📚 KS3 Chemistry Review 6.19: Acids, Alkalis and Neutralisation | KS3 化学复习 6.19：酸、碱与中和反应
This KS3 Chemistry review focuses on acids, alkalis and neutralisation, one of the core units in the Key Stage 3 science curriculum. You will learn how to use the pH scale, identify common acids and alkalis, and write word and symbol equations for neutralisation reactions.
本 KS3 化学复习聚焦酸、碱与中和反应，这是 KS3 科学课程的核心单元之一。你将学习如何使用 pH 标度、识别常见酸和碱，并书写中和反应的文字方程式和符号方程式。
1. What Are Acids and Alkalis? | 什么是酸和碱？
Acids are substances that release hydrogen ions in water, but at KS3 you can think of them as chemicals with a pH lower than 7. They often taste sour and many are corrosive.
酸是在水中释放氢离子的物质，但在 KS3 阶段你可以把它们理解为 pH 值小于 7 的化学物质。它们通常有酸味，许多酸具有腐蚀性。
Alkalis are soluble bases. They feel soapy, have a pH greater than 7, and can also be corrosive. Many household cleaners contain alkalis because they help break down grease and oils.
碱是可溶的碱性物质。它们摸起来有滑腻感，pH 值大于 7，也可能具有腐蚀性。许多家用清洁剂含有碱，因为碱有助于分解油脂。
You must never taste or touch chemicals in the laboratory. Always wear safety goggles when working with acids and alkalis.
在实验室里绝不能品尝或触摸化学药品。接触酸和碱时务必佩戴护目镜。
2. The pH Scale | pH 值标度
The pH scale runs from 0 to 14. A pH of 7 is neutral. Values below 7 are acidic, and values above 7 are alkaline. The further a value is from 7, the stronger the acid or alkali.
pH 标度从 0 到 14。pH 为 7 是中性。低于 7 为酸性，高于 7 为碱性。数值离 7 越远，酸或碱的强度越大。
Universal indicator changes colour depending on pH. The colours are often remembered as a rainbow from red to purple.
通用指示剂会根据 pH 值改变颜色。这些颜色常被记作从红到紫的彩虹色。
| pH range | pH 范围 | Universal indicator colour | 通用指示剂颜色 | Description | 描述 |
|---|---|---|
| 0-2 | Red | 红色 | Strong acid | 强酸 |
| 3-4 | Orange | 橙色 | Weak acid | 弱酸 |
| 5-6 | Yellow | 黄色 | Very weak acid | 极弱酸 |
| 7 | Green | 绿色 | Neutral | 中性 |
| 8-9 | Blue | 蓝色 | Very weak alkali | 极弱碱 |
| 10-11 | Dark blue | 深蓝色 | Weak alkali | 弱碱 |
| 12-14 | Purple | 紫色 | Strong alkali | 强碱 |
3. Common Acids and Alkalis | 常见的酸和碱
Common laboratory acids include hydrochloric acid, sulfuric acid and nitric acid.
常见的实验室酸包括盐酸、硫酸和硝酸。
Household acids include vinegar, which contains ethanoic acid, and citrus fruits, which contain citric acid.
家用酸包括醋（含乙酸）和柑橘类水果（含柠檬酸）。
Common alkalis include sodium hydroxide, potassium hydroxide and ammonia solution. These are often found in cleaning products and laboratory reagents.
常见碱包括氢氧化钠、氢氧化钾和氨水。它们常见于清洁产品和实验室试剂中。
- Hydrochloric acid: HCl | 盐酸：HCl
- Sulfuric acid: H₂SO₄ | 硫酸：H₂SO₄
- Nitric acid: HNO₃ | 硝酸：HNO₃
- Sodium hydroxide: NaOH | 氢氧化钠：NaOH
- Potassium hydroxide: KOH | 氢氧化钾：KOH
- Ammonia solution: NH₃(aq) | 氨水：NH₃(aq)
4. Indicators and Colour Changes | 指示剂与颜色变化
Litmus is a simple indicator. It turns red in acidic solutions and blue in alkaline solutions. It is often used as paper strips rather than a solution.
石蕊是一种简单指示剂。它在酸性溶液中变红，在碱性溶液中变蓝。它通常以纸条形式使用，而非溶液。
Phenolphthalein is colourless in acid and pink in alkali. Universal indicator gives a full range of colours, so it can be used to estimate pH.
酚酞在酸中无色，在碱中呈粉红色。通用指示剂给出完整的颜色范围，因此可用于估计 pH 值。
Red cabbage indicator is a natural indicator that can be made at home. It shows red, purple, blue or green depending on the pH of the solution.
红甘蓝指示剂是一种可以在家制作的天然指示剂。根据溶液的 pH 不同，它显示红、紫、蓝或绿色。
5. Neutralisation | 中和反应
Neutralisation is a reaction between an acid and a base or alkali that produces a salt and water. The general word equation is:
中和反应是酸与碱或碱性物质反应生成盐和水的过程。通用文字方程式为：
acid + alkali → salt + water
For example, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water.
例如，盐酸与氢氧化钠反应生成氯化钠和水。
HCl + NaOH → NaCl + H₂O
Neutralisation reactions are often exothermic, meaning they release heat energy. This can be measured by a temperature rise in the reaction mixture.
中和反应通常是放热反应，即释放热能。这可以通过反应混合物温度升高来测量。
6. Making Salts | 盐的制备
The salt produced depends on the acid and the base used. Hydrochloric acid makes chlorides, sulfuric acid makes sulfates, and nitric acid makes nitrates.
生成的盐取决于所用的酸和碱。盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐。
Insoluble bases such as copper oxide also neutralise acids. For example:
不溶性碱性物质如氧化铜也能中和酸。例如：
CuO + H₂SO₄ → CuSO₄ + H₂O
This reaction makes copper sulfate, a blue salt often used in schools for growing crystals.
该反应生成硫酸铜，一种常用于学校晶体培养实验的蓝色盐。
7. Everyday Neutralisation | 日常生活中的中和反应
Indigestion tablets contain bases such as calcium carbonate
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