Final answer:
The measured molar volume will be too low if oxygen dissolves in the water and is not accounted for. Henry's law can be used to calculate the correction needed for the solubility of oxygen at different partial pressures.
Step-by-step explanation:
When oxygen gas dissolves in water in an experiment where gas is collected over water, the measured molar volume of the gas will be affected. If the volume of the gas is not corrected for the dissolved oxygen, the calculated molar volume will be too low. This is because some of the oxygen gas that would otherwise occupy space above the water is now dissolved in the water, thus reducing the volume of gas collected.
Henry's law provides a relationship between the solubility of a gas in a liquid and the partial pressure of the gas above the liquid. Using Henry's law, the solubility of oxygen when its partial pressure is reduced can be determined. For example, the concentration of dissolved oxygen in water at 20.7 kPa can be found by applying the Henry's law constant obtained at the standard conditions of 101.3 kPa.
In practical terms, if the experiment is conducted and the volume of gas collected is known without accounting for the oxygen dissolved in water, applying a correction factor that accounts for the solubility of oxygen, as calculated using Henry's law, could provide a more accurate measure of the molar volume of the gas.