Question

calculate the mole fraction of each component when a solution is prepared by dissolving 31 g of ethylene glycol in 18 g of H2O​

Answer 1

Step I : Moles of ethylene glycol ( n")

• Mass of ethylene glycol ( W ) = 31 g

• Molar mass (M ) = 67 g

we know that ,

⟹ n" = W / M

⟹ n" = 31 / 67

⟹n "= 0.46

Step II : Moles of water  ( n ')

• Mass of water ( W' ) = 18 g

• Molar mass of water (M' ) = 18 g

we know that ,

⟹ n' = W' / M '

⟹ n '= 18 / 18

⟹n' = 1

Step III : Total moles

⟹ n = n" + n'

⟹ n = 0.46 + 1

⟹ n = 1.46

Step IV : Mole fraction of ethylene glycol ( solute)

As per the formula ,

⟹ X = n " / n " + n '

⟹ X = n " / n

⟹ X = 0.46 / 1.46

⟹ X = 0.7

Step V : Mole fraction of water ( solvent )

Remember ,

⟹ X = X " + X ' = 1

here ,

• X = Mole fraction of the solution

• X " = Mole fraction of the solute

• X ' = Mole fraction of the solvent

hence ,

⟹ X " + X ' = 1

⟹ X ' = 1 - 0.3

⟹ X ' = 0.7

∴ Mole fraction of ethylene glycol is 0.3

∴ Mole fraction of water = 0.7