A quantity of 5.0 g of a mixture of He and another gas occupies a volume of 1.5 l at 300 K and 750 mm Hg. The gas freezes at 270 K. At 15 K, the pressure of the gas mixture is 8 mm Hg (at the same vol

Question

A quantity of 5.0 g of a mixture of He and another gas occupies a volume of 1.5 l at 300 K and 750 mm Hg. The gas freezes at 270 K. At 15 K, the pressure of the gas mixture is 8 mm Hg (at the same volume). What is the molecular mass of the gas?

TestHub · Accepted Answer

At 15 K only He is gaseous: n(He) = PV/RT = (8/760 × 1.5)/(0.0821 × 15) = 0.0128 mol, i.e., 0.051 g He. At 300 K: n(total) = (750/760 × 1.5)/(0.0821 × 300) = 0.0601 mol, so n(gas) = 0.0601 - 0.0128 = 0.0473 mol with mass 5.0 - 0.051 = 4.95 g. M = 4.95/0.0473 ≈ 104 g/mol, closest to 103.8. Confirms Ans: (a) 103.8.

Chemistry - Ideal Gas Question with Solution | TestHub

Options:

Doubts & Discussion