What is the partial pressure due to the nitrogen gas in the cylinder? for this problem------------->

Question

A gas cylinder contains 5 moles of N2, 8 moles of O2 and 3 moles of He and has a total pressure of 800 mm Hg.

150

250

400

800

Answer 1

PV=nRT, right?   So there is nothing in there about the mass of the gas or its identity, just the number of moles.  And the number of moles are given!!

So there are 5+8+3 moles of gas,  or 16 moles.

You could use that and the pressure (and temperature) to calculate the volume of the container, but then to get partial pressure you'd just have to undo that calculation.   Since T,R, and V are the same for each one, pressure is just proportional to the amount of gas, and it's a simple ratio:

5/16 of the pressure is from N2:  250 mm Hg

8/16 of it is from O2:  400

and 3/16 from He:  150

reality check:  they all add back up to 800.