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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.

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