A 41.1-g sample of Ne gas exerts a certain pressure in a container of fixed volume.What mass of Ar is required to exert half the pressure at the same conditions of volume and temperature?
A)81.4 g Ar
B)1.02 g Ar
C)163 g Ar
D)821 g Ar
E)40.7 g Ar

Question

Quizplus · Accepted Answer

The pressure a gas exerts in a container at a fixed volume and temperature is directly proportional to the number of moles of the gas (according to the ideal gas law, PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature). Since Ne and Ar are both noble gases, they behave similarly under the same conditions. To exert half the pressure, you need half the number of moles of Ar as there are of Ne in the original sample. The molar mass of Ne is approximately 20.18 g/mol, and the molar mass of Ar is approximately 39.95 g/mol. The number of moles of Ne in the 41.1 g sample is 41.1 g / 20.18 g/mol ≈ 2.04 moles. Half of this amount is 1.02 moles. The mass of Ar required to have 1.02 moles is 1.02 moles * 39.95 g/mol ≈ 40.7 g. Therefore, the correct answer is 40.7 g of Ar, which is choice E.

A 411-G Sample of Ne Gas Exerts a Certain Pressure in in a Container