Mole Fraction – Definition and How to Calculate Mole Fraction?

Introduction to Mole Fraction

Mole fraction refers to a unit of concentration. It is a formula in the field of physics that is unitless expression. Mole fraction is equal to the number of a component’s moles divided by the total number of a solution’s moles.

Also, when analyzing the solutions chemist use mole formula to measure the concentration of components. Besides, in this topic, we will discuss the definition of this unit and how to calculate it.

What is Mole Fraction

Simply we can say that this formula refers to the ratio of the number of moles solute to the total number of moles of solute and solvent in a solution. Furthermore, it is the ratio of moles to moles also it is always less than one.

Moreover, in any solution, the mole fraction of solute A is = moles of A / total moles.  In addition, the mole fraction of the solvent = moles of solvent / total moles. Besides, in some cases, the mole number is not given directly. So, you have to find it using the chemical formula of the compounds their weight or their volumes.

Definition of Mole Fraction

In the periodic table, every element has a characteristic mass, and by its virtue of this, every compound also has a characteristic mass. Also, at the atomic level, scientist measure atomic mass in atomic mass units. But, chemists need to convey mass in macroscopic terms.

So, to end this issue they defined mole of nay compound and elements as Avogadro’s number (6.022 × 10²³) of molecules or atoms. Furthermore, the scientists measure the mass of these many particles in grams and are the same number as the scientist measures the atomic mass units of the molecular mass.

In simple words, we can say that the mole fraction is the ratio of the mole of a solvent to the total number of moles.

Use of Mole Fraction Equation

This formula is easy to use if you know the number of moles of all the solutes and solvents. For illustration, suppose you have 2 two moles of CCl₄ (Carbon tetrachloride), 4 moles of C₃H₆O (acetone), and 3 moles of C₆H₆ (Benzene).

In this solution, the total number of moles is 9. Also, the equation informs us that that the mole fraction of carbon tetrachloride is 2 / 9 = 0.22, the mole fraction of acetone is 4 / 9 = 0.44, and the mole fraction of benzene is 3 / 9 = 0.33.

Besides, things get complicated if you only know the mass one or more components of the solution. In addition, you just have to convert the mass of components to the number of moles, as long as you know the chemical formula.

Example problem

Now this example will help you understand the mole fraction more clearly. Suppose you dissolve 77 gram of carbon tetrachloride in 78 gram of acetone. So, now what will be the mole fraction of this compound?

First of all, convert the masses to the number of moles of each compound, and use the periodic table for the atomic masses of the elements. Besides, the atomic mass unit of carbon is 12.0 amu (rounding to one decimal place) and of chlorine, the amu is 35.5. So, one mole of carbon tetrachloride weighs 154 grams. And you have 77 grams which mean 77 / 154 = 0.5 moles.

The amu of hydrogen is 1 and oxygen is 16 amu. So, the molar mass of acetone is 58 grams. You have 78 grams which come to 58 / 78 = 1.34 moles. This means the total number of moles in the solution is 0.5 + 1.34 = 1.84

Now using the mole fraction equation

Mole fraction of carbon tetrachloride = 0.5 / 1.84 = 0.27

Mole fraction of acetone = 1.34 / 1.84 = 0.73

Solved question for you

Question. What is the atomic mass of the helium?

A. 5.002602

B. 4.002602

C. 2.002602

D. 6.002602

Answer. The correct answer is option B.