What is the molecular weight (g/mol)of an unknown gas that has a density of 4.90 g/L at STP? A)1.10 × 10^-2 B)1.20 × 10² C)1.10 × 10² D)1.20 × 10^-2 E)1.10

Question

Quizplus · Accepted Answer

Using the ideal gas law, PV = nRT, we can rearrange to get n/V = P/RT. At STP, T = 273 K and P = 1 atm, so we have n/V = 1/RT. We can substitute in the density, d = m/V, to get n/(m/d) = 1/RT or n = m/RT * d. We can then solve for the molecular weight using the equation MW = m/n. Plugging in the given density and assuming a volume of 22.4 L/mol at STP, we get:
MW = m/n = d * V / n = 4.90 g/L * 22.4 L/mol / (1 mol/0.08206 L·atm·K·mol·s^-2) = 10.81 g/mol 
which closest to 1.10 x 10^12 (C).

What Is the Molecular Weight (G/mol)of an Unknown Gas That