Chemistry: Structure, Reactions, and Calculation Discipline
What the Kankor chemistry section rewards
Chemistry items span atomic structure, the periodic table, chemical bonding, stoichiometry, gases, solutions, acids and bases, oxidation–reduction, and introductory organic chemistry. Many questions are quantitative; others test definitions and trends.
Concepts you must own
- Atomic structure: protons, neutrons, electrons; isotopes; electron configuration and its link to group and period.
- Periodic trends: atomic radius decreases across a period and increases down a group; electronegativity and ionization energy follow the opposite pattern.
- Bonding: ionic versus covalent, polarity, and intermolecular forces.
- Mole concept: n = m/M; Avogadro's number; molar volume of a gas at STP.
- Stoichiometry: balanced equations give mole ratios; identify the limiting reactant.
- Solutions: molarity M = moles of solute / liters of solution.
- Acids and bases: pH = −log[H⁺]; neutralization stoichiometry.
- Redox: oxidation is loss of electrons; assign oxidation numbers systematically.
Traps that appear
- Unbalanced equations before doing mole ratios.
- Confusing molarity with molality and forgetting to convert mL to L.
- Limiting-reactant problems where the obvious reagent is not limiting.
- pH and [H⁺] conversions - pH 3 means 10⁻³ M, not 3 M.
- Periodic trend direction questions phrased as "which has the larger…".
Rule of thumb
For any calculation, convert mass to moles first, use the balanced equation's ratio, then convert back to the requested unit. Worked example: how many grams of water form when 4 g of H₂ reacts completely with oxygen? Moles H₂ = 4/2 = 2 mol. From 2H₂ + O₂ → 2H₂O, the ratio is 1:1, so 2 mol H₂O form. Mass = 2 × 18 = 36 g.