The presence of NH_4Cl in the test solution w | vedclass

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(A) In the qualitative analysis of group $III-A$ cations $(Al^{3+}, Fe^{3+}, Cr^{3+})$,$NH_4OH$ is used as a reagent.$NH_4OH$ is a weak base and disso

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Lowering $[OH^{-}]$

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(A) In the qualitative analysis of group $III-A$ cations $(Al^{3+}, Fe^{3+}, Cr^{3+})$,$NH_4OH$ is used as a reagent.$NH_4OH$ is a weak base and dissociates as: $NH_4OH \rightleftharpoons NH_4^+ + OH^-$.When $NH_4Cl$ is added,it provides a high concentration of $NH_4^+$ ions $(NH_4Cl \rightarrow NH_4^+ + Cl^-)$.According to the common ion effect,the increased concentration of $NH_4^+$ ions shifts the equilibrium of $NH_4OH$ dissociation to the left.This suppresses the dissociation of $NH_4OH$,thereby lowering the concentration of $[OH^-]$ ions to a level sufficient only for the precipitation of group $III-A$ hydroxides while preventing the precipitation of group $IV$ cations.

The presence of $NH_4Cl$ in the test solution while precipitating group $III-A$ hydroxides (in qualitative inorganic analysis) helps in:

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