Definition:
Mole fraction (X) is defined as the ratio of the number of moles of a particular component to the total number of moles of all components in a solution. It is a unitless quantity and is used in various thermodynamic calculations, such as vapor pressure, colligative properties, and gas mixtures.
Formula:
For a solution containing solute and solvent, the mole fraction of each component is given by:
Example Calculation:
A solution is prepared by dissolving 20 g of NaCl in 180 g of water. Calculate the mole fraction of NaCl and water.
Solution:
Answer:
- Mole fraction of NaCl = 0.033
- Mole fraction of Hâ‚‚O = 0.967
Advantages of Mole Fraction:
- Temperature Independent: Since mole fraction is a ratio, it does not change with temperature variations.
- Useful in Gas Laws: Ideal for calculating partial pressures in gas mixtures using Dalton’s Law.
- Colligative Properties: Used in Raoult’s Law to determine vapor pressure lowering and freezing point depression.
Factors Affecting Mole Fraction (χ)
Several factors influence mole fraction, which are listed below:
1. Amount of Components (Solute & Solvent)
- Increasing the moles of a component increases its mole fraction while decreasing the mole fraction of the other component.
- Decreasing the moles of a component lowers its mole fraction.
2. Total Number of Moles in Solution
- Mole fraction depends on the ratio of individual component moles to the total moles in the solution.
3. Nature of the Components
- Volatile components may change mole fractions due to evaporation.
- Highly soluble solutes increase their mole fraction in solution.
4. Temperature
- Affects solubility and, consequently, the mole fraction of solutes in solution.
- Higher temperatures may increase or decrease the mole fraction depending on the solubility characteristics of the solute.
Applications in Pharmaceuticals:
- Drug Formulation: Helps in solvent-solute interactions and determining the ideal mixing ratio of drugs and excipients.
- Gas Mixtures: Important in inhalation therapy (e.g., oxygen-nitrogen mixtures).
- Osmotic Pressure Calculations: Used in understanding the behavior of biological fluids and IV solutions.
Conclusion:
Mole fraction is a fundamental concentration unit in chemistry and pharmaceutical sciences. It is particularly useful in gas mixtures, colligative properties, and drug formulation studies. Since it remains constant with temperature, it is widely used in thermodynamic and equilibrium calculations.
Also, read this: What is Molarity