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ideal gas law problems in chemistry help please..?

ideal gas law problems in chemistry help please..? - Chemistry Forum

ideal gas law problems in chemistry help please..? - Chemistry Forum. Discuss chemical reactions, chemistry.


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Old 06-08-2009, 03:17 PM
Pipette Filler
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Default ideal gas law problems in chemistry help please..?



A sample of nitrogen gas was collected over water at 20.C and a total pressure of 1.18 atm. A total volume of 2.60 multiplied by 102 mL was collected. What mass of nitrogen was collected? (At 20.C the vapor pressure of water is 17.5 torr.)

how would we do this. i tried to find the volume and then found the density and then multiplied it together to get grams but then it didnt work....
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Old 06-08-2009, 03:17 PM
Pipette Filler
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Ok
So we have to use the formula PV = nRT
P is in atm and we must subtract the vapor pressure from the total pressure always because the pressure of the nitrogen gas does not include the pressure produced by vapor pressure

And so we convert the 17.5 torr to atm by dividing by 760... and we get .023 atm as water vapor pressure

So 1.18 - .023 is 1.157 atm = P

Now, V is 2.6 times 102 mL as you said so thats 265.2 mL... we have to convert that to liters by dividing by 1000 and we get .2652 L

R is the ideal gas constant 8.3145 J/mol K
T is 20 degrees C + 273.15 K to get 293.15 K

Now lets plug and chug
.023 atm (.2652 L) = n (8.3145 J/mol K)( 293.15 K)
n is in moles
n = 2.5025 * 10^-6

Now just convert that moles to grams of N and you have your answer!
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