Question

The Cr 3+ ion forms octahedral complexes with three neutral ligands X, Y, and Z. The color of CrX 6 3+ is blue; the color of CrY 6 3+ is yellow; the color of CrZ 6 3+ is red. Which statement is false?
A. Y is the strongest field ligand.
B. CrX63+ ion absorbs the light with the longest wavelength.
C. X is the weakest field ligand.
D. CrZ63+ ion absorbs the light with the shortest wavelength.
E. No answer because all the above statements are true.

Answer 1

Answer:The statement which is false is d

Explanation:

The color which we  see from our eyes is basically the complementary color of wavelength of light which is absorbed.

The wavelegth of light follows the following sequence:

Violet<Indigo<Blue<Green<Yellow<Orange<Red.

So the shortest wavelegth is of violet light and longest wavelength of light is Red.

Since energy is E=hv=hc/λ ;So energy is inversely related with wavelegth and hence

For ligand X the complex has blue color and so we can ascertain that ligand X would have absorbed the Red light as the complementary color of blue light is Red.So the complex of ligand X absorbs the longest wavelegth and hence  the energy gap between the two split d-orbitals t2g and eg  would be very less. Larger the energy gap between t2g and eg orbitals more stronger is the ligand .

So X would be a weak field ligand.

For ligand Y the complex has yellow color and so we can ascertain that ligand Y would have absorbed the Violet  light as the complementary color of yellow light is  violet. Violet has the lowest wavelegth and hence  the energy gap between the two split d-orbitals t2g and eg  would be very large. Larger the energy gap between t2g and eg orbitals more stronger is the ligand .

So Y is a strong field ligand.

For ligand Z the complex has red color and so we can ascertain that ligand Z would have absorbed the blue  light as the complementary color of red light is  blue.The wavelegth of  blue light lies between  violet and red hence  the energy gap between the two split d-orbitals t2g and eg  would be  in between than the other two liagnds.

So Z would be moderate field ligand.

options A , B and C are correct statements.

option D is incorrect because Z absorbs the moderate wavelegth.

The answer is d as it is only statement which is incorrect.