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Question #44595

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The Question

An aqueous solution of bis(glycinato)copper(II), $[Cu(gly)_2]$ , is maintained at 298 K and pH = 8.0 (Solution X). The wavelength of maximum absorption for its $d-d$ transition is $\lambda_X$ , and its spin-only magnetic moment is $\mu_X$ . Aqueous $HClO_4$ is added to Solution X until the pH reaches 1.0, forming Solution Y. The new wavelength of maximum absorption is $\lambda_Y$ , and the magnetic moment is $\mu_Y$ . Given the $pK_a$ values of glycine are 2.34 and 9.60, which of the following represents the correct relationship between the optical and magnetic properties of the two solutions, and identifies the primary copper complex present in Solution Y?

Options

A.
$\lambda_Y > \lambda_X$ , $\mu_Y = \mu_X$ , $[Cu(H_2O)_6]^{2+}$
B.
$\lambda_Y < \lambda_X$ , $\mu_Y = \mu_X$ , $[Cu(glyH)_2]^{2+}$
C.
$\lambda_Y > \lambda_X$ , $\mu_Y < \mu_X$ , $[Cu(H_2O)_6]^{2+}$
D.
$\lambda_Y < \lambda_X$ , $\mu_Y > \mu_X$ , $[Cu(glyH_2)_2]^{4+}$

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

Color and d-d Transitions|Amino Acid Zwitterion pH Sensitivity|Crystal Field Splitting (Octahedral)

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of Coordination Chemistry and Amino Acid equilibria.

Students often treat coordination spheres as static and overlook that ligand protonation at low pH destroys the chelate effect.

This forces a transition from a strong-field N,O-chelate to a weak-field aquo-complex, lowering $\Delta_o$ and causing a bathochromic shift.

A secondary trap tests the magnetic moment of $d^9$ systems, which cannot undergo high-spin/low-spin transitions, keeping $\mu$ constant despite the change in ligand field strength.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	Color and d-d Transitions
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free