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JEE Mains · Chemistry · STD 12 - p -Block elements - ll

In the precipitation of the iron group (III) in qualitative analysis, ammonium chloride is added before adding ammonium hydroxide to :

  1. A increase concentration of \(Cl ^{-}\)ions
  2. B increase concentration of \(NH _4{ }^{+}\)ions
  3. C prevent interference by phosphate ions
  4. D decrease concentration of \({ }^{-} OH\) ions
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Correct Answer

(D) decrease concentration of \({ }^{-} OH\) ions

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\(NH _4 OH \rightleftharpoons NH _4^{+}+ OH ^{-}\) \(NH _4 Cl \rightarrow NH _4^{+}+ Cl\) Due to common ion effect of \(NH _4^{+}\), [ \(OH ^{-}\)] decreases in such extent that only group-III cation can be precipitated, due to their very low \(K_{s p}\) in the range of…
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