Which of the following reagents are used for the detection of acetate and oxalate ions respectively? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Ferrous hydroxide, Fe(OH)2, has a much larger solubility product (Ksp ~ 8 x 10^-16) compared to ferric hydroxide, Fe(OH)3 (Ksp ~ 4 x 10^-38). Step 2: In the Group III analytical buffer (NH4Cl/NH4OH), the hydroxide ion concentration is suppressed and is too low to completely precipitate Fe2+ as Fe(OH)2, whereas it is sufficient to completely precipitate Fe3+. Step 3: Therefore, the solution is boiled with concentrated HNO3 (a strong oxidizing agent) to oxidize any Fe2+ present to Fe3+, ensuring complete precipitation in Group III. This corresponds to option (b).