Vapour Pressure Depression Chad's Quiz

[Toadesque]

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This question bugs me every time I do it because I don't quite get it

How do you know there will be 1000g of water for every 5.5 moles of CH3OH? What concept is being applied there?

 

[supergenius310]

This is a molality problem....5.5 moles per 1kg solvent (H20). It is asking for vapor pressure of H20...so you find the total moles of H20 in the entire solution, which included 1k H20 and 5.5 moles of the other thing. Find moles of H20 and add to the other thing. Find mole fraction of moles of H20 over the moles of solution. Multiply the mole fraction by the pure vapor pressure of 18 and you get your answer 🙂

 

[Toadesque]

Molality...of course, god I'm so dumb. Thanks! 😀