A student collects over water in a laboratory at a barometric pressure of
CHEMISTRY · Single correct · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A student collects O2 over water in a laboratory at a barometric pressure of 750mmHg. In a second trial, the student repeats the procedure at the same barometric pressure but with the water temperature raised from 20∘C to 30∘C. The volume of gas collected in both trials is identical. How will the calculated mass of dry O2 from the second trial compare with that from the first?
(a) It will be smaller because, at constant pressure and volume, raising the temperature decreases the number of moles according to n=PV/RT.
(b) It will be greater because the decrease in O2 solubility at the higher temperature forces extra oxygen out of the water and into the collected gas.
(c) It will be smaller because a larger fraction of the total pressure is due to water vapor at 30∘C.
(d) It will be unchanged because the barometric pressure is the same in both trials, so the amount of oxygen collected must be the same.