A research team is studying the green pigment malachite green at 617 nm
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A research team is studying the green pigment malachite green at 617 nm. Using a 1.20 cm quartz cuvette, they prepare six standard solutions and obtain the data shown.
Concentration (mol L⁻¹)
Absorbance
0.00500
0.159
0.0100
0.316
0.0150
0.473
0.0200
0.623
0.0250
0.783
0.0300
0.939
(a) Construct a well-labeled sketch (no numerical plotting required) of absorbance versus concentration. On your sketch, indicate the expected shape of the best-fit line.
(b) Using the first and last data points, calculate the slope of the line. Show your work and include units.
(c) From your calculated slope, determine the molar absorptivity of malachite green at 617 nm.
(d) An unknown sample measured in the same cuvette shows an absorbance of 0.512. Estimate its concentration using your calibration results.
(e) Discuss one potential source of systematic error that could cause the y-intercept of an experimental calibration line to deviate from zero, and explain how this would affect the determination of unknown concentrations.