CBSE Class 11-science Answered

Dear Student,

The sum of mole fractions of solute and solvent of a solution is unity or 1.

Explanation:

Mole fraction = Moles of solute or solution / Total moles of solution

If the solution contains n number of moles of solute and N number of moles of solvent, then the total moles of solution = n + N

Therefore,

Mole fraction of solute = n / n + N    -------1

Where, n is the number of moles of solute and N is the moles of solvent.

Mole fraction of solvent = N / n + N  ---------2

Where, n is the number of moles of solute and N is the moles of solvent

The sum of mole fractions of solute and solvent

= Mole fraction of solute +mole fraction of solvent

Substituting values from equations 1 and 2,

Sum of mole fraction of solute and solvent = (n / n + N) + (N / n + N) -------3

On solving 3, 

The sum of mole fraction of solute and solvent = 1 = unity.