Question

A mixture solution of Co(II) and Ni(II) shows an absorbance of 0.500 at 500 nm. What percentage of incident light is absorbed by the solution?

Under the given conditions if 20% of the absorbance is ascribed to the contribution of Co(II), what will the absorbance of Ni(II) be?

Answer 1

Given that

Absorbance of the solution = A = 0.500

Absorbance is related intensity of light before and after passing through the medium as follows

Where Io = intensity before passing the solution

I = intensity after passing the solution

Hence, putting in A = 0.500

Intensity of light absorbed by the solution = intensity Incident light - intensity of transmitted light =

Hence, percentage of light absorbed by the solution can be written as

Hence, 68.4 % of the incident light is absorbed by the solution.

It is given that 20% of the total light absorbed is absorbed by Co(II). Hence, 80% of the total light must be absorbed by Ni(II) as they are the only two ions that are absorbing light.

Hence, percentage of total incident light that is absorbed by Ni(II) is

Hence,

Hence, the absorbance of Ni(II) in the solution will be 0.344.