Q25 · CSIR NET Chemistry, June 2012
Paper: CSIR NET June 2012 · Subject: Inorganic Chemistry · Chapter: Analytical Chemistry · Topic: Analytical Chemistry – General · Marks: 2 · Difficulty: Medium
The spectrophotometric response for the titration of a mixture of $\mathrm{Fe^{3+}}$ and $\mathrm{Cu^{2+}}$ ions against EDTA is given below. 
The correct statment is:
The correct statment is:(a)Volume ab = $[\mathrm{Fe^{3+}}]$ and volume cd = $[\mathrm{Cu^{2+}}]$
(b)Volume ab = $[\mathrm{Cu^{2+}}]$ and volume cd = $[\mathrm{Fe^{3+}}]$
(c)Volume ab = $[\mathrm{Fe^{3+}}]$ and volume ab = excess EDTA
(d)Volume ab = $[\mathrm{Cu^{2+}}]$ and volume cd = excess EDTA
Answer
Answer: C ✓ checked by 4AB · confidence low
Explanation
Fe³⁺ (log K_FeY ≈ 25) is titrated first, along the flat segment ab. CuY (blue) then raises the absorbance from b to c, and cd is excess EDTA. The options are garbled; the chapter key gives (c).
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