Student Doctor Network Forums Raoult's Law , vapor pressure lowering?
 Register FAQ SDN Live Mark Forums Read

 MCAT Study Question Q&A Subforum specifically for asking questions when studying for the MCAT. Please no actual MCAT questions. RSS:

 05-08-2012, 10:54 PM #1 Senior Member   Join Date: Mar 2011 Posts: 166 Raoult's Law , vapor pressure lowering? SDN Members don't see this ad. (About Ads) How does Raoult's law apply to solids dissolved in liquids. like NaCl dissolved in water how would we be able to determine how much did the vapor pressure decrease in our solution? Usually if we have two liquids we can use each of the individual pressures of the liquids and multiply by Molar percentage and then add each partial pressure to get the vapor pressure for all the solution Do solids have a vapor pressure in order for us to use that equation?
05-08-2012, 11:15 PM   #2
1K Member

Status: Pre-Medical
Join Date: Jan 2012
Posts: 1,479

I would think it does apply to small amounts of dissolved solids. Not sure though, Kaplan only says:

Quote:
 Raoult's law holds only when the attraction between the molecules of the different components of the mixture = the attraction b/w the molecules of any one component in its pure state.
The NaOH bond and the NaCl bonds are both ionic bonds, so they are equal strength attractions.

Quote:
 In any real solution of, say, a salt in water, there are strong attractions between the water molecules and the ions. That would tend to slow down the loss of water molecules from the surface. However, if the solution is sufficiently dilute, there will be good-sized regions on the surface where you still have water molecules on their own. The solution will then approach ideal behaviour.
http://www.chemguide.co.uk/physical/...ultnonvol.html

Last edited by SaintJude; 05-08-2012 at 11:30 PM.

 05-09-2012, 10:02 AM #3 Senior Member   Join Date: Mar 2011 Posts: 166 Oh i got it .. Thanks for the link made it clear So to calculate the change in vapor pressure we just use the molar percentage of solute * pure vapor pressure of solvent Then we subtract it from pure vapor pressure Excellent !!

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules