Mole fraction is defined as the number of moles of a component of a solution divided by the total number of moles of all components.

The Mole fraction is expressed as :
$\mathrm{mole\; fraction\; of\; solute}=\frac{\mathrm{moles\; of\; solute}}{\mathrm{moles\; of\; solute}+\mathrm{moles\; of\; solvent}}$

$\mathrm{mole\; fraction\; of\; solvent}=\frac{\mathrm{moles\; of\; solvent}}{\mathrm{moles\; of\; solute}+\mathrm{moles\; of\; solvent}}$

Example 1:
Calculate the mole fractions of sugar and water in a solution made by dissolving 200g of sugar in 1 liter of water? Molecular weight of water(H₂O) = 18, Molecular weight of sugar(sucrose) = 342 and 1 liter of water is approximately 1000g.

$\mathrm{moles\; of\; water}=\frac{\mathrm{grams}}{\mathrm{molecular\; weight}}=\frac{\mathrm{1000}}{\mathrm{18}}=\mathrm{55.56}$

$\mathrm{moles\; of\; sugar}=\frac{\mathrm{grams}}{\mathrm{molecular\; weight}}=\frac{200}{342}=0.58$

$\mathrm{mole\; fraction\; water}=\frac{55.56}{0.58+55.56}=0.989\mathrm{mole}$

$\mathrm{mole\; fraction\; sugar}=\frac{0.58}{0.58+55.56}=0.01\mathrm{mole}$