Colorimetry is a technique used to determine the concentration of many molecules

Question

Colorimetry is a technique used to determine the concentration of many molecules in solution that do not absorb visible light. One example is the detection of glucose in a sample. Glucose itself will not absorb visible light, but forms a blue-green complex when reacted with toluidine in acetic acid. The analytical wavelength for this complex is 635 nm. A student prepares the following Beer's Law plot Use the plot to answer the following questions. 3. Beer's Law Plot af Absorbance vs. Glucose concentration at 635 nm 0 6 0 03 004 0 05 21

Explanation / Answer

From the plot

a) y = mx + c

m = slope = molar absoptivity = 23.75

b) with absorbance for unknown = 0.732

concentration of glucose solution = 0.732/23.75 = 0.031 M

c) moles of glucose in the tablet = 0.031 M x 0.3 L = 0.0093 mols

d) mass of glucose in tablet = 0.0093 mols x 180.156 g/mol = 1.675 g

e) mass % of glucose in tablet = 1.675 x 100/2.500 = 67.00%

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