AS AQA Chemistry Unit 1: January 2020 Examiner Report Analysis | AS AQA 化学单元1：2020年1月考官报告分析

📚 AS AQA Chemistry Unit 1: January 2020 Examiner Report Analysis | AS AQA 化学单元1：2020年1月考官报告分析

This article is based on the common errors highlighted in the January 2020 AQA AS Chemistry Unit 1 examiner’s report. We have organised the feedback into ten revision-ready sections so you can target the areas where marks were most frequently lost.

本文基于 AQA AS 化学单元1 在2020年1月考官报告中强调的常见错误编写。我们将反馈整理为十个复习模块，帮助你精准定位最容易失分的考点。

---

1. Atomic Structure and Ionisation Energy | 原子结构与电离能

Candidates often confused the charge and mass of subatomic particles. Protons have a relative charge of +1 and a relative mass of 1; neutrons have a relative charge of 0 and a relative mass of 1; electrons have a relative charge of −1 and a negligible mass.

考生常混淆亚原子粒子的电荷与质量。质子的相对电荷为 +1，相对质量为1；中子的相对电荷为0，相对质量为1；电子的相对电荷为 −1，质量可忽略不计。

Many students wrote isotope notation incorrectly. For example, carbon-14 should be written as ¹⁴₆C, where the top-left number is the mass number (protons + neutrons) and the bottom-left number is the atomic number (protons).

许多学生写错同位素符号。例如，碳-14 应写成 ¹⁴₆C，左上角数字是质量数（质子+中子），左下角数字是原子序数（质子数）。

For first ionisation energy, the definition is: the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions. The examiner noted that answers missing the state symbols ‘gaseous’ did not gain full marks.

第一电离能的定义是：从一摩尔气态原子上移走一摩尔电子，形成一摩尔气态 +1 离子所需的能量。考官指出，若答案缺少“气态”这一状态标识，则不能得满分。

Across Period 3, first ionisation energy generally increases due to increasing nuclear charge and decreasing atomic radius. However, there is a drop between magnesium and aluminium because aluminium’s outer electron is in a 3p orbital, higher in energy and better shielded than the 3s pair.

在第三周期中，第一电离能总体随核电荷增加和原子半径减小而增大。然而，镁到铝之间出现下降，因为铝的外层电子进入 3p 轨道，其能量更高且屏蔽效应比 3s 电子对更强。

---

2. Amount of Substance and Moles | 物质的量与摩尔计算

The fundamental relationship n = m / M remains a major source of error. Candidates often used molar mass with the wrong units. Molar mass must be in g mol⁻¹, and mass must be in grams.

基本关系式 n = m / M 仍是主要失分点。考生常将摩尔质量单位用错。摩尔质量必须以 g mol⁻¹ 表示，质量必须以克为单位。

n = m / M

In titration calculations, examiners reported candidates failing to convert cm³ into dm³. Remember to divide the volume in cm³ by 1000 to obtain dm³ before using c = n / V.

在滴定计算中，考官报告考生未将 cm³ 换算为 dm³。请记住：使用 c = n / V 前，需将体积以 cm³ 表示的数值除以1000，得到 dm³。

For empirical formula determination using combustion data, candidates often did not divide the mass of each element by its relative atomic mass before finding the simplest ratio. Always start with: moles of element = mass of element / molar mass of element.

在利用燃烧数据确定实验式时，考生常未先将各元素质量除以其相对原子质量，再找最简整数比。应始终先计算：元素的物质的量 = 元素质量 / 元素摩尔质量。

The ideal gas equation pV = nRT also caused difficulty. Pressure must be in Pa, volume in m³, and temperature in K. If using kPa and cm³, conversion is essential.

理想气体方程 pV = nRT 也是难点。压强必须以 Pa 为单位，体积以 m³ 为单位，温度以 K 为单位。若题目给出 kPa 和 cm³，则必须先进行换算。

---

3. Bonding and Intermolecular Forces | 化学键与分子间作用力

Many students could not distinguish between ionic, covalent and metallic bonding. Ionic bonding is the electrostatic attraction between oppositely charged ions; covalent bonding is the sharing of a pair of electrons; metallic bonding is the attraction between delocalised electrons and positive metal ions.

许多学生无法区分离子键、共价键和金属键。离子键是带相反电荷离子间的静电吸引力；共价键是共用一对电子；金属键是自由电子与金属正离子间的吸引力。

When predicting shapes, candidates often ignored lone pairs. A molecule with four electron pairs, two bonding and two lone pairs, is bent (non-linear) with an angle of about 104.5°, not tetrahedral.

在预测分子构型时，考生常忽略孤对电子。一个含四对电子、其中两对成键、两对孤对的分子为“V形”（非直线形），键角约 104.5°，而不是正四面体。

The examiner’s report highlighted confusion between electronegativity and polarity. A molecule can have polar bonds yet be non-polar overall if the dipoles cancel, as in CO₂.

考官报告特别指出，学生常混淆电负性与极性。一个分子可以有极性键，但如果偶极相互抵消，则分子整体为非极性，例如 CO₂。

Hydrogen bonding is the strongest intermolecular force, but it is only present when hydrogen is attached to nitrogen, oxygen, or fluorine. Candidates often stated that any molecule containing hydrogen can show hydrogen bonding, which is incorrect.

氢键是最强的分子间作用力，但仅当氢与氮、氧或氟相连时才存在。考生常认为含氢的任何分子都能形成氢键，这是错误的。

---

4. Periodicity and Periodic Trends | 元素周期律与周期性趋势

Across a period, atomic radius decreases because electrons are added to the same principal shell while nuclear charge increases, pulling electrons closer. Examiners noted that many students wrote ‘more protons’ without linking to increased attraction.

