Question

Define Mole fraction.

Answer 1

Mole fraction is a unit of concentration. It depicts the fraction of moles of a particular component in a solution. It is a unitless fraction.

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Complete step by step answer:

Mole fraction of a particular component is defined as the number of moles of the same component of a solution to the total number of moles of all the constituents of the solution. Mole fraction is also known as the amount fraction. The expression of mole fraction of ith component in a solution is:

${x_i} = \dfrac{{{n_i}}}{{{n_{total}}}}$

The sum of all the mole fractions of all constituents in a solution is equal to 1.

$\sum\limits_{i = 1}^N {{x_i}} = \sum\limits_{i = 1}^N {\dfrac{{{n_i}}}{{{n_{total}}}}}$

$\sum\limits_{i = 1}^N {{x_i}} = \dfrac{{{n_1} + {n_2} + ... + {n_N}}}{{{n_{total}}}}$

$\sum\limits_{i = 1}^N {{x_i}} = \dfrac{{{n_{total}}}}{{{n_{total}}}} = 1$

The mole fraction is sometimes donated by the Greek letter χ (chi) instead of Roman x.

Some properties of mole fraction are:

It is temperature independent.

Mole fraction can be expressed as the ratio of partial pressure to the total pressure in a mixture of ideal gases.

It is very frequently used in the construction of phase diagrams.

It is always less than 1 as the number of moles of a constituent cannot exceed the total moles of all the constituents in that solution.

If mole fraction is known, the mixture can be prepared by weighing off appropriate masses of the components.

Note: One can confuse mole fraction with molar concentration or mass fraction. While mole fraction is a unitless fraction, molar concentration is a quotient of moles to volume and mass fraction is a ratio of mass and moles.