Question

The gases evolved on heating lead (II) nitrate crystals are :

• A. NO and \( O_2 \uparrow \)
• B. \( N_2 \) and \( NO_2 \)
• C. \( NO_2 \) and \( H_2 \)
• D. \( NO_2 \) and \( O_2 \)

Hint:

Thermal decomposition of metal nitrates:

• Most metal nitrates decompose to give metal oxide + \(NO_2\) + \(O_2\)
• Exception: Sodium and potassium nitrates give metal nitrite + \(O_2\)
• Lead nitrate gives brown fumes of \(NO_2\) and glowing splint test confirms \(O_2\)

Answer 1

The Correct Option is D

Step 1: Recall the thermal decomposition of lead nitrate.
When lead nitrate [Pb(NO\(_3\))\(_2\)] is heated, it undergoes thermal decomposition to produce lead oxide, nitrogen dioxide, and oxygen.
Step 2: Write the balanced chemical equation.
\[ 2Pb(NO_3)_2(s) \xrightarrow{\Delta} 2PbO(s) + 4NO_2(g) + O_2(g) \]
Step 3: Identify the gases evolved.
From the equation:

• Nitrogen dioxide (\(NO_2\)) - brown fumes
• Oxygen (\(O_2\)) - colorless and supports combustion

Step 4: Observations during the reaction.

• On heating lead nitrate crystals, brown fumes of nitrogen dioxide (\(NO_2\)) are evolved.
• Oxygen gas (\(O_2\)) is also produced.
• A yellow residue of lead oxide (PbO) remains in the test tube.

Step 5: Analysis of options.

• (A) NO and \( O_2 \): Incorrect. NO is not produced in this reaction.
• (B) \( N_2 \) and \( NO_2 \): Incorrect. Nitrogen gas (\(N_2\)) is not produced.
• (C) \( NO_2 \) and \( H_2 \): Incorrect. Hydrogen gas (\(H_2\)) is not produced.
• (D) \( NO_2 \) and \( O_2 \): Correct. Both gases are produced as shown in the balanced equation.

Final Answer: (D) \( NO_2 \) and \( O_2 \)