📚 Year 8 CAIE Chemistry: Formula & Theorem Quick Reference Guide | Year 8 CAIE 化学：公式定理速查手册
This handbook compiles all the essential formulas, equations, balancing rules, and key principles you will meet in the Year 8 CAIE Chemistry course. It is designed for quick revision – keep it handy while solving past papers or checking your notes.
本手册汇编了 Year 8 CAIE 化学课程中的所有核心公式、方程式、配平规则和重要原理，专为快速复习而设计。在做真题或整理笔记时，把它放在手边吧。
1. Relative Atomic Mass (Ar) & Relative Molecular Mass (Mr) | 相对原子质量 (Ar) 与相对分子质量 (Mr)
Relative atomic mass (Ar) compares the average mass of an atom of an element to 1/12 of the mass of one carbon‑12 atom. Since it is a ratio, Ar has no unit.
相对原子质量 (Ar) 是将元素的平均原子质量与一个碳‑12 原子质量的 1/12 进行比较。由于是比值，Ar 没有单位。
Ar = (average mass of one atom of the element) ÷ (1/12 × mass of one carbon‑12 atom)
Relative molecular mass (Mr) is the sum of the relative atomic masses of all the atoms in a molecule. It is also a ratio without a unit.
相对分子质量 (Mr) 是一个分子中所有原子的相对原子质量之和。它同样是一个比值，没有单位。
Mr = sum of Ar of every atom in the molecule
Example: Mr of H₂O = (2 × 1) + 16 = 18. Mr of CO₂ = 12 + (2 × 16) = 44.
示例：H₂O 的 Mr = (2 × 1) + 16 = 18。CO₂ 的 Mr = 12 + (2 × 16) = 44。
2. Writing Chemical Formulae (Cross‑Multiplication Method) | 书写化学式（交叉化合价法）
Chemical formulae are written by swapping the valencies (combining powers) of the ions or atoms and dropping the signs. The valency tells you how many electrons an atom loses, gains or shares.
化学式通过交换离子或原子的化合价（化合能力）并省略符号来书写。化合价告诉你一个原子失去、得到或共享多少个电子。
Step 1: Write the symbols of the ions, with the charge top right. Step 2: Cross the numbers (ignoring + or –) down to the opposite bottom corner. Step 3: Reduce the ratio to the simplest whole numbers if possible.
第1步：写出离子的符号，将电荷写在右上角。第2步：将数字（忽略正负号）交叉到对方离子的右下角。第3步：如果可能，将比例化简为最简整数。
| Na⁺ and Cl⁻ | NaCh; → NaCl |
| Ca²⁺ and O²⁻ | CaO (charges 2 and 2 cancel) |
| Al³⁺ and O²⁻ | Al₂O₃ |
| Mg²⁺ and NO₃⁻ | Mg(NO₃)₂ |
For molecular (covalent) compounds, we use the prefixes mono‑, di‑, tri‑ etc. However, many simple covalent names follow valency rules, e.g. carbon dioxide CO₂.
对于分子（共价）化合物，我们使用前缀一、二、三等。不过，许多简单共价化合物的命名也遵循化合价规则，例如二氧化碳 CO₂。
3. Balancing Chemical Equations & Law of Conservation of Mass | 配平化学方程式与质量守恒定律
The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction. Therefore, the number of each type of atom must be the same on both sides of the equation.
质量守恒定律指出，物质在化学反应中既不能被创造也不能被消灭。因此，每种原子的数目在方程式两边必须相等。
Total mass of reactants = Total mass of products
To balance an equation, place large numbers (coefficients) in front of the chemical formulae. Never change the small subscript numbers inside a formula.
配平方程式时，在化学式前面放置大数字（系数）。切勿更改化学式内部的小下标数字。
Example: H₂ + O₂ → H₂O (unbalanced) → 2H₂ + O₂ → 2H₂O (balanced). Always add state symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution.
示例：H₂ + O₂ → H₂O（未配平）→ 2H₂ + O₂ → 2H₂O（已配平）。记得添加状态符号：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液。
4. Calculating Reacting Masses from Equations | 根据方程式计算反应物质量
Once the equation is balanced, you can use the concept of relative mass (Mr) to work out the actual masses of substances that react and are produced.
