Physics question! help please!

Party stores sell small tanks containing 44g of helium gas.
If you use such a tank to fill 0.020 m^3 foil balloons (which don't stretch, and so have an internal pressure that is very close to atmospheric pressure), how many balloons can you expect to fill? Assume the temperature is 20 degrees celcius.
Thanks

Use the Ideal Gas Law to find the mass of helium in each balloon:



P = pressure
V = volume
n = number of moles of gas
R = universal gas constant
T = absolute temperature

PV = nRT

(101300 N/m^2)(0.020 m^3) = n(8.314 J / mole-Kelvin)(273.15K + 20K)
2026 J = n2437J
n = 2026 / 2437
n = 0.831 moles per balloon

The atomic weight of helium is 4.00, so there are 4.00 grams per mole so the mass of helium in each balloon is:

( 0.831 moles per balloon )( 4.00 grams/mole)
= 3.33 grams per balloon

So the number of balloons is

( 44 g ) / ( 3.33 grams per balloon )

13.2 balloons.

Round down to

13 balloons.

This looks like an ideal gas law problem -> PV = nRT

You can find the number of moles of gas you have using the mass of your helium (44g).

n = 44g / (4g / mol) = 11 mol.

You can then find the total volume that this helium will fill at P = 1atm, T = 20 C using:
V = nRT / P

Take this volume and divide by the volume of your balloon to determine how many balloons you can fill:

number_balloons = V / (volume balloon)

Make sure to mind your units!