An observation records what happened. An explanation says why it happened. In Additional Science answers, each one needs its own sentence and its own marks.
This lesson is part of SPM subjects and learning resources. The next lesson, interpreting a small evidence table, shows what to do with results once you have recorded them.
How can I tell which is which?
Ask one question: could a camera or a meter capture this? If yes, it is an observation. If you need scientific knowledge to say it, it is an explanation.
| Sentence | Type | Reason |
|---|---|---|
| The solution changed from blue to pale green | Observation | A colour can be seen |
| Iron is more reactive than copper | Explanation | It needs a reactivity idea |
| A reddish-brown solid formed on the nail | Observation | Appearance only |
| Copper was displaced from the solution | Explanation | Names a process |
Worked example: an iron nail in copper(II) sulfate
An original experiment: a clean iron nail is placed in blue copper(II) sulfate solution for 20 minutes. The question asks you to state two observations and explain them.
Observations. These use only what you can see.
- A reddish-brown solid forms on the surface of the nail.
- The blue solution slowly becomes pale green.
Explanation. Iron is more reactive than copper, so iron displaces copper from the solution. The brown solid is copper metal. The pale green colour comes from iron(II) ions entering the solution as the blue copper(II) ions are used up.
Each observation states a visible change, and a separate sentence gives the reason. Keeping the two apart makes it easy for a marker to give credit.
The mistake that costs marks
A common answer to “state what you observe” is: “Iron displaces copper because it is more reactive.” The science is correct, but it answers a different question.
| Question asks | Weak answer | Stronger answer |
|---|---|---|
| State the observation | Iron displaces copper | A reddish-brown solid forms on the nail |
| Explain the observation | The nail turned brown | Iron is more reactive, so it displaces copper, which deposits as a brown solid |
The fix is to read the command word first. “State”, “describe what you see” and “record” ask for observations. “Explain”, “why” and “suggest a reason” ask for theory.
A quick two-column habit
Before writing, draw two short columns on your rough paper: Seen and Because. Put each fact in the column where it belongs, then write the answer in the order the question asks.
This takes a few seconds. It also helps when a question wants both parts in one answer, because the pairs are already matched.
Check yourself
A ticker tape is pulled through a timer behind a trolley rolling down a ramp. The dots on the tape are close together at the start and further apart near the end. Write one observation and one explanation.
Answer
Observation: the gaps between dots become larger along the tape.
Explanation: the trolley covers a greater distance in each equal time interval, so its speed is increasing. A steady increase in speed means the trolley is accelerating down the ramp.
A weak answer would write “the trolley accelerates” as the observation. Acceleration is worked out from the gaps, so it belongs with the explanation.
What to study next
Go on to interpreting a small evidence table, then test yourself with the original mixed practice. The structured answer self-review tool helps you check your own answers against the question’s command word.
If you want a teacher to go through your own written answers, see online one-to-one Additional Science tuition.