📚 IGCSE OCR Chemistry: Final Revision Notes | IGCSE OCR 化学：考前冲刺笔记
As your IGCSE OCR Chemistry exam approaches, this concise guide covers the essential facts, formulas, and common pitfalls you need to recall. Use it to check understanding of each topic, reinforce key concepts, and build confidence for Papers 1, 2, 3, and 4.
随着 IGCSE OCR 化学考试的临近，这份简明指南涵盖了您需要记忆的基本事实、公式和常见易错点。用它来检查每个主题的理解程度，巩固关键概念，并为试卷 1、2、3 和 4 树立信心。
1. Atomic Structure & The Periodic Table | 原子结构与元素周期表
Atoms are the smallest particles of an element that can take part in chemical reactions. They consist of a central nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The number of protons defines the atomic number and determines the element.
原子是能参与化学反应的元素的最小粒子。它们由含有质子和中子的中心原子核以及按电子层排列的电子组成。质子数定义了原子序数并决定了元素种类。
Relative masses are: proton = 1, neutron = 1, electron = 1/1840. The mass number is the sum of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons, hence different mass numbers.
相对质量：质子 = 1，中子 = 1，电子 = 1/1840。质量数是质子数与中子数之和。同位素是同一元素中中子数不同、因而质量数不同的原子。
Electron shell filling order is 2,8,8 for the first 20 elements. Group number equals the number of outer‑shell electrons. Period number gives the number of occupied shells. Elements in the same group have similar chemical properties because they have the same number of outer electrons.
前 20 号元素的电子层填充顺序为 2,8,8。族数等于最外层电子数。周期数表示已占据的电子层数。同一族元素具有相似的化学性质，因为它们的最外层电子数相同。
Group 1 alkali metals are soft, highly reactive with water, producing hydrogen and a metal hydroxide. Reactivity increases down the group because the outer electron is farther from the nucleus and more easily lost.
第 1 族碱金属质地柔软，与水剧烈反应，生成氢气和金属氢氧化物。向下反应活性增强，因为最外层电子离核更远，更容易失去。
Group 7 halogens are diatomic non‑metals, coloured and toxic. Reactivity decreases down the group; a more reactive halogen can displace a less reactive one from its salt solution. Group 0 noble gases are monatomic and chemically inert due to full outer shells.
第 7 族卤素是双原子非金属，有色且有毒。向下反应活性减弱；较活泼的卤素能从其盐溶液中置换出较不活泼的卤素。第 0 族稀有气体是单原子分子，化学性质稳定，因为最外层已满。
2. Ionic, Covalent & Metallic Bonding | 离子键、共价键与金属键
Ionic bonding occurs between metals and non‑metals via transfer of electrons. Metal atoms lose electrons to form positive cations; non‑metal atoms gain electrons to form negative anions. The oppositely charged ions are held in a giant lattice by strong electrostatic forces.
离子键通过电子转移在金属和非金属之间形成。金属原子失去电子形成阳离子；非金属原子获得电子形成阴离子。带相反电荷的离子通过强静电引力排列在巨型晶格中。
Ionic compounds have high melting and boiling points, are brittle, and conduct electricity when molten or dissolved in water because the ions are free to move. Common examples: NaCl, MgO, CaCl₂.
离子化合物具有高熔点和高沸点、质脆，并且在熔融或溶于水时能够导电，因为离子可以自由移动。常见例子：NaCl、MgO、CaCl₂。
Covalent bonding involves sharing pairs of electrons between non‑metal atoms. Simple molecular substances such as H₂O, CO₂, NH₃ have low melting points and poor electrical conductivity because intermolecular forces are weak and there are no free charged particles.
共价键涉及非金属原子之间共享电子对。简单分子物质，如 H₂O、CO₂、NH₃，熔沸点低且导电性差，因为分子间作用力弱且没有自由带电粒子。
Giant covalent structures (diamond, graphite, silicon dioxide) have very high melting points. Diamond has a tetrahedral structure with each carbon atom bonded to four others; graphite has layers of hexagonally arranged carbon that can slide over each other and contains delocalised electrons, allowing electrical conductivity.
