Question

Consider the following compounds
1. \((NH_4)_2Cr_2O_7\) 2. \(NH_4NO_2\) 3. \(NH_4VO_3\) 4. \(NH_4NO_3\)
Which compound(s) yield nitrogen gas upon heating?

• A. 1 and 2
• B. 2 and 3
• C. 3 and 4
• D. 1 and 4
• E. All

Hint:

Ammonium nitrite is so unstable that it is usually prepared in situ (in the reaction mixture) because dry heating can be explosive.

Answer 1

The Correct Option is A

Concept: The thermal decomposition of ammonium salts depends on the nature of the anion. Salts containing oxidizing anions typically yield \(N_2\) or \(N_2O\).

Step 1: Analyze Compound 1 and 2.

• Ammonium Dichromate \((NH_4)_2Cr_2O_7\): Decomposes to yield nitrogen gas, water, and green chromic oxide. \[ (NH_4)_2Cr_2O_7 \xrightarrow{\Delta} N_2 + 4H_2O + Cr_2O_3 \]
• Ammonium Nitrite \(NH_4NO_2\): Readily decomposes into nitrogen gas and water. \[ NH_4NO_2 \xrightarrow{\Delta} N_2 + 2H_2O \]

Step 2: Analyze Compound 4.
Ammonium Nitrate (\(NH_4NO_3\)) decomposes at moderate temperatures to yield nitrous oxide (\(N_2O\)), not nitrogen gas (\(N_2\)). \[ NH_4NO_3 \xrightarrow{\Delta} N_2O + 2H_2O \]

Step 3: Conclusion.
Only 1 and 2 yield nitrogen gas (\(N_2\)).