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.

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

NaCl i=2

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

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.

thanks

It seems like you're on the right track, but there might be a calculation error in your approach. Let's break it down step by step to ensure we're following the correct calculations.

First, we need to find the mole fraction of the solvent (water) in the solution. The mole fraction is calculated by dividing the number of moles of the solvent by the total number of moles of all components in the solution.

You correctly found the moles of NaCl to be 0.585216 moles. However, the moles of water should be calculated based on the given volume of 375 mL. Since we're assuming water to be the solvent, we can consider it to be approximately equal to its density, which is 1 gram per milliliter.

Thus, the mass of water is 375 grams, and dividing this by the molar mass of water (18 g/mol) gives us 20.83 moles of water, not 20.810211 moles. It seems like there was some rounding issue in your calculation.

Now, we can calculate the mole fraction (Xsolvent) by dividing the moles of water by the total moles of both water and NaCl:

Xsolvent = 20.83 moles / (20.83 moles + 0.585216 moles) = 0.9721 (rounded to 4 decimal places)

Next, we can use the formula Psolution = Xsolvent * Psolvent to calculate the vapor pressure of the solution. Given that the vapor pressure of pure water at 55 degrees C is 118.1 torr, we can substitute the values:

Psolution = 0.9721 * 118.1 torr = 114.6 torr (rounded to 1 decimal place)

It seems like you made a rounding error in your calculation, which resulted in a slightly different value for the vapor pressure. The correct answer should be approximately 114.6 torr, not 112 torr.

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