The protein metmyoglobin and imidazole form a complex in solution. The molar ext

Question

The protein metmyoglobin and imidazole form a complex in solution. The molar extinction coefficient for metmyoglobin is 0.942L/mol cm at 500 nm . The molar extinction coefficient for complex is 0.688L/mol cm at 500nm Equilibrium is established in a solution which has an initial concentration of metmyglobin equal to a 0.59M. The soluton reaches equilibrium and demonstrates an absorbance of 0.435 at 500 nm.

Assuming the reaction is metmyglobin ----------> complex

What is the value of K, the equilibrium constant for the reaction?

Explanation / Answer

First we have to find the concentration of complex at equilibrium:

Given that absorbance A = 0.435

lenth of cuvette l = 1cm

molar extinction coefficient for complex, e = 0.688 L/(mol.cm)

concentration of complex , c = ?

From Beer's law,

A = ecl

c = A / el

= (0.435)/ ( 0.688 L/(mol.cm) ) (1cm)

= 0.632 M

c = 0.632 M

Therefore, concentration of complex = 0.632 M

calculation of  K, the equilibrium constant for the reaction:

metmyglobin ----------> complex

concentration of complex at equilibrium = 0.632 M

concentration of metmyglobin = 0.59 M

K= 0.632/0.59 =1.07

K = 1.07

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