Question

Please explain! Thank you!!

A metal element (M) forms a hexadentate complex with the ligand ethylenediammine(en). The formula is M(en)3^2+. The metal ion and the ligand do not absorb in the visiblw region of the spectrum but the complex has a peak absorbance at 450 nm. Using a specrophotometer wutg a 1.00 curvette, the following absorbances were meased for various concentrations of the complex and the ligand

[M2+] M
1.0 x 10 -5
2.0 x 10 -5
3.0 x 10 -5
4,0xl0-5
5.0 x 10-5
6.0 x 10 -5
7.0 x 10-5
8.0 x 10-5
[en]M
2.0 x 10-5
6.0 x 10 -5
12.0 x 10-5
14.0 x 10-5
18.0 x 10-5
22.0 x 10 -5
32.0 x 10-5
48.0 x 10-5
Absorbance at 450 nm
0.04
0.12
0.18
0.24
0.36
0.44
0.64
0.96

Calculate the absorbance coefficient for the complex at 450 nm.

What is the absorbance of a solution with [M^2+]= 2.5 *10^-5 M and [en]= 7.0*10^-5

Answer 1

1 mole of M2+ should give 1 M of M(en)3^2+ complex

So plot M2+ (M) concentration on x-axis vs absorbance on y-axis

the equation from the plot will have slope = molar absorptivity = 0.1183 M-1.cm-1

For a solution with [M2+] = 2.5 x 10^-5 M and [en] = 7.0 x 10^-5 M

absorbance = 0.1183 x 2.5 x 10^-5 = 0.16 [not -ve but +ve]

plot given below