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Command words tell you exactly what the examiner expects. Misreading a command word is one of the most common reasons students lose marks — not because they lack knowledge, but because they answer a different question from the one being asked. This lesson covers every command word you will encounter in Edexcel Chemistry, with multiple worked examples and common pitfalls for each.
These require a brief, factual answer — often a single word, phrase, or short sentence. No explanation is needed. Resist the urge to write more; additional detail wastes time and sometimes introduces errors that contradict your correct answer.
Example 1: "State the trend in first ionisation energy across Period 3." Good answer: "First ionisation energy generally increases across Period 3."
Example 2: "Name the type of bonding in magnesium chloride." Good answer: "Ionic bonding."
Example 3: "Give the formula of the precipitate formed when silver nitrate is added to sodium chloride solution." Good answer: "AgCl"
Common mistake: Writing a paragraph when a single sentence would score full marks. If a question is worth 1 mark and says "state," your answer should be one sentence at most.
Describe means say what happens — report observations, trends, or features. You do not need to explain why. Think of yourself as a camera recording events.
Example 1: "Describe what you would observe when chlorine water is added to potassium bromide solution." Good answer: "The solution changes from colourless to orange/brown as bromine is displaced."
Example 2: "Describe the trend in atomic radius down Group 7." Good answer: "Atomic radius increases down Group 7 from fluorine to iodine."
Example 3: "Describe the changes observed when concentrated sulfuric acid is added to solid sodium bromide." Good answer: "White/misty fumes of HBr are produced. The solution may turn orange/brown as some HBr is oxidised to Br₂. Choking fumes and a smell of bad eggs (H₂S) indicate further reduction of H₂SO₄."
Key principle: For "describe" questions involving observations, always include colours, state changes, gas production, and temperature changes. Be specific — "a colour change" is weaker than "the solution changes from colourless to orange."
Explain means say what happens AND why. This is the most commonly misunderstood command word. Many students describe when asked to explain, losing half the available marks.
Example 1: "Explain why the first ionisation energy of oxygen is lower than that of nitrogen." Good answer: "Oxygen has a paired electron in the 2p subshell, which experiences additional electron-electron repulsion, making it easier to remove compared to nitrogen's unpaired 2p electrons."
Example 2: "Explain why the rate of reaction increases when temperature increases." Good answer: "At higher temperature, molecules have greater kinetic energy, so a greater proportion of collisions exceed the activation energy. This increases the frequency of successful collisions, so the rate increases."
Example 3: "Explain why diamond has a very high melting point." Good answer: "Diamond has a giant covalent structure with each carbon atom bonded to four others by strong covalent bonds in a tetrahedral arrangement. A large amount of energy is required to break these many strong bonds, so the melting point is very high."
The critical difference: A describe answer says "ionisation energy decreases." An explain answer says "ionisation energy decreases because increasing shielding outweighs increasing nuclear charge, making the outer electron easier to remove."
Compare requires you to discuss both items, identifying similarities and/or differences. A one-sided answer scores poorly. Use comparative language throughout.
Example: "Compare the bonding in sodium chloride and ice." Good answer: "Sodium chloride has ionic bonding — strong electrostatic attractions between Na⁺ and Cl⁻ ions in a lattice. Ice has covalent bonds within H₂O molecules and hydrogen bonds between molecules. Both have high melting points relative to simple molecular substances, but sodium chloride melts at a much higher temperature (801°C vs 0°C) because ionic bonds are stronger than hydrogen bonds."
Key words to use: "whereas," "in contrast," "however," "both," "similarly," "unlike," "while."
Common mistake: Discussing each item separately without explicit comparison. Writing two paragraphs (one about NaCl, one about ice) without linking them scores lower than a paragraph that directly compares them point by point.
Suggest indicates the answer requires you to apply your knowledge to an unfamiliar context. There may be more than one acceptable answer. The mark scheme often has a broad range of acceptable responses.
Example: "A new catalyst is found to increase the yield of ammonia at lower temperatures. Suggest why this is economically beneficial." Good answer: "Lower temperatures require less energy input for heating, reducing fuel costs. A higher yield means less unreacted starting material needs to be recycled, improving efficiency. Both factors reduce the overall production cost per tonne of ammonia."
Key principle: "Suggest" tells you the answer is not directly in the specification. Do not try to recall a memorised answer — instead, apply chemical principles to reason through the new situation.
Show your working clearly. Include units. Give your answer to an appropriate number of significant figures.
Example: "Calculate the concentration of hydrochloric acid given that 23.50 cm³ of 0.100 mol dm⁻³ NaOH neutralises 25.00 cm³ of the acid."
