Question

Correct increasing order for the wavelengths of absorption in the visible region by the complexes of `Co^(3+)` is:
A. `[Co(H_(2)O)_(6)]^(3+) , [Co(en)_(3)]^(3+) , [Co(NH_(3))_(6)]^(3+)`
B. `[Co(H_(2)O)_(6)]^(3+) , [Co(NH_(3))_(6)]^(3+) , [Co(en)_(3)]^(3+)`
C. `[Co(NH_(3))_(6)]^(3+) , [Co(en)_(3)]^(3+) , [Co(H_(2)O)_(6)]^(3+)`
D. `[Co(en)_(3)]^(3+) , [Co(NH_(3))_(6)]^(3+) , [Co(H_(2)O)_(6)]^(3+)` .

Answer 1

Correct Answer - D
d) In increasing order, crystal field splitting energy for the neutral ligands involved in:
`H_(2)Olt NH_(3) lt en`.
Thus, the increasing order of energy for the given complexes is:
`[Co(H_(2)O_(6))]^(3+) lt [Co(NH_(3))_(6)]^(3+) lt [Co(en)_(3)]^(3+)`
Since, E = `(hc)/(lambda)` i.e., `=(Ealpha) 1//lambda`
The increasing order of wavelength of absorption is the reverse.
`[Co(en)_(3)]^(3+) lt [Co(NH_(3))_(6)]^(3+) lt [Co(H_(2)O)_(6)]^(3+)`