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Topic: What is the molar mass?  (Read 2266 times)

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Offline ch3mgirl

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What is the molar mass?
« on: April 21, 2011, 01:09:22 PM »
I just need to make sure I did this correctly...

If we dissolve 84.9mg of an unknown molecular material in 100.0mL of water, the resulting solution has an osmotic pressure of 188 torr at 27.0 degrees Celsius. What is the molar mass of the unknown material?

84.9mg/100mL = 0.849g/L
188 torr * (1 atm/760 torr) = 0.247 atm
27 + 273 = 300K

Then, I just plugged everything in.

0.247atm = (0.849g/molar mass)(0.0821)(300K)
And rearranged to solve for molar mass and ended up with 84.66g/mol.
Is this correct?  ???
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Offline rabolisk

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Re: What is the molar mass?
« Reply #1 on: April 21, 2011, 01:23:29 PM »
Correct, assuming this compound doesn't dissociate.
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Offline ch3mgirl

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Re: What is the molar mass?
« Reply #2 on: April 21, 2011, 01:28:06 PM »
Quote from: rabolisk on April 21, 2011, 01:23:29 PM
Correct, assuming this compound doesn't dissociate.

Thanks so much! If my compound was ionic then I would need to factor that in, right?
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Offline rabolisk

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Re: What is the molar mass?
« Reply #3 on: April 21, 2011, 01:35:23 PM »
Right. Of course, the question did say unknown molecular material, so my point is moot.
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