Chemistry - Salt Analysis Question with Solution | TestHub

Question Explanation: Identifying correct chemical reactions for various inorganic anions. Concept:

Qualitative Analysis of Acid Radicals.

Solution:

Statement 1 is correct: Mercury(II) nitrate reacts with soluble carbonates to form a brown precipitate of basic mercury(II) carbonate (3HgO·HgCO₃) rather than normal mercury carbonate.

Statement 2 is incorrect: Sodium nitroprusside gives a violet color with Na₂S (alkaline medium), but it does not react with H₂S gas directly as the medium must be alkaline for the complex to form.

Statement 3 is incorrect: FeCl₃ reacts with Na₂S₂O₃ to form a violet complex $[Fe(S_2{O}_3{)}_2{]}^{-}$ which is a four-coordinated complex (it quickly decomposes), not six-coordinated.

Statement 4 is correct: Nitrites (NO₂⁻) are decomposed by urea (NH₂CONH₂) or thiourea (NH₂CSNH₂) in acidic medium, evolving N₂ gas.

Reaction for Statement 1:

$$4H{g}^{2+}+4C{O}_3^{2{-}_{}}+3H_{2}O⟶HgC{O}_3.3HgO\downarrow +3C{O}_2+6H^{+}$$

Reaction for Statement 4:

$$CO{\left(N{H}_2\right)}_2^{}+2H_{}N{O}_2\to 2N_2+C{O}_2+3H_{2}O$$

Final Answer: (A) and (D)