General and Inorganic Chemistry
What the exam tests
Atomic structure, electron configuration, periodic trends, chemical bonding, the mole and stoichiometric calculations, solutions, and redox and acid–base fundamentals. Calculations are marked for units and significant figures as well as for the number.
Core rules
- Mole: n=m/M; one mole contains N_A≈6.02×10²³ particles; the molar volume of an ideal gas is 22.4 L at STP (0 °C, 1 atm).
- Balanced equations give mole ratios. Find the limiting reagent by dividing each amount by its stoichiometric coefficient; the smallest quotient limits.
- Electron configuration follows the Aufbau order (1s 2s 2p 3s 3p 4s 3d…), with Hund's rule and the Pauli exclusion principle.
- Periodic trends: atomic radius decreases across a period and increases down a group; ionisation energy and electronegativity generally increase across and decrease down.
- Oxidation numbers: free element 0; oxygen usually −2 (but −1 in peroxides); hydrogen +1 with nonmetals and −1 with metals.
- pH=−log[H₃O⁺]; strong acids and bases dissociate completely.
Worked example
5.0 g of CaCO₃ (M=100 g/mol) reacts completely with excess HCl: CaCO₃+2HCl→CaCl₂+CO₂+H₂O. n(CaCO₃)=5.0/100=0.050 mol. The equation gives 1 mol CO₂ per mol CaCO₃, so n(CO₂)=0.050 mol. Volume at STP =0.050×22.4=1.12 L. Mass of CO₂ =0.050×44=2.2 g. The 2:1 HCl ratio means 0.10 mol HCl is consumed.
Traps
- Using an unbalanced equation for the mole ratio.
- Continuing the calculation with the excess reagent instead of the limiting reagent.
- Using 22.4 L/mol at room temperature (about 24 L/mol is closer at 25 °C).
- Reporting too many significant figures from a 5.0 g measurement.
- Assigning oxygen −2 in H₂O₂ without checking the peroxide exception.