Question

The method by which very pure nitrogen can be obtained is

• A. Thermal decomposition of ammonium dichromate
• B. Thermal decomposition of barium azide
• C. Reaction of aqueous ammonium chloride with sodium nitrite
• D. Thermal decomposition of ammonium nitrate

Hint:

Pure gases are best obtained from reactions where all byproducts except the desired gas remain in the solid state.

Answer 1

The Correct Option is B

Step 1: Know the test for purity.
Very pure nitrogen comes from a reaction where nitrogen is the only gas formed. Any other gas would mix in and lower purity.
Step 2: Look at barium azide.
Heating barium azide gives $Ba(N_3)_2\rightarrow Ba+3N_2$.
Step 3: Check the products.
Barium stays as a solid and nitrogen is the only gas, so the nitrogen is extremely pure.
Step 4: Reject ammonium dichromate.
Its decomposition gives $N_2$ but also water vapour, so the gas is not pure.
Step 5: Reject ammonium chloride with sodium nitrite.
This makes nitrogen but also water and can carry small amounts of nitrogen oxides, so it is not the purest.
Step 6: State the answer.
\[ \boxed{\text{Thermal decomposition of barium azide}} \]