Catalyst Revision
Guides › National 5 Chemistry
How to answer N5 Chemistry open-ended questions
A simple method, a marked example, and the mistakes that cost the most marks.
Open-ended questions are worth 3 marks each, and the pupils who score well follow the same simple routine: pick the relevant chemistry, explain it clearly, and link it back to the question.
You'll spot them in the National 5 Chemistry exam by the phrase “Using your knowledge of chemistry”, usually followed by “comment on”, “explain” or “suggest”. There's no single right answer, which is exactly why so many pupils freeze or write two lines and move on.
This guide covers how these questions are marked, a step-by-step method, a worked example with weak, reasonable and strong answers, and the mistakes that cost marks most often.
How open-ended questions are marked
Markers don't tick off a list of facts. They read the whole answer and judge how well it shows you understand the chemistry.
| Mark | What the marker is looking for |
|---|---|
| 3 | A good understanding: the right chemistry, explained clearly and applied to the situation in the question |
| 2 | A reasonable understanding: mostly correct chemistry, but some gaps or little explanation |
| 1 | A limited understanding: at least one relevant, correct statement |
| 0 | No relevant chemistry, or chemistry that is wrong |
Two things follow from this. First, a long answer isn't automatically a good one: three well-explained points beat ten vague ones. Second, you can't lose marks for trying. A sensible attempt almost always earns something, so never leave one blank.
A five-step method
- Read the statement twice and find the claim. Most questions quote someone. Work out exactly what they're claiming, and whether it's true, false or partly true.
- Spot the topics. Ask: which parts of the course does this touch? Bonding and structure? Rates? Fuels? Write the topic names in the margin.
- List what you know. Jot down three or four relevant facts, keywords or examples before you write a sentence. This takes a minute and stops you drying up halfway.
- Explain, don't just state. For each point, add a “because” or “so”. “Graphite conducts” is a fact; “graphite conducts because it has delocalised electrons that can move” is understanding.
- Come back to the question. Finish with a sentence that answers it directly: “So the statement is partly true, because…”. This is what turns a 2 into a 3.
Aim for about 6 to 8 lines, and spend no more than 5 or 6 minutes on each question.
Tip: come back to them at the end. If an open-ended question doesn't click straight away, jot down a few keywords and move on. Other questions in the paper often jog your memory about the chemistry you need. Return to it once you've worked through the rest of the exam, so it doesn't eat into time for questions you can answer quickly.
Worked example: three answers to the same question
The question: A pupil says: “Methane (CH4) and methanol (CH3OH) are both small molecules with one carbon atom, so they should behave in much the same way.” Using your knowledge of chemistry, comment on this statement. (3 marks)
1 mark Limited
Methane is a gas and methanol is a liquid, so they are different.
This is correct, but it only states a difference. There's no chemistry explaining why, and no judgement of the statement.
2 marks Reasonable
Methane is an alkane and methanol is an alcohol. Methanol has a hydroxyl group, so it has a higher boiling point and is a liquid. Methanol also dissolves in water but methane doesn't. Both burn, so both can be used as fuels.
Good, relevant chemistry, and several correct points. But the boiling point isn't really explained, and the answer never says whether the pupil's statement is right.
3 marks Good
The statement is only partly true. Both molecules are small and contain one carbon atom, and both burn to give carbon dioxide and water, so both are used as fuels. But methanol belongs to a different homologous series: it is an alcohol, with a hydroxyl (−OH) group. The −OH group makes the forces of attraction between methanol molecules much stronger than those between methane molecules, so more energy is needed to separate them. That's why methane is a gas at room temperature but methanol is a liquid. The −OH group also lets methanol mix with water, while methane doesn't dissolve. So the functional group matters more than the number of carbon atoms.
This answer explains each point with a “because” or “so”, covers similarities and differences, and ends by judging the statement. That's what a marker means by a good understanding.
Common mistakes that cost marks
- Listing facts without explaining them. Each point needs a reason. Without one, even five correct facts often only earn 1 or 2 marks.
- Not answering the question. If the question asks you to comment on a statement, say whether you agree and why. Don't copy out or reword the question itself: it earns no marks and uses up time.
- Writing everything you know about the topic. Stick to what's relevant. Extra chemistry that's wrong can pull your mark down.
- Mixing up key words. Classic examples: “covalent bonds break” when a molecular substance melts (it's the forces between molecules that are overcome), or “electrons move” in a molten ionic compound (it's the ions).
- Leaving it blank. A sensible attempt with one correct, relevant point usually earns at least 1 mark.
- Spending too long. Open-ended questions are worth 3 marks, the same as one calculation. Don't spend 15 minutes on one and run out of time.
How to practise (and how parents can help)
The fastest way to improve is to answer real exam-style questions, then compare your answer with a marked example.
- Time yourself. Give yourself 6 minutes per question, as in the exam.
- Mark against the guidance, then rewrite. Find what a strong answer included that yours didn't, and write a second version.
- Practise on different topics. Open-ended questions can come from any part of the course, so don't only practise on your favourite topic.
Parents: you don't need to know any chemistry to help. Ask your child to talk you through their answer, then ask “why?” after each point. If they can't answer, that's the explanation the marker is looking for. Then check their written answer against the marking guidance together.