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Mole fraction (x)

subtopicmedium~25 min study8 MCQ

Ratio of moles of one component to the total moles of all components in a solution.

Practice 8 questionsBack to syllabus~12 min

What is Mole fraction (x)?

A measure of concentration defined as the ratio of the number of moles of a particular component to the total number of moles of all components in a mixture or solution.

Key formula / rule: Mole Fraction of component i

Key points

  • Define mole fraction.
  • Calculate the mole fraction of a component in a binary and multi-component solution.
  • Understand the relationship between mole fractions of different components.
  • Recognize the advantages of using mole fraction as a concentration unit.

Common exam trap

Confusing mole fraction with mole percentage (multiplying by 100).

Definitions

Term

Mole Fraction

Meaning

A measure of concentration defined as the ratio of the number of moles of a particular component to the total number of moles of all components in a mixture or solution.

Learning objectives

  • Define mole fraction.

  • Calculate the mole fraction of a component in a binary and multi-component solution.

  • Understand the relationship between mole fractions of different components.

  • Recognize the advantages of using mole fraction as a concentration unit.

Formulae

Name

Mole Fraction of component i

Note

where ni is the number of moles of component i, and Σnj is the total number of moles of all components in the solution.

Expression

xi = ni / Σnj

Name

Sum of Mole Fractions

Note

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

Expression

Σxi = 1

Prerequisites

  • Concept of moles.

  • Calculation of molar mass.

  • Understanding of solutions and components.

Common mistakes

  • Confusing mole fraction with mole percentage (multiplying by 100).

  • Incorrectly calculating the total number of moles.

  • Using mass instead of moles in the calculation.

Keywords

  • Mole fraction

  • Concentration term

  • Solution

  • Component

  • Moles

  • Dimensionless

  • Raoult's Law

Practice preview

  • If the mole fraction of a non-volatile solute in an aqueous solution is 0.1, what is the mole fraction of water?…

    medium

  • A solution contains 2 moles of ethanol and 8 moles of water. If the density of water is 1 g/mL and the molar mass of ethanol is 46 g/mol, what is the mole fraction of ethanol?…

    medium

  • In a solution of two components A and B, if the mole fraction of A (x_A) is 0.4, what is the mole fraction of B (x_B)?…

    easy

Practice 8 questions