determine the vapor pressure of a solution at 55 degrees C that contains 34.2g NaCl in 375 mL of water. The vapor pressure of pure water at 55 degrees C is 118.1 torr.

Question

so Psolution=XsolventPsolvent

I don't know why I'm not getting the correct answer...

so from 34.2g NaCl you find the moles which is .585216 moles

then from 375mL of water you find the moles which is 20.810211 moles

so isn't it 20.810211/20.810211+.585216

then multiply this with 118.1 torr

...the answers supposed to be 112 torr, im getting like 114

Answer 1

One item easily overlooked is that the density of water at 55 degrees C may not be 1.00. I looked it up and if the value I obtained is correct, it is about 0.9857 which makes the mass of the water more like 370 g BUT that didn't change the final answer much. I don't see anything wrong with your calculation. If you find out we did something wrong please post something to let us know what.

Answer 2

you have to multiply by the van't hofft factor of nacl to the solute, and if you do so and divide by the total you will get 112 torr

Answer 3

NaCl i=2
so when you calculate Xh2o you need to tmes nacl moles with 2 then find the mole fraction

Answer 4

thanks