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CBSE Class 12 Chemistry: Full Revision of Solutions, Electrochemistry & Chemical Kinetics

H2: Session Start & Motivation After Physics Exam

  • Instructor's Message: The session begins by addressing students who found the Physics paper difficult. The instructor motivates the class, stating that there's no need for worry as checking will likely be lenient.
  • Action Plan: The focus is now entirely on Chemistry to compensate for any lost marks.
  • Strategy: Focus on NCERT Exemplar, Competency-Based Questions, and revision of previous year questions.

H2: Chapter 1 - Solutions

This chapter is summarized with a focus on key formulas and theory. For a strong foundation, you can review the basic concepts of matter in this Comprehensive Chemistry Review: Isotopes, Ionic Compounds, and Molar Mass.

H3: Basic Concepts & Concentration Terms

  • Solution: Homogeneous mixture of solute (minor component) and solvent (major component).
  • Concentration Methods:
    • Mass Percentage: (Mass of solute / Mass of solution) × 100
    • Volume Percentage: (Volume of solute / Volume of solution) × 100
    • Parts Per Million (ppm): For very dilute solutions.
    • Mole Fraction (x): Ratio of moles of a component to total moles.
    • Molarity (M): Moles of solute / Volume of solution (L) – depends on temperature.
    • Molality (m): Moles of solute / Mass of solvent (kg) – does not depend on temperature.

H3: Henry's Law

  • Statement: The mass of a gas dissolved in a liquid at a given temperature is directly proportional to its pressure.
  • Formula: p = KH × x (where p is partial pressure, KH is Henry's constant, x is mole fraction).
  • Key Points:
    • KH is dependent on the nature of the gas and temperature.
    • Solubility ∝ 1/KH (Higher KH means lower solubility).
    • Temperature Increase → KH increases → Solubility decreases.
  • Applications: Scuba diving (use of He), mountain climbing, packing cold drinks.

H3: Raoult's Law & Ideal/Non-Ideal Solutions

  • Raoult's Law: For a solution of volatile liquids, partial pressure of each component is directly proportional to its mole fraction.
  • Ideal Solutions: Obey Raoult's Law at all concentrations; ΔHmix = 0, ΔVmix = 0.
  • Non-Ideal Solutions: Show deviations from Raoult's Law.
    • Positive Deviation: A–B interactions weaker than A–A/B–B. ΔHmix > 0, ΔVmix > 0. (e.g., Ethanol + Cyclohexane)
    • Negative Deviation: A–B interactions stronger. ΔHmix < 0, ΔVmix < 0. (e.g., Acetone + Chloroform)
  • Azeotropes: Mixtures with a constant boiling point that cannot be separated by distillation.
    • Minimum Boiling Azeotropes: Show positive deviation (e.g., 95% Ethanol + 5% Water).
    • Maximum Boiling Azeotropes: Show negative deviation.

H3: Colligative Properties

  • Properties dependent on the number of solute particles, not their nature.
  1. Relative Lowering of Vapour Pressure: (P0 - P)/P0 = x2 (mole fraction of solute).
  2. Elevation in Boiling Point: ΔTb = Kb × m
  3. Depression in Freezing Point: ΔTf = Kf × m (Application: Adding salt to melt ice on roads).
  4. Osmotic Pressure (π): π = iCRT. This is considered the best colligative property for determining molar mass as it's measurable at room temperature.
    • Hypertonic/Hypotonic/Isotonic: Solutions with high/low/equal osmotic pressure.

H3: Abnormal Molar Mass & van't Hoff Factor (i)

  • Van't Hoff Factor (i): Accounts for dissociation or association of solute.
    • i = (Actual number of particles) / (Number of particles expected if no dissociation)
  • Modified Colligative Property Formulas: ΔTb = i Kb m; π = i CRT
  • Example: For KCl solution, if 100% dissociated, i = 2.

