Finding the Rate

Question

A student completed a similar lab experiment and got an ε_avg of 78 M^-1cm^-1. If their change in absorbance (∆A) for the first 1.5 minutes was 0.559 and the cuvette was 1.0 cm wide, what was the rate for the first 1.5 minutes? 

Answer 1

Beer Lambert Law: A = ecl

A = absorbance = 0.559

e = extinction coefficient = 78 M-1cm-1

c = concentration in M = ?

l = path length in cm = 1.0 cm

Solve for c (concentration)

c = A / el = 0.559 / 78 x 1 = 0.00717 M

This is the change in concentration over 1 period of 1.5 minutes.

The rate can thus be expressed as 0.00717 M / 1.5 min = 0.00478 M / min