Raoult’s Law and Deviations

Binary Liquid Solutions

• In a binary liquid solution where both components are volatile, the total pressure is calculated using Raoult's law.

Deviations from Raoult's Law

• Positive deviations from Raoult's law are observed in solutions where the intermolecular forces between the components are weaker than the forces between the same molecules.
• Negative deviations from Raoult's law are observed in solutions where the intermolecular forces between the components are stronger than the forces between the same molecules.

Properties of Solutions

• The properties of solutions that depend on the number of solute particles regardless of their chemical identity are colligative properties.

Osmotic Pressure

• Applying a pressure higher than the osmotic pressure to a solution can reverse the process of osmosis.

Henry's Law

• According to Henry's law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas.

Vapor Pressure of a Solvent

• The vapor pressure of a solvent is lowered by a non-volatile solute according to Raoult's law.

Negative Deviations from Raoult's Law

• Mixtures like phenol and aniline show negative deviations from Raoult's law because of the formation of hydrogen bonds between the components.
• The characteristic of a mixture that leads to negative deviations from Raoult's law is the formation of strong intermolecular forces between the components.

Azeotrope Formation

• Solutions showing large positive deviations from Raoult's law form a minimum boiling azeotrope.

Hydrogen Bonds and Vapor Pressure

• The formation of hydrogen bonds between chloroform and acetone reduces their vapor pressures.
• The main reason behind the negative deviations from Raoult's law in mixtures like chloroform and acetone is the formation of hydrogen bonds between the components.

Binary Mixtures

• A binary mixture with the same composition in both liquid and vapor phases is called a zeotrope.

Positive Deviations from Raoult's Law

• A solution shows positive deviation from Raoult's law when the intermolecular forces between the components are weaker than the forces between the same molecules.
• Adding acetone to pure ethanol disrupts the hydrogen bonds between the ethanol molecules, increasing the vapor pressure.
• In a solution showing positive deviation, the vapor pressure is higher than that of the pure solvent.
• The interaction that is weaker in a solution showing positive deviation from Raoult's law is the intermolecular force between the components.

Dipolar Interactions

• Adding carbon disulphide to acetone disrupts the dipolar interactions between the acetone molecules, increasing the vapor pressure.

Laws Associated with Deviations

• Raoult's law is associated with deviations such as positive and negative deviation from ideal behavior in solutions.

Explore the concept of deviations from Raoult's law in solutions, focusing on the nature of molecular interactions and the implications of positive deviations. Learn how weaker solute-solvent interactions lead to increased vapor pressure in such solutions.