing N in $+3$ state) comproportionate to give $N_2$ (0 state).

Step 2: Purification.

The nitrogen gas obtained by this method contains some impurities of NO and $HNO_3$, which are removed by passing the gas through aqueous sulphuric acid containing potassium dichromate.

Step 3: Alternative small-scale reaction (also acceptable).

Very pure nitrogen can also be obtained by the thermal decomposition of ammonium dichromate: …

State the standard NCERT laboratory preparation (NH4Cl + NaNO2, heated), write the balanced equation, and optionally mention the purifi …

• Do not confuse this laboratory-scale preparation with the industrial Haber process (that makes ammonia, not nitrogen, and is asked in a separate question).
• Do not forget to balance the equation (2 H2O, matching both N and H/O/Na/Cl counts). …