一旦方程式配平，你就可以利用相对质量（Mr）的概念来计算参与反应和生成的物质的实际质量。
l relative mass of A in equation / total relative mass of B in equation) × mass of B
If 48 g of magnesium reacts fully with 32 g of oxygen to make magnesium oxide (2Mg + O₂ → 2MgO), the mass of MgO produced must be 48 + 32 = 80 g.
如果 48 g 镁与 32 g 氧气充分反应生成氧化镁（2Mg + O₂ → 2MgO），则生成的 MgO 质量必定是 48 + 32 = 80 g。
To find an unknown mass, first write the balanced equation, work out the relative masses for the two substances, and set up a proportion using the coefficients.
要找出未知质量，先写出配平方程式，计算这两种物质的相对质量，然后利用化学计量数建立比例关系。
5. Rate of Reaction Calculations | 反应速率计算
The rate of a chemical reaction tells you how quickly a reactant is used up or a product is formed. It is usually measured over a time interval.
化学反应速率表示反应物被消耗或产物生成的速度快慢。通常在一个时间间隔内进行测量。
Average rate of reaction = change in amount (mass, volume or concentration) / time taken
Units can be g/s, cm³/s or g/min. For a reaction producing gas, you might record the volume of gas every 30 seconds and calculate the rate for each interval.
单位可以是 g/s、cm³/s 或 g/min。对于产生气体的反应，可以每 30 秒记录一次气体体积，并计算每个时间段的速率。
Factors that affect the rate (temperature, concentration, surface area, catalysts) do not alter the mass‑balance formula, but they change the value of the rate.
影响速率的因素（温度、浓度、表面积、催化剂）不会改变质量守恒公式，但会改变速率的大小。
6. Concentration Calculations | 浓度计算
Concentration describes how much solute is dissolved in a given amount of solvent or solution. In Year 8 we use two common ways:
浓度描述在给定量的溶剂或溶液中有多少溶质被溶解。在 Year 8 我们常用两种表示方法：
Mass percentage % = (mass of solute / mass of solution) × 100%
Mass concentration (g/dm³) = mass of solute (g) / volume of solution (dm³)
Remember: 1 dm³ = 1000 cm³. To covert a volume in cm³ to dm³, divide by 1000. For example, 250 cm³ = 0.25 dm³.
记住：1 dm³ = 1000 cm³。将体积从 cm³ 换算为 dm³，需除以 1000。例如 250 cm³ = 0.25 dm³。
7. pH Scale & Acid‑Base Indicators | pH 标度与酸碱指示剂
The pH scale (0–14) measures how acidic or alkaline a solution is. Universal indicator turns different colours across the full range.
pH 标度（0–14）衡量溶液的酸碱度。通用指示剂在整个范围内呈现不同的颜色。
- pH < 7 – acidic (red, orange, yellow)
- pH = 7 – neutral (green)
- pH > 7 – alkaline (blue, violet, purple)
- pH < 7 – 酸性（红、橙、黄）
- pH = 7 – 中性（绿）
- pH > 7 – 碱性（蓝、紫、深紫）
Litmus paper turns red in acid and blue in alkali. Phenolphthalein is colourless in acid and pink in alkali.
石蕊试纸遇酸变红，遇碱变蓝。酚酞在酸性溶液中无色，在碱性溶液中呈粉红色。
8. Reactivity Series & Displacement Reactions | 金属活动性顺序与置换反应
A more reactive metal can displace a less reactive metal from its compound. The reactivity series for common metals is:
较活泼的金属能将较不活泼的金属从其化合物中置换出来。常见金属的活动性顺序为：
K > Na > Ca > Mg > Al > Zn > Fe > (H) > Cu > Ag > Au
All metals above hydrogen can react with dilute acids to produce hydrogen gas. A displacement reaction only occurs if the free metal sits higher on the series than the metal in the compound.
排在氢之前的金属都能与稀酸反应产生氢气。只有当游离金属在活动性顺序表中的位置高于化合物中的金属时，置换反应才会发生。
Examples: Zn + CuSO₄ → ZnSO₄ + Cu (zinc displaces copper). Cu + ZnSO₄ → no reaction (copper is less reactive).
示例：Zn + CuSO₄ → ZnSO₄ + Cu（锌置换铜）。Cu + ZnSO₄ → 无反应（铜不活泼）。
9. States of Matter & Kinetic Particle Theory | 物质状态与粒子动力学理论
The kinetic particle theory states that all matter is made of tiny particles that are constantly moving. The amount of movement and the arrangement change with state.
