📚 After the Exam: IGCSE Chemistry Post-Mock Error Analysis | 考后复盘：IGCSE 化学易错点与应试策略
After any IGCSE Chemistry mock or past paper, the most productive step is not simply checking the mark, but carrying out a structured error analysis. This article reviews the highest-frequency misconceptions and calculation traps that students meet in Paper 2, Paper 4 and Paper 6, so you can turn 'after the exam' into a targeted revision plan.
在任何一次 IGCSE 化学模拟考或真题练习之后，最有效的步骤不是只看分数，而是进行系统的错题分析。本文回顾学生在 Paper 2、Paper 4 和 Paper 6 中最常遇到的概念误区与计算陷阱，帮助你让"考后"成为有针对性的复习计划。
1. States of Matter and Diffusion | 物质状态与扩散
A classic post-exam error is describing diffusion as 'particles move from high concentration to low concentration' without linking it to kinetic theory. Examiners want you to state that particles move randomly and collide, and that lighter gas particles diffuse faster at a given temperature because they have higher average speed.
考后常见的错误是把扩散简单描述为"粒子从高浓度向低浓度运动"，却没有联系动力学理论。考官希望看到你说明粒子做无规则运动并相互碰撞，而且在相同温度下，较轻的气体粒子扩散更快，因为它们的平均速率更大。
Another frequent mark-loser is confusing boiling and evaporation. Boiling occurs at a fixed temperature throughout the liquid, while evaporation happens at the surface over a range of temperatures below the boiling point.
另一个常见失分点是混淆沸腾与蒸发。沸腾是在固定温度下、在液体内部和表面同时发生的剧烈汽化；蒸发则是在低于沸点的任意温度下、仅在液体表面进行的缓慢汽化。
When explaining a heating curve, do not say 'temperature stays constant because heat is lost'. The correct statement is that during a state change, energy is used to overcome intermolecular forces rather than to raise kinetic energy, so temperature remains constant.
解释加热曲线时，不要说"温度不变是因为热量散失"。正确的说法是：在状态变化过程中，能量用于克服分子间作用力，而不是增加粒子的动能，因此温度保持不变。
2. Atomic Structure and Isotopes | 原子结构与同位素
Students often write that isotopes have 'different numbers of protons'. This is wrong: isotopes of the same element have the same number of protons and electrons, but different numbers of neutrons, hence different mass numbers.
学生常误以为同位素"质子数不同"。这是错误的：同一元素的同位素具有相同的质子数和电子数，但中子数不同，因此质量数不同。
isotopic abundances, not by averaging mass numbers directly. Use the formula Ar = (mass₁ × %₁ + mass₂ × %₂) ÷ 100, and never forget to divide by 100 when percentages are given.
相对原子质量 (Ar) 是由同位素丰度计算得出的，而不是直接对质量数求平均。使用公式 Ar = (质量₁ × 丰度₁ + 质量₂ × 丰度₂) ÷ 100，并且当给出百分比时千万不要忘记除以 100。
Electronic configuration must be written as 2,8,8,2 for calcium (atomic number 20), not 2,8,10. The third shell can hold up to 18 electrons, but after 8 electrons fill the third shell, the fourth shell begins to fill before the third is completed.
钙（原子序数 20）的电子排布必须写作 2,8,8,2，而不是 2,8,10。第三壳层最多可容纳 18 个电子，但在第三层填满 8 个电子后，第四层会先开始填充，然后第三层才继续填满。
3. Ionic and Covalent Bonding | 离子键与共价键
A common post-paper error is stating that an ionic bond is 'the transfer of electrons'. The bond itself is the electrostatic attraction between oppositely charged ions formed after electron transfer. Saying 'transfer' alone misses the key force.
考后常见错误是把离子键说成"电子的转移"。离子键本身是电子转移后形成的带相反电荷离子之间的静电吸引力。只写"转移"没有答出关键的力。
When drawing dot-and-cross diagrams for covalent molecules, students often forget lone pairs or draw ionic structures for simple molecules such as H₂O and CO₂. Always show all outer-shell electrons, using different symbols for different atoms.
画共价分子的点叉图时，学生经常漏掉孤对电子，或者把 H₂O、CO₂ 等简单分子画成离子结构。一定要画出所有外层电子，并用不同符号表示不同原子。
Giant covalent structures such as diamond and graphite both have high melting points, but graphite conducts electricity because each carbon atom uses only three of its four outer electrons in covalent bonds, leaving delocalised electrons.
金刚石和石墨等巨型共价结构都有很高的熔点，但石墨能导电，因为每个碳原子只用了四个外层电子中的三个形成共价键，留下离域的电子。
4. Stoichiometry and Mole Calculations | 化学计量与摩尔计算
d before using molar ratios. Many students use the given mass directly in the ratio, which produces an incorrect limiting reagent or yield calculation.
在使用摩尔比之前，必须先应用摩尔公式 n = m ÷ M。许多学生直接把给定质量用于比例计算，导致限制试剂或产率的计算错误。
For gas volumes at room temperature and pressure (r.t.p.), one mole of gas occupies 24 dm³. To convert from cm³ to dm³, divide by 1000. A frequent slip is using 22.4 dm³, which only applies at standard temperature and pressure (s.t.p.).
在室温和常压 (r.t.p.) 下，一摩尔气体体积为 24 dm³。把 cm³ 转换为 dm³ 时要除以 1000。常见的失误是使用 22.4 dm³，这只适用于标准温度和压力 (s.t.p.)。
Empirical formula calculations require dividing the mass or percentage of each element by its relative atomic mass, then simplifying the mole ratio to the smallest whole numbers. Never round a ratio like 1:1.5 to 1:2; multiply by 2 to get whole numbers.
经验式的计算需要将各元素的质量或百分比除以各自的相对原子质量，然后把摩尔比化简为最小整数比。不要将 1:1.5 这样的比例直接四舍五入为 1:2；应乘以 2 得到整数比。
5. Electrolysis and Redox | 电解与氧化还原
In electrolysis of aqueous solutions, students often ignore the competition between ions. At the cathode, the less reactive metal or hydrogen is discharged; at the anode, a halide is preferred over hydroxide, but if no halide is present, oxygen is produced from OH⁻.
在电解水溶液时，学生经常忽略离子之间的竞争。在阴极，较不活泼的金属或氢离子优先放电；在阳极，卤离子优先于氢氧根离子放电，但如果没有卤离子，则从 OH⁻ 产生氧气。
ing oxidation only to gain of oxygen, which fails for reactions such as 2Na + Cl₂ → 2NaCl.
氧化还原必须从电子转移的角度描述：氧化是失去电子，还原是得到电子。常见错误是把氧化仅仅与"得氧"联系，对于 2Na + Cl₂ → 2NaCl 这类反应就无法适用。
In electroplating, the object to be plated is the cathode, and the anode is made of the plating metal. Students often reverse the electrodes, which would dissolve the object instead of coating it.
在电镀中，待镀物件是阴极，阳极由镀层金属制成。学生常把电极接反
Published by TutorHao | IGCSE Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图