A solution contains 45 grams of nitrogen gas and 40 grams of argon. What is the mole fraction of argon in this solution?
0.45
0.40
0.62
0.38
? How do you find mole fraction in this case?
2 Answers

0.38
You first calculate the total moles by dividing the grams by molecular weight:
45 g N2 / 28.02 g/mol = 1.6 mol N2
40 g Ar / 39.95 g/mol = 1.0 mol
Then you divide the moles of Ar by the total number of moles:
1.0 / (1.6 + 1.0) = 0.38 mol fraction
Source(s): ap chem 
A mole is the quantity such that the mass in grams is comparable to the atomic/molecular weight. Argon has an atomic weight of 40. consequently a million.0 moles of it has a mass of 40 grams.