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Question #44780

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The Question

A copper electrode is immersed in a buffer solution at $298\text{ K}$ with a $\text{pH} = 8.0$ . The solution contains a total analytical concentration of glycine ( $\ce{H2NCH2COOH}$ ) equal to $0.11\text{ M}$ and total copper(II) ions equal to $1.0 \times 10^{-3}\text{ M}$ .

Given: $E^\circ_{\ce{Cu^{2+}/Cu}} = +0.34\text{ V}$ $\frac{2.303 RT}{F} = 0.06\text{ V}$ $pK_{a1} = 2.0$ , $pK_{a2} = 9.0$ for glycine. The overall formation constant for the bis(glycinato)copper(II) complex, $[\ce{Cu(Gly)2}]$ , is $\beta_2 = 10^{16}$ .

Assuming that complexation does not significantly alter the pH or the total ligand concentration, what is the reduction potential of the copper electrode?

Options

A.
-0.11 V
B.
-0.17 V
C.
+0.25 V
D.
-0.05 V

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Electrode Potential Dependencies|Amino Acid Zwitterion pH Sensitivity

Why This Question Is Tricky

Common Mistakes

This problem tests the integration of electrochemistry with complexometric equilibria and pH-dependent speciation.

The 'hidden variable' is the actual concentration of the active ligand (glycinate anion).

Students often fall into the trap of using the total analytical concentration of the amino acid ( $0.11\text{ M}$ ) as the ligand concentration, ignoring that at $\text{pH} = 8.0$ , the amino acid exists predominantly as a non-coordinating zwitterion.

Failing to apply the Henderson-Hasselbalch equation to find the true $[\ce{L-}]$ leads to an incorrect $Q$ -value in the Nernst equation, drastically shifting the calculated electrode potential (leading to Distractor B).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Electrochemistry - Class 12
Concept	Electrode Potential Dependencies
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free