Need help on a Gas Law question please?

Question

A 12.0 gram sample of He(g) occupies a volume of 25.0L at certain temperature and pressure. What volume does a24.0 gram sample of Ne (g) occupy at these conditions of temperature and pressure?

Choices

A. 9.92 L

B. 14.8 L

C. 22.4 L

D. 25.0 L

E. 50.0 L

The correct answer is A. 9.92 L, but I do not now the calculations to get to 9.92. Any help is much appreciated

Answer 1

You need to determine how many moles you have of each.  The difference in the volume will then be a ratio...

Ideal gas law is PV = nRT.  Rearrange to V/n = RT/P.

So...V/n of He needs to equal V/n of Ne!

Answer 2

12.0 g He x 1 mol He/4.00 g He=3.00 mol He

24.0 g Ne x 1 mol Ne/20.18 g Ne=1.19 mol Ne

PV=nRT

P x 25.0 L=3.00 mol x R x T  <===equation 1

P x V=1.19 mol  x R x T <===equation 2

rearrange second equation

V=(1.19 mol  x R x T)/P

divide second equation by first equation

V/(P x 25.0 L)=((1.19 mol  x R x T)/P)/(3.00 mol x R x T)

isolate V and simplify

V=(P x 25.0 L x 1.19 mol x R x T)/(P x 3.00 mol x R x T)

cancel all like terms and we're done!

V=9.92 L

So answer A. 9.92 L is correct.