📚 Mastering IGCSE Chemistry Command Words | 掌握IGCSE化学指令词
In IGCSE Chemistry, command words are the instructions in exam questions that tell you exactly what to do. Understanding them is just as important as knowing the science itself. Each command word signals the depth and type of answer expected, so misreading one can cost marks even when your chemical knowledge is correct.
在IGCSE化学中，指令词是考试题目中告诉你具体该做什么的指示语。理解它们与掌握科学知识本身同样重要。每个指令词都标志着所期望答案的深度和类型，因此即使你的化学知识正确，误读指令词也可能导致失分。
1. What Are Command Words? | 什么是指令词？
Command words are the verbs used by examiners to define the task. In IGCSE Chemistry, these words are carefully chosen and are directly linked to the mark scheme. For example, a question that begins with “state” is looking for a single fact, while a question that begins with “explain” is looking for reasons and links.
指令词是考官用来界定答题任务的动词。在IGCSE化学中，这些词经过精心选择，并直接与评分标准挂钩。例如，以“state”开头的问题要求一个单一事实，而以“explain”开头的问题则要求给出原因和联系。
| Command Word (指令词) | What you must do (你需要做什么) | Example (示例) |
| State (写出/说出) | Give a word, value or short phrase without explanation. 给出单词、数值或短语，无需解释。 | State the colour of bromine. 写出溴的颜色。 |
| Name (命名) | Give the correct chemical name. 给出正确的化学名称。 | Name the salt formed in this reaction. 命名该反应生成的盐。 |
| Describe (描述) | Say what happens or what is observed. 说出发生了什么或观察到什么。 | Describe the reaction of sodium with water. 描述钠与水的反应。 |
| Explain (解释) | Give reasons or causes for a phenomenon. 给出现象的理由或原因。 | Explain why diamond is hard. 解释为什么金刚石坚硬。 |
| Suggest (提出建议) | Apply knowledge to a new situation. 将知识应用到新情境中。 | Suggest a method to separate sand and salt. 提出分离沙子和食盐的方法。 |
| Calculate (计算) | Use numbers to work out an answer. 用数字得出答案。 | Calculate the number of moles in 4 g of NaOH. 计算4 g氢氧化钠的物质的量。 |
| Define (定义) | Give the precise scientific meaning. 给出精确的科学含义。 | Define the term ‘isotope’. 定义“同位素”这个术语。 |
| Compare (比较) | State similarities and differences. 说出相同点和不同点。 | Compare metals and non-metals. 比较金属与非金属。 |
| Predict (预测) | Use understanding to state what will happen. 运用理解说出将发生什么。 | Predict the pH of sodium chloride solution. 预测氯化钠溶液的pH。 |
| Deduce (推断) | Work out logically from evidence. 根据证据逻辑推理。 | Deduce the formula of magnesium oxide. 推断氧化镁的化学式。 |
| Outline (概述) | Give a short summary of main points. 给出要点的简短总结。 | Outline the steps of the Contact process. 概述接触法的主要步骤。 |
| Identify (识别) | Name something from given data or results. 根据给定数据或结果命名。 | Identify the gas that turns limewater milky. 识别使石灰水变浑浊的气体。 |
2. State / Name / Give | 写出 / 命名 / 给出
“State”, “Name” and “Give” are the most common low-demand command words. They usually carry one mark. You should write only the essential answer, with no explanation or working. For example, “State the colour of anhydrous copper(II) sulfate” requires just the word “white”.
“State”“Name”和“Give”是最常见的低要求指令词，通常为1分。你只需写出必要的答案，不需要解释或计算过程。例如，“写出无水硫酸铜的颜色”只需回答“白色”。
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State the colour of anhydrous copper(II) sulfate. → White.
写出无水硫酸铜的颜色。→ 白色。
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Name the salt produced when hydrochloric acid neutralises sodium hydroxide. → Sodium chloride.
写出盐酸与氢氧化钠中和生成的盐。→ 氯化钠。
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Give the formula of the nitrate ion. → NO₃⁻.
写出硝酸根离子的化学式。→ NO₃⁻。
3. Describe | 描述
“Describe” asks you to say what happens, what you see, or how something is carried out. It does not ask for reasons. In practical questions, your observation must be specific: colour change, gas evolved, precipitate formed, or temperature change.
“Describe”要求你说出发生了什么、看到了什么或某件事如何完成，不需要给出原因。在实验题中，你的观察结果必须具体：颜色变化、产生气体、形成沉淀或温度变化。
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Describe the reaction of sodium with water: sodium fizzes, moves on the water surface, and melts into a silver ball.
描述钠与水的反应：钠发出嘶嘶声，在水面上移动，并熔化成银色小球。
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Describe how to test for carbon dioxide: bubble the gas through limewater; a white precipitate forms.
描述如何检验二氧化碳：将气体通入石灰水，产生白色沉淀。
4. Explain | 解释
“Explain” is a high-demand command word. It requires you to give reasons, mechanisms and cause-and-effect links. Your answer should use connectives such as “because”, “so” and “therefore”. In IGCSE Chemistry, explanations often involve particles, bonding, energy changes or equilibrium.
“Explain”是高要求指令词，需要给出原因、机理和因果关系。答案中应使用“因为”“所以”“因此”等连接词。在IGCSE化学中，解释常涉及微粒、化学键、能量变化或平衡。
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Explain why ionic compounds have high melting points: strong electrostatic forces of attraction between oppositely charged ions require a large amount of energy to overcome.
解释为什么离子化合物熔点高：带相反电荷的离子之间存在强烈的静电引力，需要大量能量才能克服。
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Explain why a catalyst speeds up a reaction: it provides an alternative pathway with lower activation energy, so more particles have energy greater than the activation energy.
解释催化剂为什么加快反应速率：它提供了活化能较低的替代路径，因此更多微粒的能量超过活化能。
5. Suggest | 提出建议
“Suggest” is used when the question is not directly from the syllabus. You must apply your knowledge to an unfamiliar context. There may be several valid answers, so any scientifically reasonable explanation gains credit. Avoid writing one “perfect” fact; instead, give a logical suggestion using chemical principles.
“Suggest”用于不在考纲直接范围内的问题。你需要将知识应用到不熟悉的情境中，可能有多个正确答案，因此任何科学上合理的解释都能得分。不要只写一个“完美”的事实，而要运用化学原理给出合乎逻辑的建议。
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Suggest why ammonia is converted to nitric acid in industry. Possible answer: to manufacture nitrogenous fertilisers.
建议为什么工业上将氨转化为硝酸。可能答案：用于制造氮肥。
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Suggest one property of graphene that makes it useful in electronics. Possible answer: high electrical conductivity.
建议石墨烯在电子产品中有用的一个性质。可能答案：高导电性。
6. Calculate | 计算
“Calculate” requires numerical work. Always show your working because method marks are awarded even if the final answer is wrong. Include units in your final answer and pay attention to significant figures.
“Calculate”需要数值计算。务必展示计算过程，因为即使最终答案错误，方法分也会给分。最终答案要带单位，并注意有效数字。
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Calculate the number of moles in 4 g of sodium hydroxide (Mᵣ = 40). Use moles = mass / Mᵣ = 4 / 40 = 0.1 mol.
计算4 g氢氧化钠的物质的量（Mᵣ = 40）。使用 物质的量 = 质量 / 相对分子质量 = 4 / 40 = 0.1 mol。
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Calculate the concentration
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