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>> Mole Fraction
This method is used when the solution is constituted by mixing two or more components. It is defined as the ratio of number of moles of one component to the tota number of moles of the solution (i.e., all the components). Taking three components A, B and C.
Components A B C
Mass (in grams) W1 w2 w3
Molecular mass m1 m2 m3
No. of g moles w1 w2 w3
m1 m2 m3
Total number of g moles = w1/m1 + w2/m2 + w3/m3
Thus, Mole fraction of A – w1/m1/w1/m1 + w2/m2 + w3/m3 = fA
Mole fraction of B = w2/m2/w1/m1 + w2/m2 + w3/m3 = fB
Mole fraction of C = w3/m3/w1/m1 + w2/m2 + w3/m3 = fC
The sum of mole fractions of a solution is equal to 1,
i.e., fA + fB + fC = 1.
In a binary solution,
Mole fraction of solute + Mole fraction of solvent = 1
Let n moles of solute (A) and N moles of solvent (B) be present in a solution.
Mole fraction of solute = n/N+n = XA
Mole fraction of solvent = N/N+n = XB
Thus, XA + XB = 1
Mole fraction is independent of temperature of the solution.