Define mole fraction.

The mole fraction definition refers to the ratio of the number of moles of a particular component to the total number of moles of all components in a mixture. It is a way to express the concentration of a substance in a solution or mixture in a dimensionless form.

Explanation:

The mole fraction is usually represented by the symbol X, and it is calculated using the formula:

X_A = (Moles of component A) / (Total moles of all components in the mixture)

• X_A represents the mole fraction of component A.
• The numerator is the number of moles of the specific component (e.g., solute or solvent).
• The denominator is the total number of moles of all components in the mixture, including solutes and solvents.

Key Points:

1. Dimensionless Quantity: The mole fraction has no unit because it is a ratio of similar quantities (moles).
2. Sum of Mole Fractions: In any mixture, the sum of the mole fractions of all components always equals 1. For example: 
   X_A + X_B + X_C + ... = 1
   where X_A, X_B, X_C, etc., are the mole fractions of different components in the mixture.

Practical Use:

The mole fraction definition is crucial in chemistry, especially in the study of solutions and gases. It is used in Raoult's law, Dalton’s law of partial pressures, and other calculations to describe the composition of mixtures.

For example, in a mixture of oxygen and nitrogen gases, if the mole fraction of oxygen is 0.25, it means oxygen makes up 25% of the mixture in terms of moles.