Raoult’s Law Comparison of Liquid Mixtures Using UV–vis Spectroscopy: A Physical Chemistry Laboratory Experiment

An undergraduate physical chemistry experiment is described in which two different liquid mixtures are investigated through UV–vis spectroscopy to quantify which mixture behaves more ideally. Students create liquid mixtures of specified mole fractions and then measure the relative vapor pressure of each compound in the head space above the mixture using UV–vis spectroscopy. By creating Raoult’s law plots and fitting the total vapor pressure to a second-order polynomial, students are able to quantitatively determine that the acetone/toluene mixture exhibits a higher deviation from ideal behavior when compared to the acetone/ethyl acetate mixture. Strategies for minimizing error are outlined which help to ensure consistent experimental results.