A research team is developing a protocol for measuring the concentration of a dye in…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A research team is developing a protocol for measuring the concentration of a dye in river water samples. The instrument available in the field does not allow the user to change the wavelength, but it does allow the choice of several glass cells with path lengths of 0.5 cm, 1.0 cm, and 4.0 cm.
The manufacturer of the instrument recommends that measured absorbance values fall between 0.10 and 1.00 to minimize relative error due to instrumental noise and stray light.
Answer the following questions about how path length influences data quality when analyzing the river water samples.
(a) Describe qualitatively how changing only the path length while keeping all other variables constant will affect the measured absorbance of a sample.
(b) Explain why measurements that give absorbance values much lower than 0.10 or much higher than 1.00 are less reliable, making explicit reference to the role of instrumental limitations.
(c) If preliminary testing shows that the dye concentration in the river water varies widely from site to site, explain how selecting among the three available path lengths can help the team keep all measurements within the recommended absorbance range without diluting or concentrating the samples.