MECEE-BL Chemistry: mole logic, equilibrium and functional groups
What the chemistry paper tests
Physical, inorganic and organic chemistry at grade 11–12 level: mole concept and stoichiometry, atomic structure, bonding, equilibrium, thermodynamics, electrochemistry, periodicity, coordination compounds, hydrocarbons, functional groups and biomolecules. Numerical items reward clean unit handling; organic items reward recognition of functional groups and reaction conditions.
Core rules
- One mole contains 6.022 × 10^23 particles and, for a gas at STP, occupies 22.4 L.
- Dilution: C1V1 = C2V2; moles of solute are conserved.
- Le Chatelier: a system at equilibrium shifts to oppose a change in concentration, pressure or temperature.
- pH = −log[H+]; strong acids ionize completely, weak acids only partly.
- Hybridization: sp = linear, sp2 = trigonal planar, sp3 = tetrahedral; aromatic rings need 4n+2 π electrons.
- In organic reactions, mark the nucleophile and leaving group before predicting substitution versus elimination.
Worked example
How many grams of O2 are needed to burn 8.0 g of CH4? The equation is CH4 + 2O2 → CO2 + 2H2O. Moles of CH4 = 8.0/16 = 0.50 mol. Moles of O2 = 2 × 0.50 = 1.0 mol. Mass = 1.0 × 32 = 32 g. The same logic identifies a limiting reagent: compare available moles with the stoichiometric ratio, not with masses.
Traps
Do not use 22.4 L for a gas unless conditions are STP. Do not treat a weak acid as fully ionized. In redox, balance atoms and charge separately. In organic nomenclature, choose the longest chain containing the principal functional group. Distinguish empirical from molecular formula, and cis from trans isomerism.