1.

What will be the correct order for the wavelengths of absorption in the visible region for the following: [Ni(NO_(2))_(6)]^(4-), [Ni(NH_(3))_(6)]^(2+), [Ni(H_(2)O)_(6)]^(2+)

Answer»

Solution :As metal ion is fixed, the WAVELENGTH of absorption will be decided by the field STRENGTHS (CFSE values) of the ligands.
From the spectrochemical series, the order of CFSE is :`H_(2)OltNH_(3)ltNO_(2)^(-)`
Thus, the ENERGIES absorbed for excitation will be in the order :
`[Ni(H_(2)O)_(6)]^(2+)lt[Ni(NH_(3))_(6)]^(2+)lt[Ni(NO_(2))_(6)]^(4-)`
As wavelength and energy are inversely related `(E=(hc)/(lamda))`
The wavelengths absorbed will be in the OPPOSITE order :
i.e., `[Ni(H_(2)O)_(6)]^(2+)gt[Ni(NH_(3))_(6)]^(2+)gt[Ni(NO_(2))_(6)]^(4-)`


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