Moles of NaOH = 0.100 × (23.50/1000) = 2.350 × 10⁻³ mol Mole ratio NaOH : HCl = 1 : 1 Moles of HCl = 2.350 × 10⁻³ mol Concentration of HCl = 2.350 × 10⁻³ / (25.00/1000) = 0.0940 mol dm⁻³
Exam tip: Even if you can do the calculation in your head, write out each step. If your final answer is wrong by a factor of 10 due to a unit error, you can still earn method marks for every correct step shown.
Similar to calculate, but may involve interpreting data or graphs before performing a calculation.
Example: "Using the graph, determine the rate of reaction at t = 30 s." This requires you to first draw a tangent to the curve at t = 30 s, then calculate the gradient of that tangent. The "determine" signals that data extraction comes before calculation.
Draw a conclusion from the information provided. You are expected to reason logically from given data, not recall memorised facts.
Example: "The table shows that compound X has a molecular ion peak at m/z = 46 and a strong IR absorption at 3200-3600 cm⁻¹. Deduce the identity of compound X." Good answer: "M_r = 46 and the broad IR absorption suggests an O-H group. C₂H₆O (ethanol) has M_r = 46 and contains an O-H group, so compound X is ethanol."
Weigh up evidence or arguments and reach a supported conclusion. This typically appears in 6-mark questions and requires a balanced answer.
Example: "Evaluate the use of hydrogen as a fuel for cars." A good answer discusses advantages (zero carbon emissions at point of use, water as only product), disadvantages (energy-intensive production, storage challenges, explosive risk), and reaches a supported conclusion.
Common mistake: Being one-sided. If you only list advantages, you have not evaluated — you have advocated. Level 3 requires balanced consideration.
Give reasons for a decision or conclusion. Your answer must include supporting evidence.
Example: "A student uses phenolphthalein as the indicator for a strong acid-weak base titration. Justify whether this choice is appropriate." Good answer: "This is not appropriate. A strong acid-weak base titration has an equivalence point below pH 7 (typically around pH 4-5). Phenolphthalein changes colour between pH 8.2 and 10.0, which does not overlap with the equivalence point. Methyl orange (pH 3.1-4.4) would be more suitable."
| Command word | What to do | Marks typically | Common mistake |
|---|---|---|---|
| State/Give/Name | Brief factual answer | 1 | Writing too much |
| Describe | Say what happens | 2-3 | Explaining why (wasting time) |
| Explain | Say what happens AND why | 2-4 | Only describing |
| Compare | Discuss both items with explicit links | 3-4 | Only discussing one item |
| Suggest | Apply knowledge to new context | 2-3 | Giving a memorised answer |
| Calculate | Show working, units, sig figs | 2-5 | No working shown |
| Determine | Interpret data, then calculate | 2-4 | Skipping data extraction step |
| Deduce | Reason from given information | 2-3 | Guessing without using the data |
| Evaluate | Both sides, then conclude | 6 | Being one-sided |
| Justify | Give reasons with evidence | 2-4 | Stating a conclusion without reasoning |
If a question asks you to explain, check that your answer contains the word "because" (or an equivalent such as "due to," "as a result of," "this is caused by"). If it does not, you are probably describing rather than explaining.
graph TD
A[Read the question] --> B{Does it say 'explain'?}
B -->|Yes| C[Write your answer]
C --> D{Does your answer contain 'because' or equivalent?}
D -->|Yes| E[Good - you are explaining]
D -->|No| F[You are probably only describing]
F --> G[Add the reason using 'because...']
G --> E
B -->|No| H{What command word is it?}
H --> I[Match your response to the command word]
Consider the topic of electronegativity across Period 3:
"State the trend in electronegativity across Period 3." (1 mark)
Electronegativity increases across Period 3.
"Describe the trend in electronegativity across Period 3." (2 marks)
Electronegativity increases across Period 3 from sodium (0.93) to chlorine (3.16). The increase is not uniform — there is a larger increase between the metals and non-metals.
"Explain the trend in electronegativity across Period 3." (3 marks)
Electronegativity increases across Period 3 because the nuclear charge increases while the shielding remains approximately constant (electrons are added to the same shell). This means the bonding pair of electrons is more strongly attracted to the nucleus, so atoms have a greater ability to attract electrons in a bond.
Notice how the same underlying knowledge is presented differently depending on the command word, and each version earns its marks for a different reason.
Command words are the contract between examiner and candidate. Each one binds the answer to a specific Assessment Objective (AO1 recall, AO2 application, AO3 analysis/evaluation), and each one carries a different mark-scheme expectation. A candidate who reads "explain" but answers as if it said "describe" can give chemically correct material and still score zero on a 4-marker. This deeper strategy section turns command-word fluency into a scoring system you can deploy in real time.
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