JEE Chemistry 2023 Question with Solution

Given: The options are lead salts formed with $\text{Pb}^{2+}$ ions.

Find: Which formation is not a confirmatory test for $\text{Pb}^{2+}$ ions.

Confirmatory tests for lead commonly involve formation of characteristic precipitates:

$$\text{PbSO}_4$$

white precipitate,

$$\text{PbCrO}_4$$

yellow precipitate, and

$$\text{PbI}_2$$

yellow precipitate.

From the solution:

$$\text{Pb(NO}_3\text{)}_2$$

is soluble and colourless, so its formation is not used as a confirmatory test for $\text{Pb}^{2+}$ ion.

Therefore, the correct option is B.

Given:

• $\text{PbSO}_4$ — white precipitate
• $\text{PbCrO}_4$ — yellow precipitate
• $\text{PbI}_2$ — yellow precipitate
• $\text{Pb(NO}_3\text{)}_2$ — soluble

Find: Which compound does not serve as a confirmatory test for lead ion.

A confirmatory test requires formation of a characteristic, observable compound, usually an insoluble precipitate with a distinct appearance. The compounds $\text{PbSO}_4$, $\text{PbCrO}_4$, and $\text{PbI}_2$ satisfy this condition because they form visible precipitates.

However,

$$\text{Pb(NO}_3\text{)}_2$$

is a common soluble salt. Its formation does not give a characteristic precipitate and therefore does not confirm the presence of $\text{Pb}^{2+}$.

Hence, the formation that is not a confirmatory test is lead nitrate, so the correct option is B.