巨型共价结构（金刚石、石墨、二氧化硅）的熔点极高。金刚石具有四面体结构，每个碳原子与另外四个碳原子成键；石墨具有六边形排列的碳层，层间可以滑动，并含有离域电子，因而能导电。
Metallic bonding is the attraction between a regular lattice of positive metal ions and a sea of delocalised electrons. This explains malleability, ductility, and high electrical and thermal conductivity. Alloys are harder than pure metals because different‑sized atoms disrupt the layers, preventing them from sliding.
金属键是规则排列的正金属离子与离域电子海之间的吸引力。这解释了延展性、可锻性以及高导电导热性。合金比纯金属更硬，因为大小不同的原子破坏了层结构，阻止层间滑动。
3. Formulae, Equations & The Mole | 化学式、方程式与摩尔
Always remember to write correct formulae using valency. Use the criss‑cross method: e.g. aluminium oxide: Al³⁺ and O²⁻ gives Al₂O₃. Balance symbol equations by placing coefficients in front, never changing subscripts.
务必使用化合价正确书写化学式。使用十字交叉法：如氧化铝：Al³⁺ 和 O²⁻ 得到 Al₂O₃。通过在前面放置系数来配平符号方程式，绝不能改变化合价下标。
The mole is the unit for amount of substance. One mole contains 6.02 × 10²³ particles (Avogadro constant). The molar mass (g/mol) is the relative atomic or formula mass in grams.
摩尔是物质数量的单位。1 摩尔含有 6.02 × 10²³ 个粒子（阿伏伽德罗常数）。摩尔质量（g/mol）是以克为单位的相对原子质量或式量。
Number of moles = mass (g) ÷ molar mass (g/mol)
摩尔数 = 质量 (g) ÷ 摩尔质量 (g/mol)
For gases at room temperature and pressure (rtp), one mole occupies 24 dm³ (or 24 000 cm³). Use: volume of gas (dm³) = moles × 24. For solutions: concentration (mol/dm³) = moles ÷ volume (dm³).
对于室温常压下的气体，1 摩尔占据 24 dm³（或 24 000 cm³）。使用：气体体积 (dm³) = 摩尔数 × 24。对于溶液：浓度 (mol/dm³) = 摩尔数 ÷ 体积 (dm³)。
In titrations, mole ratios from the balanced equation allow you to calculate an unknown concentration. Remember to convert cm³ to dm³ by dividing by 1000. Percentage yield = (actual yield ÷ theoretical yield) × 100%.
在滴定中，利用配平方程式中的摩尔比可以计算未知浓度。记住将 cm³ 转换为 dm³，除以 1000。产率 = (实际产量 ÷ 理论产量) × 100%。
4. Acids, Bases & Salts | 酸、碱与盐
Acids are proton donors. When dissolved in water, they release H⁺ ions. Common laboratory acids: HCl, H₂SO₄, HNO₃. Bases are proton acceptors and metal oxides or hydroxides. Alkalis are soluble bases that release OH⁻ ions in water.
酸是质子给体。溶于水时释放 H⁺ 离子。常见的实验室酸：HCl、H₂SO₄、HNO₃。碱是质子受体，是金属氧化物或氢氧化物。可溶性碱在水溶液中释放 OH⁻ 离子，称为碱溶液。
Neutralisation: H⁺ + OH⁻ → H₂O. Acid + metal oxide/hydroxide → salt + water. Acid + carbonate → salt + water + CO₂. Acid + metal → salt + hydrogen (except for unreactive metals).
中和反应：H⁺ + OH⁻ → H₂O。酸 + 金属氧化物/氢氧化物 → 盐 + 水。酸 + 碳酸盐 → 盐 + 水 + CO₂。酸 + 金属 → 盐 + 氢气（不活泼金属除外）。
Making soluble salts: Use titration (for Group 1/ammonium salts) or excess insoluble base/metal/carbonate followed by filtration and crystallisation. The pH scale ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 neutral.
制备可溶性盐：使用滴定法（对于第一族/铵盐），或使用过量的不溶性碱/金属/碳酸盐，随后过滤和结晶。pH 值范围从 0（强酸性）到 14（强碱性），7 为中性。
Strong acids completely ionise in water (e.g. HCl, HNO₃, H₂SO₄); weak acids partially ionise (e.g. ethanoic acid CH₃COOH). Solubility rules are essential for predicting precipitates in double displacement reactions.
