JEE Advanced · Chemistry · 31. Practical Chemistry
A solution when diluted with \(\mathrm{H}_2 \mathrm{O}\) and boiled, it gives a white precipitate. On addition of excess \(\mathrm{NH}_4 \mathrm{Cl} / \mathrm{NH}_4 \mathrm{OH}\), the volume of precipitate decreases leaving behind a white gelatinous precipitate. Identify the precipitate which dissolves in \(\mathrm{NH}_4 \mathrm{OH} / \mathrm{NH}_4 \mathrm{Cl}\).
- A \(\mathrm{Zn}(\mathrm{OH})_2\)
- B \(\mathrm{Al}(\mathrm{OH})_3\)
- C \(\mathrm{Mg}(\mathrm{OH})_2\)
- D \(\mathrm{Ca}(\mathrm{OH})_2\)
Answer & Solution
Correct Answer
(A) \(\mathrm{Zn}(\mathrm{OH})_2\)
Step-by-step Solution
Detailed explanation
A solution of \(\mathrm{Zn}^{2+}\) ion reacts with water which on boiling give white ppt. of \(\mathrm{Zn}(\mathrm{OH})_2\). This precipitates dissolve in excess of \(\mathrm{NH}_4 \mathrm{OH}\) in presence of \(\mathrm{NH}_4 \mathrm{Cl}\) because \(\mathrm{Zn}(\mathrm{OH})_2\) on reaction with \(\mathrm{NH}_4 \mathrm{OH}\) in presence of \(\mathrm{NH}_4 \mathrm{Cl}\) forms tetrammine zinc (II) complex (soluble).
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