Chemistry
Chemistry in the FMRDA Medicine Admission exam tests the mole concept and stoichiometry, gas behaviour, chemical equilibrium, acid–base chemistry, and the structure and reactions of organic functional groups. Numerical items dominate, so unit tracking and clear mole reasoning matter more than memorised equations.
Stoichiometry and gases
Balance equations before using mole ratios. Convert mass to moles with n = m/M; convert solution volume to moles with n = cV, where V is in litres. For gases, PV = nRT uses kelvin and litres; at STP, 1 mol occupies 22.4 L. A limiting reagent is the reactant that produces the least product, not simply the reactant with the smallest mass.
Equilibrium and acids
Le Chatelier's principle predicts the direction of shift after changes in concentration, pressure, or temperature. Kc and Kp depend only on temperature. For weak acids, Ka = [H+][A−]/[HA] and pH = −log[H+]. Strong acids dissociate completely; weak acids only partially. A buffer resists pH change because it contains a weak acid and its conjugate base.
Organic chemistry
Identify functional groups: alcohols (OH), aldehydes (CHO), ketones (C=O within a chain), carboxylic acids (COOH), esters (COO), amines (NH2), and amides (CONH2). Primary alcohols oxidise to aldehydes and then carboxylic acids; secondary alcohols to ketones; tertiary alcohols resist oxidation. Addition reactions occur at C=C; substitution is typical of alkanes and benzene.
Worked example
10.0 g of CaCO3 (M = 100 g/mol) reacts with 100 mL of 1.0 M HCl: CaCO3 + 2HCl → CaCl2 + CO2 + H2O. n(CaCO3) = 0.100 mol; n(HCl) = 0.100 mol. Complete reaction of the carbonate needs 0.200 mol HCl, so HCl is limiting. n(CO2) = 0.100/2 = 0.050 mol. Volume at STP = 0.050 × 22.4 = 1.12 L.
Traps that cost marks
- Forgetting to convert mL to L when using cV.
- Treating the smallest-mass reactant as limiting without checking mole ratios.
- Using Celsius in gas-law calculations.
- Including solids or pure liquids in equilibrium expressions.
- Confusing pH with pKa when judging acid strength.