Chemistry help?

A 1.00 L flask is filled with Ar by water displacement at 293 K. The atmosperic pressure is 750.6 torr. After correcting (that's the part I really don't understand) for the water vapor in the flask??, determine how many moles of Ar are present. What is the density of Ar at STP.

Answer:
simple use pv-nRT
p=750.6/760 (divide by 760 torr to convert to atomospheres)
v=1
n=?
R=8.314
T=293

(.9876315)(1)=n(8.314)(293)
n(moles)= .00041 moles

Water displacement involves collecting the gas over water. Some water vapor molecules will unavoidably be mixed in with the Ar gas.
All it means by correcting for the water vapor, is that you have to include that in your calculation. Use partial pressures:
Dalton's law of Partial Pressures says:
P(total) = P(Ar) + P (H20)

Then you can use the ideal gas equation:
PV = nRT = m/M (RT)
Remember, m is for mass of Ar and M is for molar mass of Ar.

Then fill in these equations with the information you have:
mols Ar = (Pressure from Argon)(Volume of flask)(Molar mass of Argon)/(R the gas law constant)(Temperature in K)

Then you have mols of Argon, and all you have to do then is calculate the density at STP (which is 0C and 760torr), and for this you use:
density=mass/volume

I don't want to work it out for you, cause that really wouldn't help you much, but I hope this answers your question. It's not pretty written out on here, sorry. Check your textbook if you need to see it neater!

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