Ideal Gas Laws: Molar Mass And Density

Question

Uranium hexafluoride is a solid at room temperature, but it boils at 56°C. Determine the density of uranium hexafluoride at 70.°C and 747 torr.

Density= g/L

Answer 1

When given a problem like this and working with gases, it's usually a good idea to assume you have a volume of 1 liter, and then proceed from there. In this problem, the pressure is 747 torr, which we will convert to atm, and we'll convert 70ºC to Kelvin.

747 torr x 1 atm/760 torr = 0.983 atm

70ºC + 273 = 343K

Now, we can use the ideal gas law PV = nRT and solve for moles. Once we get out moles, we can calculate molar mass of UF6 and then density is simply mass/volume.

n = PV/RT = (0.983 atm)(1 L) / (0.0821 Latm/Kmol)(343K

n = 0.0349 moles UF6

molar mass UF6 = 352 g/mol

Since we have 0.0349 moles/L we convert that to gram / liter to get density:

0.0349 moles/L x 352 g/mol = 12.3 g/L = 0.0123 g/ml

Answer 2

density = MP/RT If you use M, molar mass in g/mole, P in atm, R = .0821 liter atm/mole K, and T in Kelvin, you will get density in grams/liter.