The molar absorptivity (with units L mol⁻¹ cm⁻¹) of an organic dye Y was measured at…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
The molar absorptivity (with units L mol⁻¹ cm⁻¹) of an organic dye Y was measured at three different wavelengths; the results are tabulated below.
Wavelength (nm) ε (×10⁴)
420 4.1
450 5.2
500 1.8
A solution of dye Y, whose concentration is expected to be approximately 6.0 × 10⁻⁶ mol L⁻¹, is to be analyzed in a 1.00 cm path-length cuvette.
Answer the following.
(a) Decide which of the three listed wavelengths should be used to obtain the calibration curve for dye Y. Support your choice with a quantitative comparison based on the data provided.
(b) Using the wavelength chosen in part (a), calculate the absorbance that would be observed for a 6.0 × 10⁻⁶ mol L⁻¹ solution of dye Y.
(c) The spectrophotometer can reliably detect a change in absorbance as small as 0.005. At the wavelength selected in part (a), determine the minimum change in concentration of dye Y (in mol L⁻¹) that can be distinguished by this instrument.