A Simple Pressure-Based Method for the Determination of Henry’s Law Constant of CO2 in Water by Addition of a Known Mass of CO2(s)

The Henry’s law constant (k) is determined by adding a known mass of CO2(s) to a known volume of water in a Schlenk flask and measuring the total gas pressure. The partial pressure of CO2(g) is equal to the measured pressure minus the atmospheric pressure, an application of Dalton’s law. Having determined the partial pressure of CO2(g), the moles of CO2(g) are calculated using the ideal gas law. With moles of CO2(g) known, the moles of CO2(aq) are calculated and used to determine the concentration of CO2(aq). From these, the Henry’s law constant is calculated. This is a simple and straightforward method to determine the Henry’s law constant of CO2 in water. Students report k values of 0.0318 ± 0.004 mol/(L.atm) (N = 20), which compares favorably with literature values. In order to increase the pedagogical value of this laboratory exercise, the pressure that is expected for a given set of experimental values (mass of CO2(s), volume of Schlenk flask, volume of water, temperature, atmospheric pressure, Henry’s law constant) is predicted prior to experimentation. The mathematical manipulation that is required is well within the reach and understanding of general chemistry students.