Overview
This lecture covers key multiple-choice questions from Class 11 Chemistry Chapter 1, focusing on basic concepts such as measurement units, mole concept, stoichiometry, gas laws, and chemical equations.
Measurement and Units
- SI base units include meter (length), kilogram (mass), and kelvin (temperature); pound is not an SI unit.
- The SI unit of temperature is kelvin (K).
- The SI unit of the amount of substance is the mole.
- Significant figures in 0.00345 are four.
Mole Concept and Calculations
- Avogadro’s number is 6.022 × 10²³ particles per mole.
- The mass of 1 mole of a substance is called its molar mass.
- The molar mass of H₂O is 18 g/mol.
- Formula mass is in grams per mole.
- The number of atoms in 1 mole equals Avogadro’s number.
Chemical Formulas and Equations
- Empirical formula shows the simplest whole-number ratio of atoms in a compound.
- Molecular formula can be the same as or a multiple of the empirical formula.
- Example: C₆H₁₂O₆ (glucose) has empirical formula CH₂O.
- Balanced water formation: 2H₂ + O₂ → 2H₂O.
- CH₄ combustion: CH₄ + 2O₂ → CO₂ + 2H₂O.
- CaCO₃ reaction: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O.
Stoichiometry and Types of Reactions
- Stoichiometry studies the quantitative relationships in chemical reactions.
- Limiting reactant is the one completely consumed first, determining product amount.
- Synthesis, decomposition, and combustion are types of chemical reactions; fusion is not.
Gases and Gas Laws
- Boyle’s law: pressure and volume are inversely related (P∝1/V).
- SI unit of pressure is pascal (Pa).
- Ideal gas law: PV = nRT.
- One mole of ideal gas occupies 22.4 L at STP.
- Dalton’s law: total pressure equals sum of partial pressures.
Solutions and Colligative Properties
- Colligative properties include boiling point elevation, freezing point depression, and vapor pressure lowering.
- Raoult’s law: vapor pressure of a solution depends on solute concentration.
- Molarity is moles of solute per liter; 0.5 mol in 250 mL = 2 mol/L.
Miscellaneous
- Distillation removes impurities by vaporizing and condensing the solvent.
- Mass percent of carbon in CO₂ is 50%.
- Percentage composition: (mass of each element/total mass) × 100.
Key Terms & Definitions
- Mole — SI unit for amount of substance, contains Avogadro’s number of particles.
- Empirical formula — simplest whole-number ratio of atoms in a compound.
- Molar mass — mass of one mole of a substance (g/mol).
- Stoichiometry — calculation of reactants and products in chemical reactions.
- Limiting reactant — reactant that is used up first in a chemical reaction.
- Colligative property — property of solutions depending on solute particle number, not type.
Action Items / Next Steps
- Review types of chemical reactions and practice writing balanced equations.
- Practice calculations using the ideal gas law and molarity.
- Memorize key SI units and important definitions for exams.