Class 12 Chemistry - RAJASTHAN
Solutions
The chapter 'Solutions' in Class 12 Chemistry for Rajasthan Board (RBSE) explores the homogeneous mixtures of two or more components. Students will learn about different methods to express the concentration of solutions, including mass percentage, molarity, molality, and mole fraction. A major portion is dedicated to the study of vapor pressure of liquid solutions and Raoult's law for volatile and non-volatile solutes. The chapter also covers ideal and non-ideal solutions, positive and negative deviations, colligative properties (such as relative lowering of vapor pressure, elevation in boiling point, depression in freezing point, and osmotic pressure), and abnormal molecular masses using the van't Hoff factor.
Start Learning FreeKey Concepts
Molarity (M) and Molality (m)
Molarity is the number of moles of solute dissolved per liter of solution and is temperature-dependent, while molality is the number of moles of solute per kilogram of solvent and remains independent of temperature.
Raoult's Law
It states that for a solution of volatile liquids, the partial vapor pressure of each component in the solution is directly proportional to its mole fraction present in the solution.
Ideal and Non-Ideal Solutions
Ideal solutions obey Raoult's law over the entire range of concentration with zero enthalpy and volume change of mixing, whereas non-ideal solutions show positive or negative deviations from Raoult's law.
Colligative Properties
Properties of solutions that depend only on the number of solute particles dissolved in a given amount of solvent and not on their chemical nature, such as osmotic pressure and elevation in boiling point.
van't Hoff Factor (i)
A correction factor introduced to account for the extent of association or dissociation of solute particles in solution, defined as the ratio of normal molar mass to the abnormal molar mass.
Important Formulas
Board Exam Info
In the Rajasthan Board (RBSE) Class 12 Chemistry examination, the chapter 'Solutions' typically carries around 4 to 5 marks. Questions frequently include numerical problems based on molarity, molality, Raoult's law, colligative properties, and the van't Hoff factor, alongside short theoretical questions on ideal/non-ideal solutions and definitions.
Frequently Asked Questions
Why is molality preferred over molarity while expressing concentration?
Molality is preferred because it involves the mass of the solvent, which does not change with temperature, whereas molarity involves the volume of the solution, which changes with variations in temperature.
What is the difference between ideal and non-ideal solutions?
Ideal solutions strictly follow Raoult's law at all concentrations and temperatures with ΔH_mix = 0, while non-ideal solutions deviate from Raoult's law and show either positive or negative changes in enthalpy and volume upon mixing.
What are colligative properties and name them?
Colligative properties depend only on the number of solute particles, not their nature. The four colligative properties are relative lowering of vapor pressure, elevation in boiling point, depression in freezing point, and osmotic pressure.
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