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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

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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

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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

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