H2: Chapter 2 - Electrochemistry

H3: Electrolytic Cells vs. Galvanic Cells

  • Electrolytic Cell: Converts electrical energy into chemical energy (non-spontaneous). Anode (+), Cathode (-).
  • Galvanic/Voltaic Cell: Converts chemical energy into electrical energy (spontaneous). Anode (-), Cathode (+).

H3: Standard Electrode Potential & Nernst Equation

  • Standard Hydrogen Electrode (SHE): Assigned a potential of 0 V. Used as reference for other electrodes.
  • Nernst Equation: Relates cell potential (Ecell) to concentration and temperature.
    • At 298 K: Ecell = E°cell - (0.0591/n) log Q (where Q is reaction quotient).
  • Spontaneity: A reaction is spontaneous if Ecell is positive (ΔG is negative).

H3: Conductance & Kohlrausch's Law

  • Conductivity (κ): Inverse of resistivity; specific conductivity of a solution.
  • Molar Conductivity (Λm): Λm = (κ × 1000) / Molarity
  • Kohlrausch's Law: At infinite dilution, molar conductivity is the sum of contributions from individual ions: Λ°m = λ°+ + λ°-
  • Application: Determine dissociation constant (Ka) and degree of dissociation (α).

H3: Faraday's Laws of Electrolysis

  1. First Law: Mass deposited (m) ∝ Charge passed (Q). m = ZIt (Z is electrochemical equivalent).
  2. Second Law: When same charge is passed through different electrolytes, masses of substances liberated are proportional to their equivalent masses.

H3: Batteries & Corrosion

  • Primary Batteries: Not rechargeable (e.g., Dry Cell, Mercury Cell).
    • Mercury Cell: Provides a constant potential of ~1.35 V.
  • Secondary Batteries: Rechargeable (e.g., Lead storage battery, Ni-Cd).
  • Fuel Cell: Converts chemical energy from fuel into electricity (e.g., H2-O2 fuel cell used in Apollo program).
  • Corrosion: Prevention methods include painting, galvanization, and sacrificial protection.

H2: Chapter 3 - Chemical Kinetics

H3: Rate of Reaction

  • Average Rate: Change in concentration over a time interval.
  • Instantaneous Rate: Rate at a specific moment (calculated from the slope of the concentration vs time graph).
  • Rate Law: r = k [A]x[B]y (x and y are reaction orders).

H3: Order of Reaction & Integrated Rate Laws

  • Zero Order Reaction: Rate independent of concentration.
    • Integrated Rate: [A] = [A]0 - kt
    • Half-Life (t1/2): t1/2 = [A]0 / 2k
  • First Order Reaction: Rate ∝ [A].
    • Integrated Rate: t = (2.303/k) log([R]0/[R])
    • Half-Life (t1/2): t1/2 = 0.693/k (Independent of initial concentration).
    • All radioactive decays are first order.

H3: Pseudo First Order Reactions

  • A reaction that appears to be higher order but follows first-order kinetics under conditions where one reactant is in large excess (e.g., hydrolysis of ester in acidic medium).

H3: Activation Energy & Arrhenius Equation

  • Activation Energy (Ea): Minimum extra energy required by reactants to form the activated complex.
  • Arrhenius Equation: k = A e-Ea/RT
  • Log form: log(k2/k1) = (Ea/2.303R)(1/T1 - 1/T2)
  • Effect of Catalyst: Lowers activation energy, speeding up the reaction.

For additional high-yield topics and practice problems, check out the Class 12 Physics: Introduction to Electrostatics and Electric Charges guide. To further strengthen your chemistry understanding, you can also refer to the Comprehensive Overview of Current Electricity for NEET 2025 resource. Finally, for exam strategy and to see how these concepts are applied, take a look at the Class 11 Physics GK Board Exam: Complete Guide with Last Year Topper PDF. For biology integration, see Human Reproduction Class 12: Complete Chapter with Diagrams and MCQs.

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