P-Chem question, activity and vapor pressure

[brzozowskir2]

Hey this question has me stumped and I could really use some help:

 

What is the activity of liquid water in a multicomponent system in which the vapor pressure of water is 748.2 mmHg at 100.0 degrees Celsius?

 

That is all the information given. I think I am probably missing something obvious here, but every equation I have to find activity requires some other info, ie mole fraction or partial pressure.

 

Any help will be greatly appreciated.

Thanks, RB

[insane_alien]

you have the partial pressure of water.

[brzozowskir2]

i have the vapor pressure of the pure liquid, not the partial pressure in the system...i think

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i would need the mole fraction to find the partial pressure using Raoult's law

[insane_alien]

it says the vapour pressure of water in the system is 748.2 mmHg this is it partial pressure.

 

if it was pure water at 100*C then it would be 760mmHg

[brzozowskir2]

lol like i said i was missing something obvious. im an idiot, been studying since 10am.

thanks a lot, sir