Mole Fraction describes the number of molecules contained within one component divided by the total number of molecules in a given mixture. It is quite useful when two reactive-natured components are mixed together. The ratio of both the components is known as the mole fraction. It is a vital chapter of Class 11 that will also come for all the competitive exams that are held such as IIT ones, JEE Mains and NEET.
Understand the concept of mole fraction as it will help you get through the advanced concepts and principles of chemistry later. Use solved examples to find out how this concept has been used and learn to approach problems in the exercise judiciously.
It is advised that the students learn the concept of Mole Fraction primarily by practising problems and getting them verified against the answers on the articles provided on our website. This chapter is not to be left aside for last moment studying as this is an easy concept and can help in fetching good marks with little effort.
Formula Related to the Mole Fraction
Consider a solution that consists of two substances A and B, then the mole fraction of each substance is:
Mole fraction of solute = (Moles of Solute) / (Total number of moles of the solutes and the solvent).
= XA = (mol A) / ( mol A + mol B)
= XB = (mol B) / ( mol A + mol B)
In the given mixture, the sum of all the mole fractions present is equal to one
XA + XB = 1.
When the mole fractions are multiplied by 100, they give the mole percentage.
Mole fraction is a unitless and dimensionless expression.
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The image shows some chemical solutions of which we can find the mole fraction of its components.
Advantages of Mole Fraction
The advantages of mole fraction are:
Mole fraction has never been dependent on the temperature.
To calculate the mole fraction, it is not necessary to find out the information about the density of the phase.
The mole fraction is represented by the ratio of partial pressure to the total pressure of the mixture, in the case of an ideal gas mixture.
Disadvantages of Mole Fraction
There is only one disadvantage of mole fraction, that is, mole fraction is not convenient for liquid solutions.
Properties of Mole Fraction
The properties of mole fraction are:
It is temperature independent which prevents it from variations when the temperature fluctuates. The knowledge of the densities of the phase involved is not necessary in the case of the mole fraction.
By weighing off the actual masses of the constituents, a mixture of a known mole fraction can be prepared.
The measure is symmetric, i.e., in the mole fraction x = 0.1 and x = 0.9, the roles of ‘solvent’ and ‘solute’ are reversed.
In a ternary mixture, a mole fraction of a component can be expressed as functions of other components’ mole fraction and binary mole ratios.
Calculate the mole fraction of NaCl and H₂O, if 0.010 moles of NaCl is dissolved in 100 grams of pure water.
The molecular weight of water is considered to be 18.0153 grams per mole.
Number of moles of water = 100 grams / 18.0153 grams = 5.56 moles
Mole fraction of NaCl = 0.100 moles / ( 5.56 moles + 0.10 moles)
= 0.100 moles / 5.66 moles
Mole fraction of NaCl = 0.018
Mole fraction of H₂O = 5.56 moles / 5.66 moles
Mole fraction of H₂O = 0.982
Calculate the mole fraction of acetone that is present in a solution which consists of 2 moles of benzene, 3 moles of carbon tetrachloride, and 5 moles acetone.
Number of moles of acetone = 5 moles
Number of moles of carbon tetrachloride = 3 moles
Number of moles of benzene = 2 moles
Total number of moles in the solution = number of moles present in acetone + number of moles present in carbon tetrachloride + number of moles present in benzene
= 5 moles + 3 moles + 2 moles
= 10 moles
Mole fraction of acetone = (Number of moles in acetone) / (Total number of moles in the solution)
= 5 moles / 10 moles
Mole fraction of cabon tetrachloride = (Number of moles in carbon tetrachloride) / (Total number of moles in the solution)
= 3 moles / 10 moles
Mole fraction of benzene = (Number of moles in benzene) / (Total number of moles in the solution)
= 2 moles / 10 moles
A solution is prepared by mixing 30 grams of ethanol and 30 grams of water. Determine the mole fraction of each component.
The molecular weight of ethanol is fixed at 46.07 g/mol.
The number of moles of ethanol present in the solution = 30 grams / 46.07 g/mol = 0.651 moles.
The molecular weight of water is fixed at 18g/mol.
The number of moles of water present in the solution = 30 grams / 18 g/mol = 1.67 moles
Total number moles = 0.651 + 1.67 = 2.321 moles
Mole fraction of ethanol = 0.651 moles / 2.321 moles = 0.28
Mole fraction of water = 1.67 moles / 2.321 moles = 0.72