Equal masses of helium and oxygen are mixed in an empty container at 25^ C . What is the fraction of the total pressure exerted by helium?

Step-by-step solution

Dalton's Law of Partial Pressures states that the partial pressure of each gas in a mixture equals its mole fraction times the total pressure. Let m be the equal mass of helium and oxygen, measured in grams. The molar mass of helium is M_ He = 4 g/mol , and that of oxygen is M_ O ₂ = 32 g/mol . The mole of helium is n_ He = m 4 , while the mole of oxygen is n_ O ₂ = m 32 . The total number of moles becomes: n_ total = m 4 + m 32 = 8m 32 + m 32 = 9m 32 The mole fraction of helium is thus: X_ He = n_ He n_ total = m