What does water saturated oxygen mean in this question:

The vapour pressure of water at 80º C is 355 torr. A 100 ml vessel contained water saturated oxygen at 80º C, the total gas pressure being 760 torr. The contents of the vessel were pumped into a 50.0 ml, vessel at the same temperature. What were the partial pressures of oxygen and of water vapour, what was the total pressure in the final equilibrated state ? Neglect the volume of any water which might condense

  • $\begingroup$ Oxygen saturated by water vapor, similarly as air saturated by water vapor, i.e. having 100% relative humidity. $\endgroup$
    – Poutnik
    Commented Jul 4, 2021 at 4:59
  • $\begingroup$ Does that mean the water(l) and water(g) are in equilibrium? $\endgroup$
    – Prabodh
    Commented Jul 4, 2021 at 8:42
  • $\begingroup$ Yes, if water(l) is present. It need not to be. $\endgroup$
    – Poutnik
    Commented Jul 4, 2021 at 10:25
  • $\begingroup$ Please, Prabodh ! Try to start some beginning of calculation. The Forum will never do all the job, and you nothing. We are here to help those who try to solve their homework and are stopped by a difficulty. We will help them. So go ahead, start some trials. Tell us where you are stopped. We will help you. $\endgroup$
    – Maurice
    Commented Jul 4, 2021 at 19:56
  • $\begingroup$ @Maurice In my understanding, the OP have not asked us to solve the task, but to explain the expression, providing the task as the expression context. $\endgroup$
    – Poutnik
    Commented Jul 5, 2021 at 7:15

1 Answer 1


Consider the partial pressures separately. If you answer these questions you have your own solution.

Oxygen does not condense, may be deemed an ideal gas. What does halving the volume do to its partial pressure? (We assume that exactly half the volume, 50 ml vs 100 ml, is available because we neglect the liquid volume in this problem.)

Water can condense, adjusting its partial pressure back down to equilibrium. What would that restored equilibrium pressure be versus the vapor pressure given in the problem?

Finally, what does not condense is still essentially an ideal gas, add the partial pressures to get the total pressure.

Good luck!


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