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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zerofantasym on February 09, 2008, 11:31:51 AM

Title: vapor pressure - answer check
Post by: zerofantasym on February 09, 2008, 11:31:51 AM
What would be the vapor pressure of water at 70 C above a solution made by dissolving 57.980 g of Nickel nitrate Ni(NO3)2 in 288.26 g of water? The vapor pressure of pure water at this temperature is 233.70 mmHg? Assume complete dissociation of solute.

I got 233.68 mmHg. Is this right?
Title: Re: vapor pressure - answer check
Post by: Borek on February 09, 2008, 12:06:01 PM
No, it should be lower.
Title: Re: vapor pressure - answer check
Post by: zerofantasym on February 09, 2008, 01:20:15 PM
hmm ok well this is actually an online homework and I don't know, maybe I'm not entering the answer in correctly.  I tried it twice again  and  got 229.17 mmHg but it's still not correct apparently. What's wrong here?

mol fraction of Ni(NO3)2 = .0194

using Raoult's Law: PA = PA°XA

∆P = 233.70 mmHg x .0194 = 4.534 mmHg
PA = 233.70 - 4.534 = 229.17 mmHg

Title: Re: vapor pressure - answer check
Post by: Borek on February 09, 2008, 01:56:49 PM
Quote from: zerofantasym on February 09, 2008, 01:20:15 PM
mol fraction of Ni(NO3O)2 = .0194

Isn't it dissociated?
Title: Re: vapor pressure - answer check
Post by: zerofantasym on February 09, 2008, 02:08:23 PM
It's what?
Title: Re: vapor pressure - answer check
Post by: zerofantasym on February 09, 2008, 02:37:25 PM
Uh I copied it here wrong. I did it right on the paper though.