General Scientific Knowledge and Aptitude
This paper checks whether you can apply school- and degree-level science across disciplines - physics, chemistry, biology and earth science - and handle numerical, verbal and logical reasoning quickly. Expect SI-unit handling, graph and table interpretation, basic stoichiometry, electricity and mechanics, cell biology and ecology, plus aptitude items on ratios, percentages and number series.
Core rules and concepts
- Convert to base SI units before calculating: 1 L = 10⁻³ m³; 1 mg = 10⁻³ g = 10⁻⁶ kg; in dilute aqueous solution 1 ppm ≈ 1 mg/kg ≈ 1 mg/L.
- Moles: n = m/M = cV. At standard temperature and pressure one mole of an ideal gas occupies about 22.4 L.
- Dilution and mixing obey c₁V₁ = c₂V₂; percentage concentration may be w/v, w/w or v/v and the three are not interchangeable.
- Electrical relations: V = IR, P = VI; energy in kWh = power in kW × time in hours.
- Read every graph from its axis labels and stated units before choosing an option.
Worked example
250 mL of 0.20 mol/L NaCl solution is diluted to 1.00 L. Find the Na⁺ concentration in mg/L. c₂ = c₁V₁/V₂ = (0.20 mol/L × 0.250 L) / 1.00 L = 0.050 mol/L. Na⁺ per litre = 0.050 mol × 23 g/mol = 1.15 g = 1150 mg/L. Check: a four-fold dilution must quarter the concentration, and 0.20 → 0.050 does exactly that.
Traps that cost marks
- Confusing µg with mg, or assuming ppm equals mg/L when the density is not 1.
- Reporting more significant figures than the input data supports.
- Reading the mass of NaCl when the question asks for Na⁺ only (using 58.5 g/mol instead of 23 g/mol would give 2925 mg/L).
- Mixing mass percent with mass/volume percent in concentration questions.