An environmental laboratory is determining nitrate concentration in groundwater by…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
An environmental laboratory is determining nitrate concentration in groundwater by converting the nitrate to a colored species. For a particular groundwater sample the laboratory has already established that the molar absorptivity at the chosen wavelength is 3.75×103Lmol−1cm−1. Three quartz cells are available: a standard 1.00 cm cell, a short-path 0.25 cm cell, and a long-path 5.00 cm cell. The analyst estimates the nitrate concentration in the sample to be 1.8×10−5molL−1. Answer the following questions about selecting an appropriate cell.
(a) Calculate the expected absorbance for the sample in each of the three cells listed above. Show your work with proper units.
(b) Identify which cell, if any, will yield an absorbance that falls within the recommended range of 0.10 – 1.00. Justify your choice based on the calculations in part (a).
(c) If none of the cells produces an absorbance in the recommended range, state what additional sample handling step(s) could be taken to bring the measured absorbance into the optimal range, and explain the chemical reasoning behind your suggestion.