CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
To characterize compound Q, a student prepares a single standard solution that is 1.00 × 10⁻⁴ M in Q. Using a cuvette whose internal path length is 1.20 cm, the standard displays an absorbance of 1.15 at a chosen wavelength.
The same cuvette is then rinsed and filled with an unknown solution of Q. The instrument reports an absorbance of 0.672 for the unknown.
Respond to the following prompts.
(a) Determine the molar absorptivity of compound Q at this wavelength based on the single standard measurement.
(b) Calculate the concentration of Q in the unknown solution.
(c) The spectrophotometer’s absorbance readings carry an uncertainty of ±0.005. Assuming the path length and molar absorptivity are exact, estimate the absolute uncertainty (±) in the concentration obtained in part (b). Use proper propagation of uncertainty and express the result with an appropriate number of significant figures.