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### Topic: Mass Calculation  (Read 5318 times)

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#### laxplayer

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##### Mass Calculation
« on: November 05, 2007, 05:28:44 PM »
The problem states:
Many gases are shipped in high-pressure containers. Consider a steel tank whose volume is 80.0 L and which contains O2 gas at a pressure of 16300 kPa at 27°C. What mass of O2 does the tank contain in Kg?

I used the formula density=(MM)(P)/(R)(T) I found the molar mass of O2 to be 32, the pressure to be 160 atm, R=.0821, and the temperature 300.15 K.  I found the density to be 207.8. Then I multiplied the density by 80L, the volume, to get 16621.8, which is 1.7 Kg.
It says I got it wrong but I don't know why or what I could have done differently.

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##### Re: Mass Calculation
« Reply #1 on: November 05, 2007, 06:10:16 PM »
Check your conversion to atm - I think it should be 160.87atm.

16621.8, which is 1.7 Kg.
Are you sure?

#### laxplayer

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##### Re: Mass Calculation
« Reply #2 on: November 05, 2007, 06:25:32 PM »
okay, so I plugged 160.87 atm into the equation and it worked! The answer came to be 16.7. I had no idea changing that would make that much of a difference.

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##### Re: Mass Calculation
« Reply #3 on: November 05, 2007, 06:48:02 PM »
16621.8, which is 1.7 Kg.
Doesn't 16621.8 refer to nMr (mass in grams) in the eqn below?
So shouldn't it be 16.6218Kg?

PV=nRT
P/RT=n/V
PMr/RT=nMr/V

Can you explain how you got 1.7Kg?

#### laxplayer

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##### Re: Mass Calculation
« Reply #4 on: November 05, 2007, 08:00:15 PM »
Oh, the first time I just moved the decimal too many places to the left, then I rounded to two sigfigs, so I got 1.7. When I redid the problem I moved the decimal the right amount, haha, stupid mistakes always get me

#### laxplayer

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##### Re: Mass Calculation
« Reply #5 on: November 05, 2007, 08:17:38 PM »
Does anyone know how to figure out this question that goes along with the problem?

At what temperature in Celsius would the pressure in the tank equal 150 atm?

I used the formula T=PV/nR, so I did (150)(80)/(521.875)(.0821) and I got 280.073. Then I subtracted 273.15 to get 6.923 degrees in celsius, but it says I got it wrong