For the brown ring test, the correct order of the steps in the experiment is:

A. Pour conc. \(H_2SO_4\) very slowly along the side of the test tube, very few drops of the acid should be poured.

B. Take half spatula of the given salt in dry test tube

C. Add 2-3 mL of freshly prepared ferrous sulphate solution to the test tube.

D. Make a solution of the given salt

Choose the correct answer from the options given below:

B, D, C, A

The correct answer is option 1. B, D, C, A.

Let us go through each step of the brown ring test in detail to understand why the correct sequence is 1. B, D, C, A:

Preparation of the Salt Sample: B. Take half spatula of the given salt in a dry test tube

This step involves taking a small amount of the nitrate-containing salt. It’s a preparatory step to ensure that you have the sample you need to test. Ensures you have the right amount of the sample for dissolution.

Dissolving the Salt: D. Make a solution of the given salt

Dissolve the solid salt in water to create an aqueous solution. This is crucial because the test for nitrate ions requires the salt to be in solution so that it can react with other reagents. Ensures that the nitrate ions are available in the solution for the subsequent reactions.

Adding Ferrous Sulfate Solution: C. Add 2-3 mL of freshly prepared ferrous sulfate solution to the test tube

The ferrous sulfate solution reacts with the nitrate ions in the solution. Ferrous sulfate is used because it reacts with nitrates in the presence of sulfuric acid to form a brown ring complex. In the presence of concentrated sulfuric acid, ferrous sulfate reacts with nitrate ions to form a brown ring at the interface of the two layers. The reaction involves the reduction of nitrates to nitric oxide and the formation of a complex with ferrous ions. This step is essential to introduce the reagent that will form the observable brown ring if nitrate ions are present.

Adding Concentrated Sulfuric Acid: A. Pour conc. \(H_2SO_4\) very slowly along the side of the test tube, very few drops of the acid should be poured

Add concentrated sulfuric acid carefully to form a separate layer below the aqueous solution. This creates a distinct interface between the sulfuric acid and the aqueous solution. The brown ring forms at the interface of the two layers. The sulfuric acid must be added slowly to prevent mixing with the aqueous solution. This step helps to visualize the brown ring, which indicates the presence of nitrate ions in the solution.

Summary of the Test Procedure

Prepare the Sample: Take the nitrate-containing salt and prepare it for testing.

Dissolve the Sample: Create a solution of the salt to make nitrate ions available.

Add Ferrous Sulfate: Introduce ferrous sulfate to react with nitrate ions.

Add Sulfuric Acid: Carefully add concentrated sulfuric acid to form a distinct layer and allow the formation of a brown ring at the interface.

By following these steps in the correct order, you ensure that the test is conducted properly and the presence of nitrate ions can be detected effectively.