Question

Identify A, B, and C in the given reaction sequence: \[ \text{A} \xrightarrow{\text{HNO}_3} \text{Pb(NO}_3)_2 \xrightarrow{\text{H}_2\text{SO}_4} \text{B} \rightarrow \text{C (Yellow ppt)}. \]

• A. PbCl$_2$, PbSO$_4$, PbCrO$_4$
• B. PbS, PbSO$_4$, PbCrO$_4$
• C. PbS, PbSO$_4$, Pb(CH$_3$COO)$_2$
• D. PbCl$_2$, Pb(SO$_4$)$_2$, PbCrO$_4$

Hint:

The reaction sequence involves the formation of lead nitrate, lead sulfate, and lead chromate. This is a typical sequence for testing the presence of lead in reactions with chromates.

Answer 1

The Correct Option is B

1. Examine reaction sequences:
   • Initial compound \(\text{A}\) reacts with nitric acid \(\text{HNO}_3\) to produce lead nitrate \(\text{Pb(NO}_3)_2\).
   • Lead nitrate \(\text{Pb(NO}_3)_2\) reacts with sulfuric acid \(\text{H}_2\text{SO}_4\) to yield \(\text{B}\), identified as lead sulfate \(\text{PbSO}_4\).
   • Compound \(\text{B}\) transforms to form a yellow precipitate, indicating the creation of lead chromate \(\text{PbCrO}_4\), denoted as \(\text{C}\).
2. Identify \(\text{A}\):
   • To produce lead nitrate upon reaction with nitric acid, \(\text{A}\) is most likely lead sulfide \(\text{PbS}\). The transformation \(\text{PbS} \xrightarrow{\text{HNO}_3} \text{Pb(NO}_3)_2\) can be balanced to demonstrate this.
3. Outline the complete reaction pathway:
   • Step 1: \(\text{PbS} \xrightarrow{\text{HNO}_3} \text{Pb(NO}_3)_2\)
   • Step 2: \(\text{Pb(NO}_3)_2 \xrightarrow{\text{H}_2\text{SO}_4} \text{PbSO}_4\)
   • Step 3: \(\text{PbSO}_4 \rightarrow \text{PbCrO}_4 \, \text{(yellow ppt)}\)
4. Evaluate Correct Option:
   • The sequence transforming \(\text{PbS}\) to \(\text{PbSO}_4\) and subsequently to the yellow precipitate \(\text{PbCrO}_4\) corresponds to the option: "PbS, PbSO$_4$, PbCrO$_4$".
5. Eliminate Incorrect Options:
   • Options including \(\text{PbCl}_2\) and \(\text{Pb(SO}_4)_2\) are unsuitable because \(\text{PbS}\) directly leads to \(\text{Pb(NO}_3)_2\) and \(\text{PbSO}_4\).

Therefore, the correct reaction sequence is represented by the option: PbS, PbSO$_4$, PbCrO$_4$.