Question

A 0.0000552 M sample of Compound X in a solvent has an absorbance of 0.266 at 528 nm in a 1.000-cm cuvet. The solvent alone has an absorbance of 0.052. What is the molar absorptivity of Compound X? A different sample of Compound X in the same solvent has an absorbance of 0.528 at 528 nm when measured with the same cuvet. What is the concentration of this second sample?

Answer 1

Beer’s Law

A = e*l*C

A = absorbance of sample

e is the molar absorptivity , the typical units are 1/M-cm

l size of cuvette, typically reported in cm

c is the molar concentration, in mol per ltier or M

substitute

now..

correct Absorbance

Areal = 0.266 -0.052 = 0.214

now... substitute in beer law

A = e*l*C

0.214 = e*1*0.0000552

e = 0.214/0.0000552

e = 3876.81 1/(M-cm)

b)

now..

find new concentration, given A = 0.528

Acorrected = 0.528 - 0.052 = 0.476

substitute in beer law

A = e*l*C

0.476 = 3876.81 *1*C

C = 0.476/ 3876.81

C = 0.0001227 M