Class 12 Chemistry - MAHARASHTRA
Solutions
The chapter 'Solutions' in Class 12 Chemistry explores the physical chemistry of homogeneous mixtures, focusing on liquid solutions. Students study different types of solutions, solubility of gases and solids in liquids, and concentration units like molarity, molality, and mole fraction. A major portion covers Colligative Properties—properties that depend on the number of solute particles rather than their nature—including relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure. Understanding van't Hoff factor for abnormal molar masses is crucial. This chapter carries significant weightage in Maharashtra (MSBSHSE) board exams.
Start Learning FreeKey Concepts
Henry's Law
States that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the solution at constant temperature.
Raoult's Law
States that the partial vapour pressure of any volatile component of a solution is equal to the vapour pressure of the pure component multiplied by its mole fraction in the solution.
Colligative Properties
Properties of dilute solutions that depend only upon the number of solute particles and not upon their chemical identity (e.g., osmotic pressure).
Van't Hoff Factor (i)
The ratio of the normal molar mass to the experimental molar mass of the solute, used to account for association or dissociation of solutes.
Ideal and Non-ideal Solutions
Ideal solutions obey Raoult's law over the entire range of concentration, whereas non-ideal solutions show positive or negative deviations from Raoult's law.
Important Formulas
Board Exam Info
In the Maharashtra (MSBSHSE) Class 12 Chemistry board exam, the 'Solutions' chapter typically carries about 4 to 6 marks with options. Common question types include numerical problems on colligative properties, derivation of molar mass from osmotic pressure or boiling point elevation, statements of Henry's and Raoult's laws, and distinctions between ideal and non-ideal solutions.
Frequently Asked Questions
Why do we use the van't Hoff factor in colligative property calculations?
The van't Hoff factor is used when solutes undergo dissociation (like NaCl breaking into Na+ and Cl-) or association in solution, which changes the total number of particles and affects the colligative properties.
What is the difference between molarity and molality?
Molarity is the number of moles of solute dissolved per litre of solution and is temperature-dependent. Molality is the number of moles of solute per kilogram of solvent and is independent of temperature.
What causes positive and negative deviations from Raoult's law?
Positive deviations occur when solute-solvent intermolecular forces are weaker than solute-solute and solvent-solvent forces. Negative deviations occur when solute-solvent forces are stronger.
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