What is the unit of Mole fraction? 

Hint: To understand the unit of mole fraction, we first need to define what mole fraction means. Mole fraction is the ratio of the number of moles of a specific component to the total number of moles in a mixture. It is a convenient way to express the concentration of a solution. Simply put, mole fraction refers to the total quantity of a particular component in moles, divided by the total number of moles of all components in the mixture. This quantity is sometimes referred to as the "amount fraction."

In mathematical terms, the mole fraction, denoted by X, is calculated as:

Mole Fraction of Component A = 
(Moles of Component A) / (Total Moles in the Mixture)

For a solution containing two components, A and B, the mole fraction of A can be expressed as:

Mole Fraction of A (XA) = nA / (nA + nB) 

Here, n_A and n_B represent the number of moles of components A and B, respectively.

Key Characteristics of Mole Fraction

• Mole fraction is a dimensionless quantity since it is the ratio of two similar quantities (moles).
• The total mole fraction of all components in a mixture always equals one.
• Unlike molarity (moles per liter) or molality (moles per kilogram), mole fraction does not depend on the volume or mass of the solution, making it ideal for phase diagrams and thermodynamic calculations.

Why Mole Fraction Has No Unit

Since mole fraction is a ratio of moles to moles, the units cancel out, leaving it without any dimension. Therefore, mole fraction is always represented as a pure number, without any unit.

Misconceptions About Mole Fraction

Options such as "mole/liter" or "mole-kilogram" are incorrect because they represent units for molarity and molality, respectively. Mole fraction is neither of these. It is simply a dimensionless ratio.

Applications of Mole Fraction

Mole fraction is widely used in various scientific fields, especially in:

• Constructing phase diagrams.
• Calculating partial pressures in gas mixtures using Dalton's Law.
• Understanding thermodynamic properties of solutions.

Conclusion

The correct answer is that mole fraction is dimensionless. It is an essential concept in chemistry, providing a reliable and unitless way to express the composition of a mixture.