IGCSE Chemistry 0620 command words explained

• State: give a short, exact fact. No reason needed. Example: "State the colour of copper(II) hydroxide." Answer: light blue.
• Give: produce an answer from memory or from the information given. Often just a name, formula or value. Example: "Give the formula of ethene." Answer: C₂H₄.
• Name: give the chemical name. A formula is not a name. Example: "Name the gas that relights a glowing splint." Answer: oxygen.
• Identify: name or pick out exactly. Example: "Identify the gas that turns limewater milky." Answer: carbon dioxide, not "a gas".

Describe asks what happens or what you see. Explain asks why or how, and usually needs "because".

Define means give the precise meaning. Learn definitions word for word, because one missing key word can cost the mark.

Example: "Define isotopes." Answer: atoms of the same element with the same number of protons but different numbers of neutrons.

• Compare: give similarities and/or differences. Mention both things in the same sentence. Example: "Diamond has no free electrons but graphite has delocalised electrons, so only graphite conducts."
• Contrast: differences only. Use comparing words such as higher, lower, faster. Example: "Potassium reacts faster with water than sodium does."

• Calculate: work it out from the figures given. Show working, give the unit, round at the end. Example: moles in 36 g of water = 36 ÷ 18 = 2.0 mol.
• Determine: use the information given to reach one definite answer. Example: find the volume of acid used from two burette readings.
• Deduce: reach a conclusion from the information given. Point to the clue. Example: "A cream precipitate forms with silver nitrate, so the solution contains bromide ions."
• Show that: the answer is printed. The marks are for the working that reaches it, so every step must be visible.

• Predict: say what is likely to happen, following a trend. Example: "Predict the state of astatine at room temperature." Answer: solid, following the Group VII trend.
• Suggest: there is more than one valid answer. Use chemistry you know to give a sensible one. Example: "Suggest why the reaction slowed down." Answer: the acid was being used up, so its concentration fell.
• Analyse: look at the data in detail and say how the pieces are linked.
• Consider: review the information printed in the question and respond to it, rather than just recalling facts.
• Examine: look closely at every part of the information before answering.

• Discuss: write in depth, in a structured way. Give points on both sides, then a short conclusion. Example: fermentation vs hydration of ethene to make ethanol.
• Evaluate: judge how good, reliable or important something is, and give a reason. Example: "The results are reliable because the three titres agree within 0.10 cm³."
• Justify: back up your answer with evidence: a number, an observation or a rule.
• Demonstrate: show how, or give an example or worked line that proves the point.

• Sketch: a simple drawing with the key features. For a graph, label the axes and get the shape right, such as a curve that rises then levels off as a reaction finishes.
• Write: usually a formula or equation. Symbol equations must balance.
• Complete: fill every gap in a table, diagram or equation, then check it still balances.

• Round a calculated answer to the same number of significant figures as the least precise data (usually 2 or 3), and only at the end.
• Always give units, such as g, mol, dm³, mol/dm³ or kJ/mol. Remember 1 dm³ = 1000 cm³.
• Read scales to the nearest half of the smallest division. A burette reads to 0.05 cm³.
• For a test, write what you see ("white precipitate"), not the conclusion.
• Add state symbols when the question asks for them.