What is the mole fraction of LiF in an aqueous soltion that contains 39.4% LiF

mole fraction (LiF) =

= (number of mole LiF) / (number of mole LiF + number of mole H2O)

In 100 g solution there are 39.4 g LiF and 100-39.4 = 60.6 g H2O.

1.

M (LiF) = 6.94 + 19.00 = 25.94 g/mol

39.4 g LiF*1mol LiF/25.94 g LiF = 1.519 mol LiF

2.

M (H2O) = 2*1.01 + 16.00 = 18.02 g/mol

60.6 g H2O*1 mol H2O/18.02 g H2O = 3.363 mol H2O

3.

mole fraction (LiF) =

= (1.519 mol LiF) / (1.519 LiF + 3.363 mol H2O) = 0.311

mole fraction (LiF) = 0.311