In Class 12 chemistry, a non-ideal solution refers to a mixture of two or more components that deviates from ideal behavior and does not follow Raoult’s law over the entire range of composition. Non-ideal solutions exhibit various phenomena and properties that differ from those observed in ideal solutions.

Here are key points about non-ideal solutions in Class 12 chemistry:

1. Deviations from Raoult’s Law: Non-ideal solutions exhibit deviations from Raoult’s law, which states that the partial vapor pressure of a component in the solution is directly proportional to its mole fraction in the solution. These deviations can be positive or negative.
2. Positive Deviations: Positive deviations occur when the observed vapor pressure of a component is higher than predicted by Raoult’s law. Positive deviations are typically observed in mixtures where the intermolecular forces between the components are weaker than the forces within the pure components. This can lead to enhanced vapor pressure and volatility.
3. Negative Deviations: Negative deviations occur when the observed vapor pressure of a component is lower than predicted by Raoult’s law. Negative deviations are typically observed in mixtures where the intermolecular forces between the components are stronger than the forces within the pure components. This can result in reduced vapor pressure and lower volatility.
4. Azeotropes: Azeotropes are special types of non-ideal solutions that exhibit constant boiling points. An azeotrope is a mixture with a composition that distills at a constant temperature, indicating that the vapor and liquid phases have the same composition. Azeotropic mixtures cannot be separated into their pure components by simple distillation.
5. Activity Coefficients: In non-ideal solutions, the activity coefficients of the components are introduced to account for deviations from ideality. Activity coefficients are dimensionless values that quantify the deviation from Raoult’s law. They are used to adjust the ideal behavior assumptions and calculate the actual vapor pressures, concentrations, and other properties.
6. Excess Properties: Non-ideal solutions exhibit excess properties, such as excess enthalpy, excess entropy, and excess volume. These properties arise due to the differences in intermolecular interactions between the components compared to the pure components.
7. Real-World Examples: Non-ideal solutions are commonly encountered in various real-world systems, including mixtures of liquids, liquid solutions of solids, and solutions of volatile compounds. For example, ethanol and water form a non-ideal solution due to the differences in intermolecular forces.

Understanding the behavior of non-ideal solutions is crucial in many areas of chemistry, such as thermodynamics, phase equilibria, and chemical process design. Experimental measurements and theoretical models are employed to study and describe the behavior of non-ideal solutions in greater detail.