Summary
NCERT Class 12 Chemistry Chapter 1 covers Solutions — homogeneous mixtures of two or more substances — including types of solutions, concentration units, Henry's law, Raoult's law, colligative properties (vapour pressure lowering, boiling point elevation, freezing point depression, osmotic pressure), and van't Hoff factor for solutes that associate or dissociate.
Chapter 1 of NCERT Class 12 Chemistry Part I introduces solutions as homogeneous mixtures where the component present in the largest quantity is the solvent. It covers nine types of solutions (gaseous, liquid, and solid) and seven concentration units including molarity, molality, mole fraction, and parts per million. Henry's law governs gas solubility in liquids, while Raoult's law describes vapour pressure of liquid solutions. The chapter explains ideal versus non-ideal solutions, azeotropes, and four colligative properties used to determine molar masses of solutes. The van't Hoff factor accounts for ionic dissociation or molecular association in solution.
Key points & formulas
- 01Solutions are homogeneous mixtures; the component in largest quantity is the solvent, and concentration units include molarity (mol/L), molality (mol/kg), mole fraction, mass percentage, and ppm
- 02Henry's law states that at constant temperature the solubility of a gas in a liquid is directly proportional to its partial pressure above the liquid (p = KH x)
- 03Raoult's law states that the partial vapour pressure of each volatile component equals its mole fraction multiplied by its vapour pressure in the pure state (p1 = x1 p1°)
- 04Ideal solutions obey Raoult's law over the entire concentration range with zero enthalpy and volume of mixing; non-ideal solutions show positive or negative deviations and can form azeotropes
- 05Colligative properties — relative lowering of vapour pressure, elevation of boiling point (DTb = Kb m), depression of freezing point (DTf = Kf m), and osmotic pressure (P = CRT) — depend only on the number of solute particles, not their identity
- 06The van't Hoff factor i corrects colligative property equations for electrolytes that dissociate (i > 1) or molecules that associate (i < 1) in solution
Frequently asked questions
01What is Henry's law and where is it applied in Class 12 Chemistry Chapter 1?
Henry's law states that at a constant temperature the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid, expressed as p = KH x, where KH is the Henry's law constant. It explains why CO2 is dissolved under high pressure in soda water, why scuba divers risk 'bends' when ascending rapidly, and why oxygen concentration in blood decreases at high altitudes.
02What are colligative properties and which four are discussed in this chapter?
Colligative properties depend on the number of solute particles in a solution, not on the chemical identity of the solute. The four colligative properties covered are: (1) relative lowering of vapour pressure, (2) elevation of boiling point, (3) depression of freezing point, and (4) osmotic pressure. They are used experimentally to determine molar masses of solutes including proteins and polymers.
03What is the van't Hoff factor and why does it matter for electrolytes?
The van't Hoff factor i is defined as the ratio of the normal molar mass to the experimentally determined (abnormal) molar mass, or equivalently the ratio of the observed colligative property to the calculated colligative property. For electrolytes that dissociate into ions (e.g., KCl gives i ≈ 2), the measured molar mass is lower than the true value; for molecules that associate (e.g., acetic acid dimerises in benzene giving i ≈ 0.5), it is higher. The modified equations become DTb = i Kb m and P = i n2 RT/V.
04Is the NCERT Class 12 Chemistry Chapter 1 PDF free to download?
Yes, the NCERT Class 12 Chemistry Chapter 1 (Solutions) PDF is completely free to download on cbseprepmaster.com.
More chapters in Chemistry Part I
This is the complete Chemistry Part I Chapter 1 as published by NCERT — every diagram, solved example, and exercise included, free. Browse all CBSE Class 12 textbooks.
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