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\mathrm{Al}^{3+}, \mathrm{Fe}^{3+}, \mathrm{Zn}^{2+} \text{and}\: \mathrm{Ni}^{2+} ions are present in an acidic solution. Excess of ammonium chloride solution is added followed by addition of ammonium hydroxide solution. The available precipitate will contain

Option: 1

\mathrm{Zn}(\mathrm{OH})_{2}\text{ and }\mathrm{Ni}(\mathrm{OH})_{2}


Option: 2

\mathrm{Al}(\mathrm{OH})_{3}\text{ and }\mathrm{Fe}(\mathrm{OH})_{3}


Option: 3

\mathrm{Zn}(\mathrm{OH})_{2}\text{ and }\mathrm{Al}(\mathrm{OH})_{3}


Option: 4

\mathrm{Ni}(\mathrm{OH})_{2}\text{ and }\mathrm{Fe}(\mathrm{OH})_{3}


Answers (1)

best_answer

\mathrm{NH_4Cl} suppresses the dissociation of \mathrm{NH_4OH} and the concentration of hydroxide ions is less in the solution due to common ion effect. This allows the Group III basic radicals to be precipitated as hydroxides, as the solubility product of Group III hydroxides is lower than Group IV, V and VI  hydroxides.

Thus, only \mathrm{Fe^{3+}} and \mathrm{Al^{3+}} are precipitated as their hydroxides.

Hence, the correct answer is Option (2)

Posted by

Rishi

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