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

Options

  1. Aincrease concentration of ( Cl ⁻ )ions
  2. Bincrease concentration of ( NH ₄ ⁺ )ions
  3. Cprevent interference by phosphate ions
  4. Ddecrease concentration of ( ⁻ OH ) ions

Correct answer

D. decrease concentration of ( ⁻ OH ) ions

Step-by-step solution

aligned & NH ₄ OH NH ₄⁺+ OH ⁻ & NH ₄ Cl NH ₄⁺+ Cl aligned 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 _ sp in the range of 10⁻³⁸ .

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