[neubecka]

I have measured the total pressure in a small bottle. Thereafter, I have withdrawn 1 mL of the gas. I let the gas expand (to an unknown volume) in the syringe and injected 1 ml into the gas analyzer (H2). How much is the partial pressure of the H2 gas in the bottle?

Volume of bottle headspace is 715 ml.
Total pressure of the entire bottle is 99100 Pa
H2= 54,62 ppm (mole) in 1 ml of the gas expanded to a pressure equal to atmospheric pressure.
Temp=room temp

[Borek]

You have to show your attempts at solving the problem to receive help, this is a forum policy.

[neubecka]

Ah, I see, sorry.

Well, I have tried this:

First calculate the total moles of the bottle, i.e. n=(99100 Pa * 0,000715 m3)/(8,3145m3 Pa K-1 mol-1*298,15 K) = 0,029mol of total gas in bottle

H2 mole = 54,62 ppm/1000000 =5,46^10-5 moles H2 in a syringe of 2ml and an atmospheric pressure

So, if I now want to translate the amount of H2 in the syringe into the bottle, I need to take the pressure and volume of the bottle into account. And I am not sure how I should do this.

Perhaps if I calculate how many ml of H2 in the syringe would contain if the pressure of the syringe was the same as in the bottle:

(5,46^10-5 moles H2*8,3145m3 Pa K-1 mol-1*298,15 K)/99100 Pa = 1,37^10-6 ml

And here I am stuck. I think Im totally wrong.I cannot just compare the volumes with each other? Or?

Thanks.
/A

 

[mjc123]

If you have analysed the extracted sample and found that the mole fraction of H₂ in that sample is 54.62 ppm, then presumably the mole fraction of H₂ in the bottle headspace gas is the same, if your analytical procedure is reliable. This value won't change with changes of pressure or volume.
I wonder if you understand mole fraction, because you say
"H2 mole = 54,62 ppm/1000000 =5,46^10-5 moles H2 in a syringe of 2ml and an atmospheric pressure"
which is nonsense. 54.62 ppm is 5.46 x 10^-5 moles in 1 mole of total gas. Do you think 1 mole of gas occupies 2 mL at atmospheric pressure? Or is your number really a mole fraction?

[neubecka]

Ok, thanks a lot!