同周期从左到右，原子半径减小，因为电子进入同一主电子层，而核电荷增加，对电子的吸引力更强。考官指出，许多学生只写“质子更多”，却没有联系到吸引增强。

Electronegativity increases across a period and decreases down a group. Down a group, the atomic radius increases and shielding increases, reducing the attraction between the nucleus and bonding electrons.

电负性同周期从左到右增大，同主族从上到下减小。同主族向下，原子半径增大且屏蔽效应增强，导致原子核对成键电子的吸引力减弱。

For Group 2 elements, reactivity increases down the group because the sum of the first two ionisation energies decreases enough to overcome the increasing lattice or hydration enthalpy. Students should explain this in terms of atomic radius and shielding, not just ‘more shells’.

对第2族元素，同主族向下反应性增大，因为前两级电离能之和降低足以补偿晶格焓或水合焓变化。解释时应从原子半径与屏蔽效应入手，而不仅是“电子层更多”。

For Group 7 elements, electronegativity and oxidising ability decrease down the group. Chlorine can displace bromine from bromide ions, but iodine cannot displace chlorine. Many students forgot the half equations for these displacement reactions.

对第7族元素，电负性和氧化性随原子序数增大而减弱。氯可将溴从溴化物中置换出来，但碘不能置换氯。许多学生忘记写出这些置换反应的半方程式。

---

5. Energetics and Hess’s Law | 能量学与盖斯定律

Exothermic reactions have a negative ΔH; endothermic reactions have a positive ΔH. Candidates often wrote the sign correctly but failed to state the units kJ mol⁻¹, which were required for the mark.

放热反应的 ΔH 为负值，吸热反应的 ΔH 为正值。考生常能写对符号，但漏掉单位 kJ mol⁻¹，导致不能得分。

In calorimetry, the equation q = mcΔT is used to find heat energy. Examiners reported that students used the mass of the substance being burned rather than the mass of the solution, or used the temperature rise in °C instead of K (which is numerically the same but must be stated correctly).

量热法中，使用 q = mcΔT 计算热能。考官报告称，学生常误用被燃烧物质的质量而忽略了溶液质量，或将温度变化以 °C 代替 K（数值相同，但表述必须正确）。

Hess’s law states that the enthalpy change for a reaction is independent of the route taken. When constructing a Hess cycle, candidates often forgot to reverse the enthalpy sign when reversing a step, or failed to multiply the enthalpy values by the stoichiometric coefficients.

盖斯定律指出，反应焓变与反应路径无关。在构建盖斯循环时，考生常在逆向步骤中忘记改变焓符号，或忘记将焓值乘以反应的化学计量系数。

For bond enthalpy calculations, ΔH = Σ(bonds broken) − Σ(bonds formed). The mean bond enthalpy is always positive for bond breaking. A common error is to apply the formula in the opposite direction, giving a misleading sign for the reaction enthalpy.

键焓计算中，ΔH = Σ(断裂键能) − Σ(形成键能)。平均键焓对断键而言始终为正值。常见错误是公式用反，导致反应焓变符号错误。

---

6. Kinetics and Collision Theory | 化学动力学与碰撞理论

For a reaction to occur, particles must collide with enough energy greater than or equal to the activation energy and with the correct orientation. Many candidates stated only ‘they collide more often’ without mentioning energy or orientation.

反应发生要求粒子发生碰撞，且碰撞能量必须大于或等于活化能，并具备正确取向。许多学生只写“碰撞更频繁”，却未提及能量或取向。

On a Maxwell-Boltzmann distribution, increasing temperature makes the peak lower and shifts it to the right. The area under the curve remains the same because the total number of particles is unchanged. The shaded area representing particles with energy above Ea increases.

在麦克斯韦-玻尔兹曼分布曲线上，升高温度会使峰值降低并右移。曲线下面积保持不变，因为粒子总数目不变。代表能量高于 Ea 的粒子的阴影区域面积增大。

Catalysts increase the rate by providing an alternative pathway with lower activation energy. Examiners said that candidates often mixed up the idea of ‘lowering activation energy’ with ‘raising the energy of particles’.

催化剂通过提供一条活化能更低的替代路径来增大速率。考官指出，学生常将“降低活化能”与“提高粒子能量”混为一谈。

When pressure is increased in a gas phase reaction, the rate increases because gas particles are in a smaller volume, so collision frequency increases. Do not say ‘the particles move faster’; temperature is the factor that changes particle speed.

对气相反应增大压强，速率增大是因为气体粒子占据的体积减小，碰撞频率增加。不要说“粒子运动更快”；改变粒子运动速度的因素是温度。

---

7. Equilibria and Le Chatelier’s Principle | 化学平衡与勒夏特列原理

Dynamic equilibrium occurs when the forward and reverse reactions take place at the same rate, and the concentrations of reactants and products remain constant. Candidates often defined equilibrium as ‘equal amounts’ rather than ‘equal rates’.

动态平衡是指正逆反应速率相同，反应物和生成物浓度保持不变。考生常将平衡误定义为“物质的量相等”，而非“速率相等”。

For a general reaction aA + bB ⇌ cC + dD, the equilibrium constant expression is:

对一般反应 aA + bB ⇌ cC + dD，平衡常数表达式为：

Kc = [C]ᶜ[D]ᵈ / ([A]ᵃ[B]ᵇ)

Examiners reported that students frequently omitted the powers from Kc expressions or included solids and pure liquids

Published by TutorHao | AS Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）