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To avoid the precipitation of hydroxides...

To avoid the precipitation of hydroxides of `Ni^(2+),Co^(2+),Zn^(2+) and Mn^(2+)` along with those of `Fe^(3+),Al^(3+) and Cr^(3+)` the third group cations, solution should be:

A

Heated with few drops of concentrated `HNO_3`

B

Boiled with excess of ammonium chloride

C

Concentrated to small volume

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
B
Function of strong electrolyte `NH_4Cl` is to suppress the ionisation of `NH_4OH` so that the concentration of `OH^-` ions in the solution is decreased but it is sufficient to precipitate the third group basic radicals because the solubility prouduct of group III hydrooxides is lower than IV, V and VI group hydroxides. The `Cr(OH)_3darr` is slightly soluble in excess of precipitant , upon boiling the solution, `Cr(OH)_3` is precipitated.
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