In an experiment as described in the Principles section, 158 mL of O2 is collected over water. The mass of the O2 is measured to be 0.207 g, the temperature is 290 K and the barometric pressure that day is 754 mm Hg. Calculate the value of R in the units L, atm, K, mol. Remember: The pressure measured is the pressure of a mixture of water vapor and the gas we are interested in, O2. To correctly calculate the partial pressure of O2, the vapor pressure of the water must be accounted for.