Question

The hydroxide insoluble in $ NH_{4}OH + NH_{4}Cl $ is

• A. $ Al(OH)_{3} $
• B. $ Ca(OH)_{3} $
• C. $ Zn(OH)_{2} $
• D. $ Mg(OH)_{2} $

Answer 1

Answer: (A)

In qualitative analysis of basic radicals (cations only the hydroxides of IIIrd group radicals are insoluble in excess of $NH_{4}OH$ solution)
When aluminum salt reacts with $NH_{4}OH$, then a white ppt of $Al(OH)_{3}$ is obtained which is insoluble in excess of $NH_{4}OH$ solution
$AlCl_{3} + 3NH_{4}OH \to 3NH_{4}Cl + \underset{\text{white ppt}}{{Al(OH)_{3}}}$
The hydroxide of iron, chromium and aluminium are insoluble in excess of $NH_{4}OH$ solution