During Group III cation analysis, solid is added before adding . The role of is to: — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

The common ion ($NH_4^+$) from the strong electrolyte $NH_4Cl$ suppresses the ionization of the weak base $NH_4OH$. This keeps the $OH^-$ concentration low enough to only precipitate the highly insoluble Group III hydroxides ($Fe, Al, Cr$).