## Module 3B Calculating the molar absorbance coefficient from some data.

1

Given the data below, calculate the molar absorbance coefficient. The width of the cuvette was 1 cm.

 Concentration (mM) Absorbance 2 0.16 5 0.39 10 0.78 15 1.16 20 1.54

epsilon = mM-1.cm-1 = M-1.cm-1 express your answer to one significant figure.

well done

incorrect

choose two points on the line (10, 0.078) (20, 1.54)

slope = (1.54-0.078) / (20-10)

= 0.76 / 10

= 0.08 mM-1

the pathlength was 1cm so epsilon = 0.08 mM-1.cm-1 = 80 M-1.cm-1

2

Given the data below, calculate the molar absorbance coefficient. The width of the cuvette was 1 cm.

 Concentration (μM) Absorbance 2 0.12 4 0.25 6 0.35 8 0.49 10 0.59

epsilon = μM-1.cm-1 = M-1.cm-1 express your answer to one significant figure.

well done

incorrect

choose two points on the line (10, 0.078) (20, 1.54)

slope = (0.59-0.12) / (10-2)

= 0.47 / 8

= 0.06 μM-1

the pathlength was 1cm so epsilon = 0.06 μM-1.cm-1 = 60000 M-1.cm-1

3

Given the data below, calculate the molar absorbance coefficient. The width of the cuvette was 1 cm.

 Concentration (μg/L) Absorbance 10 0.039 20 0.077 40 0.157 80 0.310 150 0.586

epsilon = μg-1.L.cm-1 = M-1.L.cm-1 express your answer to one significant figure.

well done

incorrect

choose two points on the line (10, 0.039) (20, 0.077)

slope = (0.077-0.039) / (20-10)

= 0.038 / 10

= 0.04 μg-1.L

the pathlength was 1cm so epsilon = 0.04 μg-1.L.cm-1 = 4000 g-1.L.cm-1