## Formula :

$$\text{Mole Fraction}\;=\;\frac{\text{Moles of Solute}}{\text{Moles of Solute}\;+\;\text{Moles of Solvent}}$$

Example-1: 0.100 mole of NaCl is dissolved into 100.0 grams of pure H2O. What is the mole fraction of NaCl?

Solution:

$$\frac{100.0\text{g}}{18.0\text{g}\;\text{mol}^{-1}}\;=\;5.56\text{mol of}\;H_2O$$

Add that to the 0.100 mol of NaCl = 5.56 + 0.100 = 5.66 mol total

$$\text{Mole fraction of NaCl}\;=\;\frac{0.100\text{mol}}{5.66\text{mol}}\;=\;0.018$$

What is the mole fraction of the H2O?

$$\frac{5.56\text{mol}}{5.66\text{mol}}\;=\;0.982$$