Question

When a solution of mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in acidic medium, a dark brown ferric ion was formed when treated with ferric chloride. It gave deep red colour which disappeared on boiling and a brown red ppt was formed. The mixture contains:

• A. CO\(_3^{2-}\) & NO\(_3^{-}\)
• B. SO\(_4^{2-}\) & CH\(_3\)COO\(^-\)
• C. CH\(_3\)COO\(^-\) & FeCl\(_3\)
• D. SO\(_4^{2-}\) & CH\(_3\)COO\(^-\)

Hint:

When testing for specific ions in inorganic salts, observe changes in colour and precipitate formation which can give clues about the compounds involved.

Answer 1

The Correct Option is C

To solve this question, we need to identify the two inorganic salts present in the mixture, based on the given chemical reactions and observations:

1. The mixture, when treated with freshly prepared ferrous sulfate in acidic medium, results in the formation of a dark brown ferric ion.
2. Upon treatment with ferric chloride, it produces a deep red color which disappears upon boiling, resulting in a brown red precipitate.

We need to analyze the reactions step by step:

1. Nitrate Ion Detection (NO\(_3^-\)): One of the tests for nitrate ions involves treating it with freshly prepared ferrous sulfate and concentrated sulfuric acid (brown ring test). However, this is not consistent with the ferric ion formation or the color observations described as the test reactions do not align perfectly with all observations.
2. Acetate Ion (CH\(_3\)COO\(^{-}\)) Reaction: When ferric chloride reacts with acetate ions, it forms a deep red color due to the complex formation of ferric acetate, which disappears upon boiling due to the breakdown of this complex.
3. The reaction of ferric ion with acetate can be simplified as:
   \(Fe^{3+} + 3CH_3COO^- \rightarrow Fe(CH_3COO)_3\) (red complex)

The formation of the red complex, which disappears on boiling, is a characteristic test for acetate ions. Thus, the observations confirm the presence of acetate ions (CH\(_3\)COO\(^{-}\)) in the mixture.

Since the other condition involves the formation of ferric ion, it indicates the presence of FeCl\(_3\) in the solution.

Given this detailed analysis, the correct answer is the combination of acetate ions and ferric chloride, matching the provided option:

Correct Answer: CH\(_3\)COO\(^-\) & FeCl\(_3\)