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### Topic: ppmv and the ideal gas law  (Read 865 times)

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#### spacebee

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##### ppmv and the ideal gas law
« on: March 10, 2022, 08:15:49 PM »
Hi,

I am studying for my PE exam and there is an equation in my notes that relates concentration ppmv (Cppmv) to the ideal gas law:

Cppmv/10^6 = (mass*Runiversal)/(Pressure*Volume*MW)

I understand PV=nRT and that n=mass/molecular weight, what I cannot figure out is how Cppmv and 10^6 found their way into the equation. The right side of the above equation is the gas law with all of the variables on one side, but the left side?? Please *delete me*

Nastassja

#### Hunter2

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##### Re: ppmv and the ideal gas law
« Reply #1 on: March 11, 2022, 01:04:49 AM »
1. Temperature  is missing.
2. For what stands cppmv

#### Borek

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##### Re: ppmv and the ideal gas law
« Reply #2 on: March 11, 2022, 03:07:05 AM »
This is just a definition - Cppmv and 106 are there to define the Cppmv, it is not like it is some solution to some problem, one that can be derived from other equations.
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#### mjc123

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##### Re: ppmv and the ideal gas law
« Reply #3 on: March 11, 2022, 08:33:52 AM »
The RHS equals nR/PV = 1/T. This is not equal to any kind of concentration.

#### Aldebaran

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##### Re: ppmv and the ideal gas law
« Reply #4 on: March 11, 2022, 09:48:52 AM »
You can in fact rearrange the gas equation to give concentration: n/v =P/RT. This will give mol/litre or cubic metre or whatever depending what units you are looking for. You could then further change the units to ppm if you want to I suppose  However I’m not entirely clear what the OP is trying to achieve.

#### Borek

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##### Re: ppmv and the ideal gas law
« Reply #5 on: March 11, 2022, 10:30:10 AM »
I assumed missing T was just a typo.

You can in fact rearrange the gas equation to give concentration: n/v =P/RT.

Good point. Still, n/V is just a definition, it doesn't have to be a "solution" of something.
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#### billnotgatez

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##### Re: ppmv and the ideal gas law
« Reply #6 on: March 11, 2022, 10:43:10 AM »
or poor note taking

I assumed missing T was just a typo.
...
... there is an equation in my notes that relates concentration ppmv (Cppmv) to the ideal gas law:
Cppmv/10^6 = (mass*Runiversal)/(Pressure*Volume*MW)
...

#### spacebee

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##### Re: ppmv and the ideal gas law
« Reply #7 on: March 11, 2022, 11:19:27 AM »
T was a typo and my notes are a printout. I tried to edit my post, but it didn't look like I could.

My online PE instructor was asking this question: What volume of toluene in ml (density = 0.866 g/cm^3, MW = 92 g/mol) is needed to make a concentration of 200 ppmv in a 10ft by 12 ft by 22 ft chamber when atmospheric pressure is 600 mmHG and temp is 23 Celsius.

He proceeded to find the mass in grams of toluene like this:

Cppmv = (m*Ru*T*10^6)/(P*V*MW)

$$C_{ppmv}=\frac{m\times R\times T\times 10^6}{P\times V\times M_W}$$

200ppmv = [m*(2.2 mmHG ft^3/Kmol)*296 K*10^6]/(600mmHG*10ft*12ft*22ft*98g/mol) where m = 48g

I do not understand the above equation or his usage of it or however you want to say it.

Then he used density to get the ml.
« Last Edit: March 11, 2022, 04:00:58 PM by Borek »

#### spacebee

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##### Re: ppmv and the ideal gas law
« Reply #8 on: March 11, 2022, 11:31:49 AM »
1. Temperature  is missing.
2. For what stands cppmv

T being missing was a typo.

Cppmv stands for concentration in parts per million by volume.

#### spacebee

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##### Re: ppmv and the ideal gas law
« Reply #9 on: March 11, 2022, 11:33:17 AM »
or poor note taking

I assumed missing T was just a typo.
...
... there is an equation in my notes that relates concentration ppmv (Cppmv) to the ideal gas law:
Cppmv/10^6 = (mass*Runiversal)/(Pressure*Volume*MW)
...

Poor note transcribing to this forum. Notes are a handout.

#### mjc123

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##### Re: ppmv and the ideal gas law
« Reply #10 on: March 11, 2022, 04:01:51 PM »
OK, let's do it a bit at a time.
What is m/MW?

#### spacebee

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##### Re: ppmv and the ideal gas law
« Reply #11 on: March 11, 2022, 07:17:42 PM »
OK, let's do it a bit at a time.
What is m/MW?

mass/molecular weight = mol or n from PV=nRuT

#### Borek

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##### Re: ppmv and the ideal gas law
« Reply #12 on: March 12, 2022, 03:30:06 AM »
Can you use this n to calculate volume the gaseous toluene would have under the pressure of 600 mmHg?
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#### romitesur

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##### Re: ppmv and the ideal gas law
« Reply #13 on: May 07, 2022, 04:56:43 AM »
You can in fact rearrange the gas equation to give concentration: n/v =P/RT. This will give mol/litre or cubic metre or whatever depending what units you are looking for.