Scientific Skills and Investigation
What this domain tests
Scientific Skills and Investigation examines how you plan, carry out, record and evaluate an experiment. SPM questions ask you to identify variables, state a hypothesis, tabulate data, plot graphs and draw conclusions supported by evidence, not opinion.
Core rules
- An observation is what you detect with senses or instruments; an inference is a logical explanation of it.
- A hypothesis is a testable statement linking manipulated and responding variables, for example: 'The rate of reaction increases when temperature increases.'
- The manipulated variable is changed, the responding variable is measured, and fixed variables are kept constant.
- Accuracy is closeness to the true value; precision is closeness of repeated readings; sensitivity is the smallest change an instrument detects.
- Use SI units: m, kg, s, A, K, mol, cd. Record to the instrument's precision and include units in tables and axes.
Worked example
A student investigates how the concentration of hydrochloric acid affects the rate of reaction with marble chips. The manipulated variable is acid concentration; the responding variable is the volume of gas collected per unit time; fixed variables include temperature and the mass and size of marble chips. The hypothesis is: 'As acid concentration increases, the rate of gas production increases.' The student measures 20 cm³ of gas with a syringe every 30 s and plots volume against time. The initial gradient of the graph is the rate.
Traps
Do not write an inference as an observation. Do not omit fixed variables. Do not connect anomalous points blindly; circle and explain them. When calculating gradients, use a tangent on a curve, not two distant points.