Question

In the precipitation of the iron group in qualitative analysis, ammonium chloride is added before adding ammonium hydroxide to:

• A. decrease concentration of $O{H}^{-}$ ions
• B. prevent interference by phosphate ions
• C. increase concentration of $C{l}^{-}$ ions
• D. increase concentration of $N{H}_4^{+}$ ions

Answer 1

The correct option is A decrease concentration of $O{H}^{-}$ ions

Iron belongs to $3^{rd}$ group and their hydroxides have low solubility product. Hence ${NH}_{4}Cl$ is added before adding ${NH}_{4}OH$ due to common ion effect so that only $3^{rd}$ group cations are precipitated.