Gchem

[Lonely Sol]

Advertisement - Members don't see this ad

A sample of air held in a graduated cylinder over water has a volumne of 88.3ml at a temperature of 18.5 degree C. and a pressure of 741nm. What would the volume of the air be if it were dry and at the same temperature and pressure?

 

[Nasem]

This is classic PV = nRT,
Since n, R, and T are constancts in this, we leave them out and put

PiVi = PfVf

You know your initial pressure and volume,
you also know your final pressure (since it says constant), just need to solve for Vf

 

[orthdent786]

if thats the case then Vi=Vf b/c the pressures just cancel out, i'm not sure if that is the equation we are supposed to use? maybe someone else can help?

 

[doc toothache]

A sample of air held in a graduated cylinder over water has a volumne of 88.3ml at a temperature of 18.5 degree C. and a pressure of 741nm. What would the volume of the air be if it were dry and at the same temperature and pressure?

The (vapor) pressure contributed by water at 18.5 degree C is about 20mm. It needs to be subtracted from 741mm then use P1V1=P2V2.

 

[infernobutterfl]

The (vapor) pressure contributed by water at 18.5 degree C is about 20mm. It needs to be subtracted from 741mm then use P1V1=P2V2.

we are supposed to know the vapor pressure of water?? 😵

 

[DentalKitty]

we are supposed to know the vapor pressure of water?? 😵

No, I think it would be provided for you especially since VPs are temp dependent so you'd have to memorize so many. The only one I know is H2O at 100 deg C = 760mm because at the boiling point VP = atmospheric pressure. That would work for any substance at its BP and 1atm I believe.