Preparation of four calibration graphs for two species (not food dyes!) that hav
ID: 478282 • Letter: P
Question
Preparation of four calibration graphs for two species (not food dyes!) that have overlapping spectra produces the following set of extinction coefficients. epsilon_A @ lambda_max for A = 7.8 M^-1 cm^-1 epsilon_A @ lambda_max for B = 2.6 M^-1 cm^-1 epsilon_B @ lambda_max for A = 1.5 M cm^-1 epsilon_B @ lambda_max for B = 5.2 M^-1 cm^-1 Analysis of an unknown solution produces absorbance values of: 0 .45 @ lambda_max for B 0.75 @ lambda_max for A What are the molar concentrations of the unknown A and B (Be sure to show all your work; no credit will be given otherwise.)Explanation / Answer
4. absorbance of mixture is sum total of all the component absorbances
let A and B are concentrations of components,
absorbance = molar absorptivity x path length x concentration
path length = 1 cm
using molar absorptivity values from above
So,
at lambda max A
0.75 = 7.8A + 1.5B
at labda max B
0.45 = 2.6A + 5.2B
solving the two equations for A and B,
concentration of A = 0.088 M
concentration of B = 0.042 M