Chemistry Q54 – NEET-UG 2023

Home Chemistry Basic Organic ChemistryQuestion #150

In Lassaigne’s extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with

F e^{3 +}

due to the formation of -

Clue 1 of 3: Lassaigne's Test

Lassaigne's test is a qualitative analysis method used to detect the presence of nitrogen, sulfur, and halogens in organic compounds.

🥷

Ninja Strategy•Recall Specific Test Products

Directly recall the specific complex formed in Lassaigne's test for the simultaneous presence of nitrogen and sulfur that produces a blood-red color with $F e^{3 +}$ ions.

🧠 Full Solution Path

Step 1: Understand Lassaigne's Test for N and S✦ Active

In Lassaigne's test, if an organic compound contains both nitrogen and sulfur, during fusion with sodium metal, sodium thiocyanate ( $N a S C N$ ) is formed. This is represented as: $N a + C + N + S \overset{fusion}{\to} N a S C N$ .

💡 Teacher's Secret Hint

This step is crucial for understanding the precursor to the colored complex.

Step 2: Identify the Reaction with

F e^{3 +}

ions○ Expand

The $S C N^{-}$ ions (from $N a S C N$ ) then react with $F e^{3 +}$ ions to form a blood-red colored complex. The reaction is: $F e^{3 +} + S C N^{-} \to [F e (S C N)]^{2 +}$ .

💡 Teacher's Secret Hint

The characteristic blood-red color is a key indicator for the presence of both N and S.

Step 3: Match the product with the given options○ Expand

Comparing the formed complex $[F e (S C N)]^{2 +}$ with the given options, option (4) matches the product responsible for the blood-red color.

💡 Teacher's Secret Hint

Pay close attention to the stoichiometry and charge of the complex.

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Chemistry Question 54 – NEET-UG 2023

Clue 1 of 3: Lassaigne's Test

🧠 Full Solution Path