Frequently Asked Question

## Molarity and Mole Fraction: A Chemistry Perspective
Molarity (M):

Definition: Molarity is the concentration of a solution expressed as the number of moles of solute per liter of solution.
Formula: Molarity (M) = moles of solute / liters of solution
Example 1: Calculating Molarity

You dissolve 0.5 moles of sodium chloride (NaCl) in 2 liters of water.
Molarity (M) = 0.5 moles / 2 liters = 0.25 M
Example 2: Determining the Moles of Solute

You have a 1.5 M solution of hydrochloric acid (HCl) and need 0.75 moles of HCl.
Moles of solute = Molarity (M) × Liters of solution
0.75 moles = 1.5 M × Liters of solution
Liters of solution = 0.75 moles / 1.5 M = 0.5 liters
Mole Fraction (χ):

Definition: Mole fraction represents the ratio of the number of moles of a specific component to the total number of moles in a mixture.
Formula: Mole fraction (χ) = moles of component / total moles in mixture
Example 1: Calculating Mole Fraction

You have a mixture containing 2 moles of ethanol (C2H5OH) and 3 moles of water (H2O).
Mole fraction of ethanol (χethanol) = 2 moles / (2 moles + 3 moles) = 0.4
Mole fraction of water (χwater) = 3 moles / (2 moles + 3 moles) = 0.6
Note: The sum of mole fractions of all components in a mixture always equals 1.
Conversion:

You can't directly convert molarity to mole fraction without knowing the density of the solution.
However, you can calculate mole fraction if you know the molarity and the density of the solution, as you can then determine the mass of the solute and solvent.
Key Points:

Molarity is a convenient measure for expressing solution concentrations in chemistry.
Mole fraction is a useful concept for understanding the composition of mixtures and for calculating vapor pressures and other properties.