Measuring the Henry's Law Constant for Carbon Dioxide and Water with UV-visible Absorption Spectroscopy

The Henry's law constant defines the solubility of a gas in a liquid solution. In this study, a new method for measuring the Henry's law constant is described. This new colorimetric method is suited for gases which react with water to form acidic or basic solutions when they dissolve, and makes use of measuring the concentration of two forms of a colorimetric pH indicator. By measuring the concentration of the protonated and deprotonated forms of the indicator with UV-visible absorption spectroscopy, the concentration of the hydronium in solution was determined. After determining the hydronium concentration, the equilibrium expression for the dissolved gas reacting with water was solved to determine the concentration of the dissolved gas. The concentration of the dissolved gas and the measured partial pressure of the dissolved gas at equilibrium were then used to calculate the Henry's law constant for the gas. The efficacy of the method is demonstrated by measuring the Henry's law constant for carbon dioxide in water over a range of pressures (0.680 - 5.10 atm). The results obtained with this method are comparable to the value for the Henry's law constant that have been previously reported via more traditional methods, and yielded values for the Henry's law constant for carbon dioxide that ranged from 3.45 × 10^-2 to 3.99 × 10^-2 M atm^-1.