Chemistry - Mole Concept, Equilibrium and Organic Basics
What the paper tests
Chemistry in the IOE entrance mixes short numericals with recall of structure and trends. The numerical core is the mole concept, concentration, gas laws, thermochemistry, ionic equilibrium and electrochemistry. The recall core is atomic structure and periodic trends, chemical bonding and VSEPR shape, coordination compounds, s- and p-block chemistry, environmental chemistry, and organic chemistry - nomenclature, isomerism, and the reactions of hydrocarbons and their functional-group derivatives.
Core rules
- Mole concept: moles = mass/molar mass = molecules/6.022 × 10²³ = volume at STP/22.4 L.
- Concentration: molarity = moles of solute per litre of solution; dilution obeys M₁V₁ = M₂V₂.
- Gas laws: PV = nRT with T in kelvin; at STP one mole of an ideal gas occupies 22.4 L.
- Equilibrium: Le Chatelier shifts the position on changes of concentration, pressure or temperature; Kp = Kc(RT)^Δn.
- pH: pH = −log[H⁺]; a strong monobasic acid at 0.1 M gives pH = 1.
- Organic: IUPAC longest-chain naming, Markovnikov addition to alkenes, and the standard tests - Tollens and Fehling for aldehydes, iodoform for methyl ketones, bromine water for unsaturation.
Worked example
0.365 g of HCl is dissolved to make 100 mL of solution. Molar mass of HCl = 36.5 g/mol, so moles = 0.365/36.5 = 0.01 mol. Molarity = 0.01 mol / 0.100 L = 0.1 M. Since HCl is a strong monobasic acid, [H⁺] = 0.1 M and pH = −log(0.1) = 1.0.
Traps that cost marks
- Using the solvent volume instead of the solution volume when computing molarity.
- Forgetting to identify the limiting reagent before calculating product yield.
- Treating a weak acid as fully dissociated, then reporting an impossibly low pH.
- Mixing up ortho, meta and para positions, or cis and trans isomers.
- Reversing periodic trends: atomic radius decreases and electronegativity increases across a period.