# Homework Help: I need help on a chemistry problem PLEASEEE

1. Feb 24, 2006

### jKotha

Ok, I need to calculate the vapor pressure of water.

All the information I am given is that the temp is 43.0 C, and I know the total pressure of the system is 758.3 torr.

Is there anyway I can calculate this using the Pwater = Ptotal - Pair equation? PLEASE HELP!! Thanks guys

Jkotha

2. Feb 25, 2006

### biochemist

Is it something related to the equation for ideal gas? but in pV = nRT, the "n" has changed cos in 43.0 C water is liq but vapor is gas. Sorry, i've got no idea about it since I'm doing biology...

3. Feb 25, 2006

### GCT

first things first, state the full problem.

4. Feb 25, 2006

### jKotha

Full Problem

um.. that is the full problem. PV=NRT gives me the total pressure. I just need to find the vapor pressure of water.

This is what the problem says.
Consider the following data:
Temp = 43.0C Volume = 6.63ml
Barometric Pressure = 758.3 torr

a. Find the moles of air trapped in the cylinder

Ok, I can do this part by solving for n, in the ideal gas law. This is not a problem... the second part is the problem.

b. Calculate the vapor pressure of water, Pwater, at 43.0C

THIS IS THE FULL PROBLEM. Now I would really appreciate it if you can help. Thanks Guys..

jkotha

5. Feb 26, 2006

### Plastic Photon

Assume that the total pressure is 760 torr and 758.3 as the partial pressure of the gas.

6. Feb 27, 2006

### jKotha

Thanks.. that might help

would that mean that the vapor pressure of the water would be 1.7 torr? That seems incredibly low. I'm assuming that total pressure = Pressure(gas) + pressure(water)

760 = 758.3 + Pwater

.. this doesnt seem right. That is really low.

hm... I don't know why this is so tough.

thanks

jkotha

7. Feb 27, 2006

### Plastic Photon

It is not that unusual, water is a liquid and so the particles are not moving around as much as they are in its gaseous state of steam.