Finding partial pressure with only T, V and ambient P

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Discussion Overview

The discussion revolves around calculating the partial pressure of nitrogen (N2) collected over water at a specific temperature and atmospheric pressure. Participants explore the implications of the ideal gas law and the effects of water vapor pressure on the total pressure in the system.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant presents a homework problem involving the collection of nitrogen gas over water and attempts to apply the ideal gas law to find the partial pressure of N2.
  • Another participant argues that the ideal gas law is irrelevant in this context, suggesting that the key factor is the equilibrium vapor pressure of water at the given temperature.
  • A third participant comments on the potential confusion caused by the inclusion of the volume of gas in the problem, implying it may not be necessary for solving the question.
  • A later reply suggests that extraneous details in problems can serve as a learning tool for students to discern what information is essential.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of the ideal gas law to the problem, indicating a lack of consensus on the best approach to find the partial pressure of nitrogen.

Contextual Notes

Participants note the importance of considering the vapor pressure of water and the potential distractions caused by additional information in the problem statement. There is uncertainty regarding the assumptions made about total pressure and the role of container height.

Felchi
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Homework Statement


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

Homework Equations


PV=nRT
Pt=P1+P2...

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

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.

Pt=P1+P2?

Pt=101.3kPa+PN...Pt is not given...doesn't work.

Cannot assume Pt is ambient pressure because container's height affects pressure.
 
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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
 
And the 60L seems also thrown into confuse you - second question with that feature in a row.
 
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Likes   Reactions: Chestermiller
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 ;)
 

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