强酸在水中完全电离（如 HCl、HNO₃、H₂SO₄）；弱酸部分电离（如乙酸 CH₃COOH）。溶解度规则对于预测复分解反应中的沉淀至关重要。
| Soluble Compounds | Exceptions |
|---|---|
| All Na⁺, K⁺, NH₄⁺ salts | None |
| All nitrates | None |
| Most chlorides | AgCl, PbCl₂ (sparingly) |
| Most sulfates | BaSO₄, PbSO₄, CaSO₄ |
| Most carbonates/hydroxides | Sodium, potassium, ammonium |
5. Electrolysis | 电解
Electrolysis uses direct current to drive a non‑spontaneous decomposition of an ionic compound. The electrolyte is the molten or dissolved ionic substance. The cathode (negative electrode) attracts cations where reduction occurs; the anode (positive electrode) attracts anions where oxidation occurs. Remember OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons.
电解使用直流电推动离子化合物的非自发分解。电解质是熔融或溶解的离子化合物。阴极（负极）吸引阳离子，发生还原反应；阳极（正极）吸引阴离子，发生氧化反应。记住：氧化失电子，还原得电子。
In electrolysis of molten binary salts, the metal is produced at the cathode and the non‑metal at the anode. In aqueous solutions, the products depend on the relative reactivity of the ions and the concentration. For example, with dilute NaCl(aq): H₂ at cathode, O₂ at anode; with concentrated brine (NaCl(aq)): H₂ at cathode, Cl₂ at anode.
在熔融二元盐的电解中，阴极析出金属，阳极析出非金属。在水溶液中，产物取决于离子的相对反应活性和浓度。例如，稀 NaCl 溶液：阴极产生 H₂，阳极产生 O₂；浓盐水：阴极 H₂，阳极 Cl₂。
When copper electrodes are used in aqueous CuSO₄, the anode dissolves (Cu → Cu²⁺ + 2e⁻) and pure copper plates onto the cathode. In electroplating, the object to be plated is the cathode and the coating metal is the anode.
当在 CuSO₄ 水溶液中使用铜电极时，阳极溶解（Cu → Cu²⁺ + 2e⁻），纯铜镀覆在阴极上。在电镀中，待镀物体为阴极，镀层金属为阳极。
Half equations are required to show electron transfer. E.g. at the cathode: 2H⁺ + 2e⁻ → H₂; at the anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻.
需要写出半反应式来表示电子转移。例如，阴极：2H⁺ + 2e⁻ → H₂；阳极：4OH⁻ → O₂ + 2H₂O + 4e⁻。
6. Energy Changes in Reactions | 反应中的能量变化
Exothermic reactions transfer energy to the surroundings, causing a temperature rise (e.g. combustion, neutralisation). Endothermic reactions absorb energy from the surroundings, lowering temperature (e.g. thermal decomposition, photosynthesis).
放热反应向环境释放能量，导致温度升高（如燃烧、中和反应）。吸热反应从环境吸收能量，使温度降低（如热分解、光合作用）。
Energy level diagrams show reactants lower than products for endothermic, and higher for exothermic. The energy change ΔH is negative for exothermic and positive for endothermic. Bond breaking is endothermic; bond making is exothermic.
能级图显示：吸热反应中反应物能量低于生成物，放热反应则相反。放热反应的焓变 ΔH 为负，吸热为正。断键吸热，成键放热。
ΔH = total energy absorbed for bond breaking − total energy released for bond making
ΔH = 断键吸收的总能量 − 成键释放的总能量
Calculate ΔH using average bond energies. A negative ΔH confirms the reaction is exothermic overall. Activation energy is the minimum energy needed for colliding particles to react. Catalysts lower activation energy, providing an alternative reaction pathway.
利用平均键能计算 ΔH。ΔH 为负值确认反应整体放热。活化能是碰撞粒子发生反应所需的最小能量。催化剂通过提供另一反应途径来降低活化能。
7. Rates of Reaction & Equilibrium | 反应速率与平衡
The rate of a reaction depends on collision frequency and the fraction of collisions with sufficient energy (activation energy). Factors that increase rate: higher concentration (or pressure for gases), larger surface area of solids, higher temperature, and presence of a catalyst.
