[Immortal]

Consider a solvent whose molecular weight is 200.0 amu and whose vapor pressure at 25 ºC is 35.00 mm Hg. A sample of 100.0 g of a solute whose molecular weight is 100.00 amu is dissolved in 1.000 kg of that solvent. The solute is not an electrolyte. The vapor pressure of the pure solute is 0.01 mm Hg at 25 ºC. What is the vapor pressure of the solution at 25 ºC?

Hi i was wondering if anyone knows where i can start. Someone told me to use Molar Fractions but this problem is confusing. i dont really understand whats goin on. might also be related to Raoult's law: Pa=XaP'a, Pa=Vapor Pressure of the solution Xa=Mole Fraction of solvent P'a=Vapor Presure of pure solvent. but how would i use it?.. they give Vapor pressure of the pure solvent. but i dunno how to compile the other information nor do i know what they mean...any help is appreciated

[Borek]

Start calculating molar fractions, this was a good advice. Start converting everything to moles.

http://www.chembuddy.com/?left=concentration&right=molar-fraction

Note that vapor peesure of the solute is so low (compared with solved) that it can be neglected.

[Immortal]

How do u calculate the moles of an unknown substance, with grams. and am i suppose to 1amu=1.66054E-24g?

[Immortal]

So we have a 100 g, 100amu solute and a 200g 200 amu solvent and another 1000g solvent?.. confusing question...

[Immortal]

ok nvm someone helped me get the solution. if anyone wanted to know its.. Psol'n = 35 mm Hg x (1000g/200) / ( 1000/200 + 100/100)

[Borek]

ok nvm someone helped me get the solution. if anyone wanted to know its.. Psol'n = 35 mm Hg x (1000g/200) / ( 1000/200 + 100/100)

This is only partially correct - molar fraction of the solvent is calculated OK (using dependence between amu and molar mass that you were not aware off). However, you are asked about total pressure, not partial pressure of the solvent - thus you should add analogical expression describing partial pressure of the solute. Or - as it will be neglectably small - you may comment above result writing 'pressure of solute neglected'. As it is now it is just incomplete.