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

To determine the gases evolved when lead (II) nitrate is heated, we need to analyze the decomposition reaction of lead (II) nitrate.

When lead (II) nitrate, \(\text{Pb(NO}_3\text{)}_2\), is heated, it undergoes thermal decomposition to form lead (II) oxide, nitrogen dioxide, and oxygen. The reaction is as follows:

\(\text{2Pb(NO}_3\text{)}_2 \rightarrow 2\text{PbO} + 4\text{NO}_2 + \text{O}_2\)

From the decomposition equation:

• \(\text{NO}_2\) (nitrogen dioxide) is one of the gases evolved.
• \(\text{O}_2\) (oxygen) is the other gas evolved.

Thus, the gases evolved when lead (II) nitrate crystals are heated are nitrogen dioxide and oxygen.

Now, let's review the options given in the question to confirm the correct answer:

• Option 1: NO and \(\text{O}_2\) - This is incorrect as NO is not evolved during the decomposition.
• Option 2: \(\text{N}_2\) and \(\text{NO}_2\) - This is incorrect as nitrogen gas is not evolved.
• Option 3: \(\text{NO}_2\) and \(\text{H}_2\) - This is incorrect as hydrogen gas is not a product.
• Option 4: \(\text{NO}_2\) and \(\text{O}_2\) - This is the correct answer, as both \(\text{NO}_2\) and \(\text{O}_2\) are evolved.

Therefore, the correct answer is Option 4: \(\text{NO}_2\) and \(\text{O}_2\).