Finding partial pressure with only T, V and ambient P

[Felchi]

Homework Statement

60 L of N₂ are collected over H2O at 40^oC when atmospheric pressure is 760.00 torr. What is partial pressure of N₂?

Homework Equations

PV=nRT
P_t=P₁+P₂...

Vapor pressure of H₂O at 40^oC:7.3590 KPa
760 torr=101.3 kPa
40^oC=313^oK

The Attempt at a Solution

PV-nRT
(60)101.3=313(n)8.3145
((60)101.3)/((313)8.3145)=2.166g...That doesn't help, mass of H₂O unknown.

P_t=P₁+P₂?

P_t=101.3kPa+P_N...P_t is not given...doesn't work.

Cannot assume P_t is ambient pressure because container's height affects pressure.

 

[Chestermiller]

This has nothing to do with the ideal gas law. That's just a "red herring" that they threw into confuse you. The nitrogen has been bubbled through water, so the bubbles have come to the equilibrium vapor pressure of water at the temperature of the liquid. If the partial pressure of the water is its equilibrium vapor pressure and the total pressure is 760 mm Hg, what is the partial pressure of the nitrogen?

Chet

 

[epenguin]

And the 60L seems also thrown into confuse you - second question with that feature in a row.

 

[Borek]

Let's face it - in the real world we are distracted by so many things, it is quite a good idea to add unnecessary information to problems just to make students learn what and when to ignore ;)