what is the density in G/L, what is the molecular weight?

Question

A 4.64×10^-2 mol sample of Ar gas is contained in a 2.00 L flask at room temperature and pressure. What is the density of the gas, in grams/liter, under these conditions?

A 0.255 mol sample of an unknown gas contained in a 8.00 L flask is found to have a density of 2.27 g/L. The molecular weight of the unknown gas is  g/mol.

Answer 1

4.64x10-2 mol Ar x 1 mol Ar/39.95 g = 1.16x10^-3 g

1.16x10^-3 g/2 L = 5.81x10^-4 g/L

5.81x10^-4 g/L x 1L/1000 ml = 5.81x10^-7 g/ml

8.00 L x 2.27 g/L = 18.16 g of unknown gas

Molecular weight = grams/mole = 18.16 g/0.255 moles = 71.2 g/mole