[streetlegal08]

Hey, people could you help me with this? It is a gas pressure problem that involves the use of several laws. It goes like this:
"What would be the partial pressure of oxygen in the following experiment? A collapsed polyethylene bag of 30L capacity is partially blown up by the addition of 10L of nitrogen. Measure at 0.965atm and 298K. Subsequently, enough oxygen is pumped into the bag, so that at 298K and 0.990atm external pressure the bag contains a full 30L. Assume ideal behavior" Please help me 

[Borek]

What do you know about the problem? What do you need to calculate the final answer?

[streetlegal08]

What do you know about the problem? What do you need to calculate the final answer?

I know the volume, temperature, and pressures? I suppose that what it means by saying "Assume ideal behavior" is that I need to use the Ideal Gas Law to find the partial pressure of oxygen, but to do that I'd have to use Dalton's... ok im confused :S

[Borek]

You are on the right track.

Can you calculate how many moles of nitrogen was initially present?

Can you calculate how many moles of the gas was finally present in the inflated bag?

[streetlegal08]

You are on the right track.

Can you calculate how many moles of nitrogen was initially present?

Can you calculate how many moles of the gas was finally present in the inflated bag?

I don't know how to calculate the moles of nitrogen when I get 2 volumes 2 pressures 2 temperatures... how can I calculate it?

[Borek]

What are volume, temp and pressure of just nitrogen, before oxygen was added?

[streetlegal08]

What are volume, temp and pressure of just nitrogen, before oxygen was added?

lol thank you for helping me realize that! 0.965atm pressure and 298K in 10L of nitrogen.
n=PV/RT so that'd b  N=(0.965atm)(10L)/(0.0821 atmL/ molK)(298K) = 3.94*10^-1 mol?

[Borek]

Wasn't that hard

[streetlegal08]

Wasn't that hard

haha your right ... but what comes next, I'm supposed to find the partial pressure of oxygen... how can I relate this to Dalton's Law?

[Borek]

Can you calculate how many moles of the gas was finally present in the inflated bag?

[streetlegal08]

Can you calculate how many moles of the gas was finally present in the inflated bag?

ok there were 1.21moles of gas in the fully inflated bag, and 3.94x10^-1moles of nitrogen initially, so would that mean that if I substract the 1.21moles of gas minus the 3.94x10^-1 moles of nitrogen then I get the moles of oxygen... I hope I'm right, therefore, there were 0.816 moles of oxygen in the fully inflated bag. Please tell me if I'm doing the correct thing here... if I use the moles of oxygen to find P, will it be the oxygen partial pressure? like this:
P=nrt/v   which'd be   P=(0.816mol O)(0.0821 atm L/ mol K) (298K)/ 30L

P=0.665 atm final partial pressure of O??? makes sense since there is 1/3 of nitrogen in the bag, 1/3 of .990atm, and there are 2/3 of oxygen in the bag, 2/3 of .990 which makes sense for the number to be 0.665...
am I right?

[Borek]

Looks OK to me.

[streetlegal08]

Looks OK to me.

well, ditto... and that is actually pretty reassuring... thank you man I owe you one.