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Topic: Physical questions  (Read 4704 times)

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Offline Pirt

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Physical questions
« on: April 07, 2005, 05:10:49 AM »
Hi, hope you can help me with these problems,

1.

I have been given the PV=nRT formula and told to rearrange it to include (d) density, (t) tepm, (M) Mass, and (p) Pressuer which i have done and got to:

PM = dRT.

Now I have been given a table of 'Pressure of CO2 / mm Hg' and
'Weight of CO2 / g'. I have been given varous pressures and weights o CO2 at these presures and told to work out the molecular weight of CO2 using the 'PM=dRT' formula.
 I have been told that for real gases the density must be measured as a function of 'P' to allow M to be determined from the intercept of a plot of d/p vs p.

I was wondering do I first need to work out the individual densities for each weight at a certain pressure, then convert my units of pressure into Pa to make it easier to deal with, then divide my densitiy values by the pressures and plot them values against the pressure. Hopefully the intercept will give me M.

If this makes sense to anyone could youtell me if i have thought about going about it the right way. Thanks

My next question is if somebody could explain what an osmotic cell is please.

Thanks
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Offline Donaldson Tan

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Re:Physical questions
« Reply #1 on: April 07, 2005, 05:56:25 AM »
at low pressure, real gas behaves almost ideally.

PM = dRT where M is the molar mass and d is density

you must ensure the density measurement of the different weight gas are all carried out at the same temperature.

plot a graph of log d (y-axis) against lg P (x-axis)
PM = dRT
d = PM/RT
lg d = lg (PM/RT) = lg P + lg (M/RT)

plot using data with P < 3bar (preferentially)

you should get a graph with gradient 1 and the intercept corresponds to lg (M/RT) where T is temperature
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Offline Pirt

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Re:Physical questions
« Reply #2 on: April 07, 2005, 06:57:00 AM »
Hey,

thanks for the advice, its a lot clearer now!

Thanks

Prit   ;D
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