A balloon with 8.73L contains 0.321 Moles of helium gas.What is the density of the gas?

Question

A balloon with volume of 8.73L contains 0.321 moles of helium gas. What is the density of the gas?

Answer 1

Under these conditions, one mole would occupy 8.73/0.321 = 27.1963 liters.  Since the mass of one mole is four grams, the density is 4/27.1963 = 0.1471 grams per liter.    

Answer 2

density = mass / volume

D = m / V

moles = mass / molar mass

n = m / M or m = n M

D = n M / V = 0.321 mol He x (4.003 grams He / mol He)  / 8.73 L

D = 0.147 g / L

====== Follow up =======

No Tere, the mass is not the molar mass divided by the moles.  That would have units of grams per mole squared.

n = m / M

where n is number of moles, m is the mass and M is the molar mass.

Mass divided by molar mass is g / (g/mol), which is moles

Answer 3

density = mass / volume....since the number of moles of helium gas is given...you can get the mass of helium gas in the ballon using:

mass = molecular wt of He2 / moles of He2

mass = 4.0 g/mole / 0.321 moles

mass = 12.5 g of He2

density =  mass of He2 / volume of He2

density = 12.5 g / 8.73 L

density = 1.43 g/L