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 $\mathrm{ab}=\left[\mathrm{Fe}^{3+}\right]$ and volume $\mathrm{cd}=\left[\mathrm{Cu}^{2+}\right]$
(b)Volume $\mathrm{ab}=\left[\mathrm{Cu}^{2+}\right]$ and volume $\mathrm{cd}=\left[\mathrm{Fe}^{3+}\right]$
(c)Volume $\mathrm{ab}=\left[\mathrm{Fe}^{3+}\right]$ and volume $\mathrm{ab}=$ excess EDTA
(d)Volume $\mathrm{ab}=\left[\mathrm{Cu}^{2+}\right]$ and volume $\mathrm{cd}=$ 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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