反应速率取决于碰撞频率和具有足够能量（活化能）的碰撞比例。能提高速率的因素：更高浓度（或气体压强）、固体更大的表面积、更高温度以及催化剂的存在。
Concentration and surface area increase the number of reacting particles per unit volume. Temperature increases both collision frequency and the proportion of particles with energy ≥ activation energy. Catalysts provide an alternate lower‑energy pathway without being used up.
浓度和表面积增加了单位体积内的反应粒子数量。温度既增加了碰撞频率，又提高了能量 ≥ 活化能的粒子比例。催化剂提供具有更低活化能的替代途径，自身不被消耗。
Reversible reactions reach a dynamic equilibrium when the forward and backward rates are equal, in a closed system. The position of equilibrium can be shifted by changing conditions (Le Chatelier’s Principle).
当正逆反应速率相等时，可逆反应在封闭体系中达到动态平衡。平衡位置可通过改变条件（勒夏特列原理）来移动。
Increasing temperature favours the endothermic direction. Increasing pressure favours the side with fewer gas molecules. Adding a catalyst does not change the equilibrium position; it only speeds up both forward and backward reactions equally.
升高温度有利于吸热方向。增大压强有利于气体分子数较少的一侧。添加催化剂不改变平衡位置；它只同等加快正逆反应速率。
For the Haber process (N₂ + 3H₂ ⇌ 2NH₃, exothermic), optimum conditions are around 450 °C (compromise between rate and yield), 200 atm pressure, and an iron catalyst.
对于哈伯法（N₂ + 3H₂ ⇌ 2NH₃，放热），最佳条件是约 450 °C（速率与产率的折衷）、200 atm 压强以及铁催化剂。
8. Organic Chemistry | 有机化学
Crude oil is a mixture of hydrocarbons separated by fractional distillation. Fractions are separated based on boiling points, which depend on chain length. Shorter hydrocarbons have lower boiling points and are more flammable.
原油是烃的混合物，通过分馏进行分离。馏分根据沸点分离，沸点取决于碳链长度。较短的烃沸点较低且更易燃。
Alkanes (CₙH₂ₙ₊₂) are saturated hydrocarbons. They undergo complete combustion to produce CO₂ and H₂O, and substitution reaction with halogens in the presence of UV light. Alkenes (CₙH₂ₙ) contain a C=C double bond and are unsaturated; they decolourise bromine water, used as a test.
烷烃（CₙH₂ₙ₊₂）是饱和烃。它们完全燃烧生成 CO₂ 和 H₂O，并在紫外光下与卤素发生取代反应。烯烃（CₙH₂ₙ）含有 C=C 双键，属于不饱和烃；它们能使溴水褪色，可用于检验。
Alkenes undergo addition reactions: with hydrogen (hydrogenation), with water (hydration to make alcohols), and with halogens. Addition polymerisation forms polymers such as poly(ethene) and poly(propene).
烯烃发生加成反应：与氢气（氢化）、与水（水合生成醇）、与卤素。加成聚合形成聚合物，如聚乙烯和聚丙烯。
Alcohols contain the –OH functional group. Methanol, ethanol, propanol burn well, are used as solvents and fuels. Ethanol can be made by fermentation (using yeast, 30–40 °C, anaerobic) or by hydration of ethene (high temperature, catalyst). Carboxylic acids contain the –COOH group; ethanoic acid is a weak acid, forms esters with alcohols.
醇含有 –OH 官能团。甲醇、乙醇、丙醇燃烧性能好，用作溶剂和燃料。乙醇可通过发酵（酵母，30–40 °C，厌氧）或乙烯水合（高温、催化剂）制得。羧酸含有 –COOH 基团；乙酸是弱酸，与醇反应生成酯。
Esters have the functional group –COO–, are volatile with fruity smells, and used in flavourings and perfumes. They are made by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst.
酯的官能团为 –COO–，具有果香气味且易挥发，用于调味剂和香水。由羧酸与醇在酸催化下反应制得。
9. Chemical Analysis & Purity | 化学分析与纯度
A pure substance has a fixed, sharp melting and boiling point. Impurities lower the melting point and widen the melting range. A formulation is a mixture designed as a useful product with precise proportions.
