Question

Correct increasing order for the wavelengths of absorption in the visible region the complexes of $C{o}^{3+}$ is :

• A. $[Co(H_{2}O{)}_6{]}^{3+},[Co(en{)}_3{]}^{3+},[Co(N{H}_3{)}_6{]}^{3+}$
• B. $[Co(H_{2}O{)}_6{]}^{3+},[Co(N{H}_3{)}_6{]}^{3+},[Co(en{)}_3{]}^{3+}$
• C. $[Co(N{H}_3{)}_6{]}^{3+},[Co(en{)}_3{]}^{3+},[Co(H_{2}O{)}_6{]}^{3+}$
• D. $[Co(en{)}_3{]}^{3+},[Co(N{H}_3{)}_6{]}^{3+},[Co(H_{2}O{)}_6{]}^{3+}$

Answer 1

Answer: (D)

The order of the ligand in the spectrochemical series

$H_{2}O<N{H}_3<en$

Hence, the wavelength of the light observed will be in the order

${\left[Co{\left(H_{2}O\right)}_6\right]}^{3+}<{\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}<{\left[Co(en{)}_3\right]}^{3+}$

Thus, wavelength absorbed will be in the opposite order

i.e., ${\left[Co(en{)}_3\right]}^{3+},{\left[Co{\left(N{H}_3\right)}_6\right]}^{3+},{\left[Co{\left(H_{2}O\right)}_6\right]}^{3+}$