Chemists answer questions by carrying out a scientific investigation: an organised way of testing ideas through experiment. Following clear steps makes the results reliable and repeatable.
Steps of a scientific investigation
- Identify the problem — ask a question that can be tested.
- Make a hypothesis — a testable statement predicting the outcome.
- Identify variables — manipulated, responding and fixed (controlled).
- Plan and carry out the experiment — collect data safely.
- Record and analyse data — use tables and graphs.
- Draw a conclusion — accept or reject the hypothesis.
Types of variables
| Variable | Meaning |
|---|---|
| Manipulated | The factor you change on purpose |
| Responding | The factor you measure as the result |
| Fixed (controlled) | Factors kept constant for a fair test |
Key idea / 要点
A fair test changes only the manipulated variable while keeping all fixed variables constant, so any change in the responding variable is caused by the manipulated variable alone.
Worked example / 例题
Investigation: "Does temperature affect how fast a reaction occurs?"
Manipulated variable: temperature of the acid.
Responding variable: time for the reaction to finish.
Fixed variables: volume and concentration of acid, mass and size of the solid.
Hypothesis: the higher the temperature, the shorter the time (faster reaction).
Reliable and accurate results
To improve reliability, repeat readings and take an average. To improve accuracy, use suitable apparatus and read scales at eye level. A well-planned investigation lets other people repeat the work and get the same result. We should also distinguish an observation, which is what we notice using our senses or instruments, from an inference, which is a reasonable explanation of that observation. Presenting data clearly in tables and graphs makes patterns easier to see and helps us defend the conclusion we finally reach.
Remember / 记住
- A hypothesis must be testable.
- Only one variable is manipulated at a time.
- Repeat readings to check reliability.