纯物质具有固定、敏锐的熔点和沸点。杂质会降低熔点并使熔程变宽。配方是按精确比例设计的有用产品。
Chromatography separates mixtures based on solubility in a mobile phase. Retention factor Rf = distance moved by substance ÷ distance moved by solvent front. It is constant for a particular substance under specified conditions.
色谱法根据各组分在流动相中的溶解度分离混合物。比移值 Rf = 物质移动距离 ÷ 溶剂前沿移动距离。特定物质在特定条件下 Rf 值为常数。
Flame tests identify metal cations: Li⁺ (red), Na⁺ (yellow), K⁺ (lilac), Ca²⁺ (orange‑red), Cu²⁺ (green). Addition of sodium hydroxide solution produces coloured precipitates: Cu²⁺ (blue), Fe²⁺ (green), Fe³⁺ (brown). Al³⁺ and Ca²⁺ give white precipitates; further addition of NaOH dissolves the aluminium hydroxide precipitate.
焰色反应鉴别金属阳离子：Li⁺（红）、Na⁺（黄）、K⁺（紫）、Ca²⁺（橙红）、Cu²⁺（绿）。加入氢氧化钠溶液产生有色沉淀：Cu²⁺（蓝）、Fe²⁺（绿）、Fe³⁺（棕）。Al³⁺ 和 Ca²⁺ 产生白色沉淀；再加入 NaOH，氢氧化铝沉淀溶解。
| Anion | Test | Positive result |
|---|---|---|
| Carbonate CO₃²⁻ | Add dilute acid, bubble gas through limewater | Limewater turns milky |
| Sulfate SO₄²⁻ | Add HCl then BaCl₂ solution | White precipitate |
| Halide Cl⁻, Br⁻, I⁻ | Add HNO₃ then AgNO₃ solution | White (Cl⁻), cream (Br⁻), yellow (I⁻) |
Instrumental methods such as flame emission spectroscopy can be used to identify ions rapidly and accurately. They provide quantitative data and are more sensitive than traditional tests.
仪器分析方法如火焰发射光谱可以快速、准确地识别离子。它们提供定量数据，比传统测试更灵敏。
10. Practical Skills & Common Mistakes | 实验技能与常见错误
When measuring volume, always read the bottom of the meniscus at eye level. Use a burette for titrations to 0.05 cm³ precision. A pipette delivers a fixed volume with high accuracy.
测量体积时，始终在视线水平处读取弯月面底部。滴定中使用滴定管，精度可达 0.05 cm³。移液管可以高精度地量取固定体积。
In rate experiments, measure either the volume of gas produced over time or the change in mass. Plot graphs of volume/mass against time; the initial gradient gives the rate. For temperature investigations, allow reactants to reach thermal equilibrium before mixing.
在速率实验中，测量随时间产生的气体体积或质量变化。绘制体积/质量对时间的图；初始梯度代表反应速率。在温度研究实验中，混合前让反应物达到热平衡。
Always state units in calculations and give answers to the appropriate number of significant figures. Check that symbol equations are balanced before performing mole calculations. Avoid confusion between concentration (mol/dm³) and number of moles (mol).
计算时始终写明单位，并将答案保留适当有效数字。在进行摩尔计算前，检查符号方程式是否配平。避免混淆浓度（mol/dm³）和摩尔数（mol）。
Common error: in electrolysis prediction, forgetting that in aqueous solutions both the cation and the water‑derived H⁺ compete at the cathode. For reactive metals like sodium, hydrogen gas is produced instead of the metal.
常见错误：在电解预测中，忘记水溶液中阳离子与由水产生的 H⁺ 都在阴极竞争。对于活泼金属如钠，会生成氢气而不是金属。
In organic chemistry, be particular about the condition of reactions. Fermentation requires yeast and an anaerobic environment, whereas hydration of ethene needs a phosphoric acid catalyst and steam under high pressure. Do not confuse addition polymerisation with condensation polymerisation, which is not required at IGCSE.
在有机化学中，特别注意反应条件。发酵需要酵母和厌氧环境，而乙烯水合需要磷酸催化剂和高压水蒸气。不要将加成聚合与缩合聚合混淆，后者不在 IGCSE 要求范围内。
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