粒子动力学理论指出，所有物质都由不断运动着的微小粒子组成。运动程度和排列方式随状态而变化。
- Solid: particles vibrate in fixed positions, held by strong forces. Fixed shape and volume.
- Liquid: particles move past each other, forces are weaker. Fixed volume but takes the shape of the container.
- Gas: particles move rapidly in all directions, very weak forces. No fixed shape or volume.
- 固体：粒子在固定位置上振动，粒子间作用力强。有固定的形状和体积。
- 液体：粒子相互滑动，作用力较弱。体积固定，但形状随容器而定。
- 气体：粒子在所有方向快速运动，作用力非常弱。没有固定的形状和体积。
Changes of state (melting, boiling, freezing, condensing) are physical changes, not chemical ones. Mass is conserved during any change of state.
状态变化（熔化、沸腾、凝固、冷凝）属于物理变化而非化学变化。质量在任何状态变化中都保持不变。
10. Separation Techniques – Key Principles | 分离技术 – 关键原理
Mixtures can be separated based on differences in physical properties. The main techniques and their working principles are:
混合物可根据物理性质的差异进行分离。主要技术及其工作原理包括：
| Filtration | Separates insoluble solid from liquid based on particle size. |
| Evaporation | Removes solvent by heating, leaving dissolved solid behind. |
| Distillation | Separates a solvent from a solution by boiling and condensing. |
| Chromatography | Separates dissolved substances by different solubility and adhesion. |
| 过滤 | 利用颗粒大小将不溶性固体与液体分离。 |
| 蒸发 | 加热除去溶剂，留下溶解的固体。 |
| 蒸馏 | 通过沸腾和冷凝将溶剂从溶液中分离出来。 |
| 色谱法 | 利用溶解度和吸附力的差异分离溶解物质。 |
When choosing a technique, always identify whether the substances are solid, liquid or dissolved first.
选择分离方法时，务必先判断混合物中的物质是固体、液体还是已溶解。
11. Atomic Structure & Electronic Configuration | 原子结构与电子排布
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The key numbers are linked by these two equations:
原子由包含质子和中子的原子核以及核外分层排布的电子组成。关键数字由以下两个等式关联：
Atomic number (Z) = number of protons = number of electrons (in a neutral atom)
Mass number (A) = number of protons + number of neutrons
Electrons occupy shells around the nucleus. The first shell holds up to 2 electrons, the second up to 8, and the third up to 8 (for the first 20 elements).
电子在原子核外的壳层中排布。第一层最多容纳 2 个电子，第二层最多容纳 8 个，第三层最多容纳 8 个（适用于前 20 号元素）。
Example: Sodium (Na), atomic number 11: electronic configuration 2,8,1. Chlorine (Cl), atomic number 17: electronic configuration 2,8,7.
示例：钠 (Na)，原子序数 11，电子排布 2,8,1。氯 (Cl)，原子序数 17，电子排布 2,8,7。
12. Ionic Bonding & Formulae of Ionic Compounds | 离子键与离子化合物化学式
Ionic bonding occurs when a metal atom transfers electrons to a non‑metal atom. The metal becomes a positive ion (cation) and the non‑metal becomes a negative ion (anion). The oppositely charged ions attract each other strongly – this is the ionic bond.
离子键形成于金属原子将电子转移给非金属原子之时。金属变成阳离子（正离子），非金属变成阴离子（负离子）。带相反电荷的离子相互强烈吸引，这就是离子键。
The formula of an ionic compound must be neutral overall. We use the charges on the ions to construct the formula by balancing the total positive and total negative charges.
离子化合物的化学式必须整体呈电中性。我们利用离子的电荷，通过平衡正负电荷总数来构建化学式。
Total positive charge + Total negative charge = 0
Examples: Na⁺ and Cl⁻ give NaCl (one of each). Ca²⁺ and Cl⁻ give CaCl₂ (one Ca²⁺ needs two Cl⁻). Mg²⁺ and O²⁻ give MgO (charges cancel).
示例：Na⁺ 与 Cl⁻ 组成 NaCl（各一个）。Ca²⁺ 与 Cl⁻ 组成 CaCl₂（一个 Ca²⁺ 需要两个 Cl⁻）。Mg²⁺ 与 O²&#x
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