[orgo814]

"In an attempt to determine an accurate value of the gas constant, R, a student heated a container of volume 20.000 dm^3 filled with 0.25132 g of helium gas at 500 Celsius and measured the pressure as 206.402 cm of water in a manometer at 25 Celsius. Calculate R (in J) from this data (density of water is 0.99707 g/cm^3)

Okay so R = PV/NT. To calculate P Im multiplying the density by gravity acceleration (9.8 m/s^2) x height. I'm having issue with this step. Im multiplying (9.8 m/s2)(2.0642 m)(997.07 kg/m3) I get an insanely high number for my pressure which throws my R value off. Can someone explain what I may be doing wrong?

[sjb]

"In an attempt to determine an accurate value of the gas constant, R, a student heated a container of volume 20.000 dm^3 filled with 0.25132 g of helium gas at 500 Celsius and measured the pressure as 206.402 cm of water in a manometer at 25 Celsius. Calculate R (in J) from this data (density of water is 0.99707 g/cm^3)

Okay so R = PV/NT. To calculate P Im multiplying the density by gravity acceleration (9.8 m/s^2) x height. I'm having issue with this step. Im multiplying (9.8 m/s2)(2.0642 m)(997.07 kg/m3) I get an insanely high number for my pressure which throws my R value off. Can someone explain what I may be doing wrong?

Do thr units work out for this?

[orgo814]

When I did it, yes. Can you pinpoint where I am missing it?

[mjc123]

Taking your numbers, multiplying (approximately) 10 x 2 x 1000 = 20 000 Pa, which sounds right, given that 1 atm (101 325 Pa) corresponds to about 10 m of water. What makes you think it is "insanely high", and what value of R do you get that you think is off?
You weren't thinking of it as 20 000 atm were you? Or using a value of 20 for V as if it was 20 m³?

[orgo814]

When solving for R with that pressure, I use m3. I'm getting a high value for R (by placement of decimal point)

[mjc123]

I get 8.30 J/mol/K, which is pretty close. Please show your working, so we can "pinpoint where you're missing it".

[Enthalpy]

I too get 8.3 so it's probably the unit mess that achieved to mislead you.
Which is realistic: real life is worse than that, with imperial units, optical units, and so on.

For my personal information: this manometer gives the absolute pressure, how can it use water? Vapour pressure must make it wrong.

[mjc123]

And how would it measure 206.402 cm water to 6 sig figs?