Q19 · CSIR-NET Chemistry, June 2019

Paper: CSIR-NET June 2019 · Subject: Inorganic Chemistry · Chapter: Analytical Chemistry · Topic: Analytical Chemistry – General · Marks: 2 · Difficulty: Medium

The role of $\mathrm{H}_{3} \mathrm{PO}_{4}$ in the estimation of Fe (II) with $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ using diphenylamine sulphonate as ndicator is to
(a)avoid aerial oxidation of Fe(II)
(b)reduce the electrode potential of $mathrm{Fe^{3+} ext{-}Fe^{3+}}$
(c)stabilize the indicator
(d)stabilize $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Phosphate complexes Fe³⁺ and lowers the Fe³⁺/Fe²⁺ potential, sharpening the end point (b).

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