Science subjects (Physics, Chemistry, Biology)
STPM Physics, Chemistry and Biology test core theory, data analysis and practical reasoning. Each subject has written papers plus a practical or school-based assessment component, so you must be able to describe apparatus, control variables and interpret readings as well as write essays.
Core concepts
- Physics: SI units and dimensions; Newton's laws and conservation of momentum; circuits and Kirchhoff's laws; wave interference; electric and magnetic fields.
- Chemistry: mole concept and stoichiometry; equilibria and pH; thermochemistry; organic functional groups and mechanisms; titration calculations.
- Biology: cell ultrastructure; enzymes and factors affecting rate; mitosis and meiosis; genetics and DNA; transport and ecology.
Worked example
25.0 cm³ of 0.100 mol dm⁻³ HCl is neutralised by 0.0500 mol dm⁻³ NaOH. What volume of NaOH is needed? The equation is HCl + NaOH → NaCl + H₂O, so the mole ratio is 1:1. n(HCl) = 0.100 × 25.0/1000 = 2.50 × 10⁻³ mol. Therefore n(NaOH) = 2.50 × 10⁻³ mol. V(NaOH) = n/c = 2.50 × 10⁻³ / 0.0500 = 0.0500 dm³ = 50.0 cm³. The reasoning mark is for the ratio and the cm³-to-dm³ conversion.
Traps
Forgetting to convert cm³ to dm³; unbalanced equations; using the wrong mole ratio; not giving units; in physics, ignoring direction in vector quantities; in biology, confusing mitosis with meiosis or describing enzymes as 'used up'.