IB Chemistry command terms: the complete student guide
11 min readOliver Kidd (Co-founder)17 Jun 2026
IB Chemistry command terms are precise instructional verbs that tell you exactly what type of response an examiner expects. Familiarity with command terms allows you to produce targeted, effective answers rather than vague ones that lose marks. Terms like explain, describe, calculate, and suggest each carry a specific meaning. Miss that meaning and you miss the marks, regardless of how well you know the chemistry. Understanding these terms is one of the most direct ways to improve your IB Chemistry exam performance.
1. What are IB Chemistry command terms?
IB Chemistry command terms are the official instructional verbs used across all IB Chemistry assessments. The IB Chemistry syllabus uses these terms to guide both teaching and marking, making them central to every exam question. They tell you whether to recall a fact, build an argument, or carry out a calculation. Treating them as interchangeable is the single most common reason students underperform in papers they feel confident about.
2. The top 10 command terms every student must know
These are the ten assessment terms you will encounter most frequently in IB Chemistry exams. Learn their exact meanings and you will know what every question is asking before you read the chemistry itself.
- State — Give a specific fact, value, or name with no explanation required. One sentence is usually enough.
- Identify — Select and name a feature, substance, or property from given information.
- Describe — Observable features only, reported factually. Do not explain causes or reasons.
- Outline — Provide a brief account covering the key points without full detail.
- Explain — Show cause and effect. Use linking words such as because or therefore to connect your reasoning. Explain demands cause-effect reasoning, not just description.
- Calculate — Show your working in full: formula, substitution, units, and significant figures. Full marks require method, substitution, and units, so never write only a final answer.
- Deduce — Reach a conclusion from given data using logical reasoning. The data does the heavy lifting; your job is to interpret it correctly.
- Suggest — Propose a plausible option with brief justification. There is often more than one acceptable answer.
- Justify — Give reasons or evidence to support a claim or decision. This goes further than suggest by requiring a stronger line of reasoning.
- Evaluate — Weigh up evidence, consider strengths and limitations, and reach a supported conclusion.
Pro Tip: Read the command term before you read the rest of the question. This primes your brain to filter the chemistry through the correct type of response from the start.
3. How do similar command terms differ in their expectations?
Confusing similar terms is where most marks are lost. The differences are subtle but the marking consequences are significant.
| Command term pair | Key distinction |
|---|---|
| Explain vs Describe | Explain requires cause and effect; Describe reports observable facts only |
| Suggest vs Justify | Suggest needs a plausible idea with brief reasoning; Justify demands stronger supporting evidence |
| Deduce vs Calculate | Deduce draws a conclusion from given data; Calculate requires a numerical method with working shown |
| Outline vs Explain | Outline gives a brief overview; Explain requires full causal reasoning |
Describe asks you to report what you observe, such as the colour change in a titration. Explain asks you why that change occurs, linking it to the underlying chemistry. Misinterpreting these terms leads directly to lower marks, even when the underlying knowledge is sound.
Pro Tip: When you see Deduce, look at the data provided in the question first. The answer is always derivable from what is given. If you find yourself relying on memorised facts alone, you are probably answering the wrong question.
4. How to apply command terms to improve your exam performance
Knowing the definitions is only half the work. Applying them under exam conditions is where the real skill lies. These four steps will help you use chemical command terms accurately every time.
- Underline the command term first. Underlining before answering creates a mental focus that shapes your entire response. It takes two seconds and prevents you from drifting into the wrong type of answer.
- Match your answer length to the term. State warrants one sentence. Evaluate warrants a structured paragraph with a conclusion. The number of marks available is a further guide to length.
- Use causal language for Explain questions. Words like because, therefore, which causes, and as a result signal to the examiner that you are building a cause-and-effect argument, not just describing.
- Practise with past papers and mark schemes. The IB exam-style questions in past papers show exactly how command terms appear in context. Reading mark schemes trains you to see what a full-mark answer looks like for each term.
