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Question #44757

Difficulty: 8/10 | 🟢 Free

The Question

A concentration cell is constructed at 298 K as follows:

\ce{Pt(s) | H2(g, 1 bar) | Glycine (aq, 0.1 M) || Gly.HCl (aq, 0.1 M) | H2(g, 1 bar) | Pt(s)}

where 'Glycine' represents the neutral amino acid and 'Gly.HCl' represents glycine hydrochloride. Given for Glycine: $pK_{a1} = 2.30$ , $pK_{a2} = 9.60$ . Assume the pH of the 0.1 M Glycine solution is exactly equal to its isoelectric point. Calculate the electromotive force (EMF) of the cell in mV. (Take $\frac{2.303 RT}{F} = 0.060$ V and $\log 2 = 0.30$ )

Options

A.
255 mV
B.
258 mV
C.
297 mV
D.
318 mV

Check Your Answer

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

Concentration Cells|Gibbs Energy and Spontaneity|Amino Acid Zwitterion pH Sensitivity|Degree of Dissociation (Alpha)

Why This Question Is Tricky

Common Mistakes

This problem tests the integration of electrochemistry with ionic equilibrium, specifically focusing on the pH-dependent dissociation of amino acids.

The primary trap is failing to recognize that Gly.HCl is a weak acid with a relatively large $K_{a1}$ , making the standard approximation $[H^+] = \sqrt{K_a C}$ invalid (yielding 258 mV).

A secondary trap is assuming Gly.HCl acts as a strong acid like HCl (yielding 297 mV) or assuming the zwitterion solution is perfectly neutral at pH 7 (yielding 318 mV).

Quick Facts About This Question

Question Information

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