Question

Calculate the mole fraction of solvent for a sucrose solution contains 20.0 g of sucrose (molar mass 342.3 g/mol) dissolved in 100.0 g of water at 25oc.

Answer 1

Mole fraction = moles of desired compound / total moles

moles = mass (g) / molar mass (g/mol)

Mass of sucrose = 20.0 g
Moles of sucrose = 20.0 g / 342.3 g/mol = 0.058 mol

Mass of water = 100.0 g
Molar mass of water = 18 g/mol
Moles of water = 100.0 g / 18 g/mol = 5.556 mol

Total moles = moles of sucrose + moles of water
                   = 0.058 mol + 5.556 mol
                   = 5.614 mol

Mole fraction of sucrose = moles of sucrose / total number of moles
                                       = 0.058 mol / 5.614 mol
                                       = 0.010