The teacher gave another student a 0.10 M solution of an unknown indicator solution. The wavelength of maximum absorbance is 640 nm, the molar mass of the unknown indicator was 347 g mol-1, and the density of the solution was 1.00 g mL-1 . To facilitate the construction of the calibration curve, the student used a standard cuvette as the reference in the spectrophotometer and placed the various dilutions in a series of test tubes. The resulting calibration curve seemed very erratic. What was the student’s error?

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