- Use official IB terminology. Exact IB phrases such as conjugate base or activation energy are the safest choices. Markers accept clear synonyms, but precise language removes all ambiguity.
5. What role do command terms play in marking and grading?
Examiners use command terms to set the boundary for what a full-mark answer looks like. The term defines the depth, not just the topic.
- A response to State that includes unnecessary explanation wastes time and gains no extra credit.
- A response to Explain that only describes will score partial marks at best, regardless of accuracy.
- Markers reward clarity and precise use of terminology aligned with the command term. Vague or generic answers do not score well even when the chemistry is broadly correct.
- IB examiners expect precise, reasoned responses that match the command term, not answers that demonstrate general knowledge without structure.
The practical implication is clear. Aligning your answer structure to the command term is not just good exam technique. It is the mechanism by which marks are awarded. You can read more about this in the IB Chemistry exam guide on the Tibertutor blog.
Key takeaways
IB Chemistry command terms define the exact type and depth of response required, and matching your answer to the term is the most direct route to higher marks.
| Point | Details |
|---|---|
| Command terms set answer depth | Each term defines whether to recall, reason, calculate, or evaluate. |
| Explain and Describe are not the same | Explain requires cause-and-effect language; Describe reports facts only. |
| Calculate demands full working | Show formula, substitution, units, and significant figures for full marks. |
| Underline before you answer | This simple habit keeps your response focused on the correct type of answer. |
| Precise terminology matters | Use official IB phrases to avoid ambiguity and protect your marks. |
Why command terms changed how I think about exam preparation
Students often tell me they revised hard but still felt the exam did not reflect their knowledge. In most cases, the issue is not the chemistry. It is the command terms. I have seen students write beautifully accurate descriptions in response to Explain questions and score half marks. The knowledge was there. The structure was not.
What I find genuinely useful is treating command terms as a separate revision topic. Not a footnote, but a dedicated session early in your preparation. Once you internalise the difference between deduce and calculate, or between suggest and justify, you start reading questions differently. You stop asking “what do I know about this?” and start asking “what is this question asking me to do?” That shift in thinking is worth more than an extra hour of content revision.
The same applies to educators. Embedding command term awareness into classroom questioning, as explored in classroom questioning strategies, helps students build this habit long before exam season. When students hear explain and describe used precisely in lessons, they carry that precision into their answers.
— Oliver
Build your command term confidence with Tibertutor
Tibertutor is built by IB examiners and experienced educators who understand exactly how command terms shape marking. The platform gives you access to an IB Science question bank packed with exam-style questions organised by command term, so you can practise explain, deduce, and evaluate questions in isolation until the responses feel natural. Detailed mark schemes, animated videos, and personalised progress tracking mean you always know where to focus next.
Whether you are aiming for a 7 or working to consolidate a 5, Tibertutor’s student resources give you the structure and confidence to walk into your IB Chemistry exam fully prepared. Start practising with command-focused questions today and see the difference precision makes.
FAQ
What are IB Chemistry command terms?
IB Chemistry command terms are official instructional verbs used in exam questions to indicate the required type and depth of response. Examples include state, explain, calculate, and evaluate.
How is Explain different from Describe in IB Chemistry?
Describe requires factual reporting of observable features without reasons. Explain requires cause-and-effect reasoning, using linking words such as because or therefore.
Do command terms apply to IB Biology as well?
Yes. IB Biology command terms follow the same IB framework and include many of the same verbs, such as outline, deduce, and evaluate, with equivalent expectations for depth and structure.
How should I answer a Calculate question for full marks?
Show the formula, substitute the values, include units, and give your answer to the correct number of significant figures. Writing only a final answer will not earn full marks.
Why do students lose marks on command term questions?
The most common reason is misreading the command term and providing the wrong type of response, such as describing when asked to explain, or stating when asked to justify.