Which of the following statements is/are TRUE regarding the precipitation of Group III basic radical — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

$NH_4Cl$ suppresses $NH_4OH$ ionization (common ion effect), keeping $[OH^-]$ low enough to precipitate only Group III hydroxides ($Fe, Al, Cr$) and preventing $Mg(OH)_2$ precipitation. $HNO_3$ oxidizes $Fe^{2+}$ to $Fe^{3+}$ because $Fe(OH)_2$ would not precipitate fully at this low $[OH^-]$. $NaOH$ cannot be used because it provides too much $[OH^-]$, precipitating higher groups.