A group of students is constructing a calibration curve to determine the…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A group of students is constructing a calibration curve to determine the concentration of the red–orange complex FeSCN2+ produced in an equilibrium mixture. They prepare five standard solutions ranging from 0.00 mM to 0.80 mM FeSCN2+ and measure their absorbances in a 1.00 cm cuvette at the wavelength of maximum absorbance for the complex. Before collecting data, the students run a blank containing all reagents except Fe(III) and SCN− so that the final concentration of FeSCN2+ is effectively zero.
(a) Describe the specific purpose of recording the absorbance of the blank before measuring the standards.
(b) Explain why selecting the wavelength of maximum absorbance for FeSCN2+ increases the sensitivity of the calibration curve.
(c) Identify and justify two considerations the students should use when choosing the numerical scale for the absorbance and concentration axes so that the slope of the best-fit line can be determined with minimal uncertainty.