A student obtains a calibration graph of versus for a known dye and observes a…
CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A student obtains a calibration graph of A versus c for a known dye and observes a positive y-intercept of 0.05 absorbance units even though the cuvette was reported to be clean. Which of the following explanations is most consistent with this nonzero intercept?
(a) Random instrumental noise that increases proportionally with concentration artificially shifts the calibration line upward.
(b) Deviation from the Beer–Lambert law at higher concentrations produces curvature whose best-fit line intersects the y-axis above zero.
(c) Residual absorbance by the solvent or cuvette contributes a constant background signal.
(d) The molar absorptivity of the dye decreases at very low concentrations, so extrapolation of the calibration line gives a positive intercept.