📚 Acids and Alkalis: KS3 CIE Chemistry Essentials | 酸与碱：KS3 CIE 化学核心要点
Acids and alkalis are two important groups of chemicals that you meet every day, from the citric acid in lemons to the alkaline cleaning products used at home. Understanding their properties, how to test them, and how they react together forms a key part of the KS3 CIE Chemistry course.
酸和碱是你在日常生活中经常遇到的两类重要化学物质，从柠檬中的柠檬酸到家中使用的碱性清洁产品。理解它们的性质、如何检测它们以及它们如何相互反应，是 KS3 CIE 化学课程的关键部分。
1. What Are Acids and Alkalis? | 什么是酸和碱？
An acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. These hydrogen ions give acids their characteristic sour taste and their ability to react with certain metals and bases.
酸是一种溶于水时会释放氢离子（H⁺）的物质。这些氢离子使酸具有特征的酸味，并使其能够与某些金属和碱发生反应。
An alkali is a soluble base that releases hydroxide ions (OH⁻) when dissolved in water. Alkalis feel soapy and can neutralise acids. Common laboratory alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH).
碱是一种可溶性碱，溶于水时会释放氢氧根离子（OH⁻）。碱摸起来有滑腻感，能中和酸。实验室中常见的碱包括氢氧化钠（NaOH）和氢氧化钾（KOH）。
2. Everyday Examples of Acids and Alkalis | 日常生活中的酸和碱
Acids are found in many foods and drinks. Citrus fruits contain citric acid, vinegar contains ethanoic acid, and fizzy drinks often contain carbonic acid. Tea and coffee are also mildly acidic.
酸存在于许多食物和饮料中。柑橘类水果含有柠檬酸，醋含有乙酸，汽水通常含有碳酸。茶和咖啡也呈弱酸性。
Alkalis are commonly found in cleaning products. Soap, bleach, oven cleaner and drain cleaner are alkaline because alkalis are good at breaking down grease and dirt. Indigestion tablets are also alkaline to neutralise excess stomach acid.
碱常见于清洁产品中。肥皂、漂白剂、烤箱清洁剂和下水道清洁剂都是碱性的，因为碱能很好地分解油脂和污垢。消化片也是碱性的，用于中和多余的胃酸。
3. Using Indicators | 使用指示剂
An indicator is a substance that changes colour depending on whether it is in an acidic, neutral, or alkaline solution. Indicators allow us to test whether an unknown solution is an acid or an alkali.
指示剂是一种会根据溶液呈酸性、中性还是碱性而改变颜色的物质。指示剂使我们能够检测未知溶液是酸还是碱。
Litmus is a common indicator. Blue litmus paper turns red in acids, while red litmus paper turns blue in alkalis. In neutral solutions, litmus paper keeps its original colour.
石蕊是一种常见的指示剂。蓝色石蕊试纸在酸性溶液中变红，而红色石蕊试纸在碱性溶液中变蓝。在中性溶液中，石蕊试纸保持原来的颜色。
Phenolphthalein is another indicator often used in titrations. It is colourless in acidic and neutral solutions, but turns pink in alkaline solutions.
酚酞是另一种常用于滴定实验的指示剂。它在酸性和中性溶液中为无色，但在碱性溶液中变为粉红色。
4. The pH Scale | pH 标度
The pH scale is a numerical scale from 0 to 14 that measures how acidic or alkaline a solution is. A pH value below 7 indicates an acidic solution, pH 7 is neutral, and a pH above 7 indicates an alkaline solution.
pH 标度是一个从 0 到 14 的数值标度，用于衡量溶液的酸性或碱性程度。pH 值低于 7 表示溶液为酸性，pH 等于 7 为中性，pH 高于 7 表示溶液为碱性。
The lower the pH, the more strongly acidic the solution. For example, stomach acid has a pH of about 1-2, while lemon juice has a pH of about 2-3. Pure water has a pH of 7, and household ammonia has a pH of about 11-12.
pH 值越低，溶液的酸性越强。例如，胃酸的 pH 值约为 1-2，而柠檬汁的 pH 值约为 2-3。纯水的 pH 值为 7，家用氨水的 pH 值约为 11-12。
Universal indicator is a mixture of dyes that shows a range of colours at different pH values. It can be used as a solution or on paper strips to estimate the pH of a substance.
通用指示剂是多种染料的混合物，在不同 pH 值下会显示一系列颜色。它可以作为溶液或试纸条使用，用于估计物质的 pH 值。
5. Neutralisation Reactions | 中和反应
Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. The hydrogen ions from the acid react with the hydroxide ions from the alkali to form water.
中和反应是酸与碱（或可溶性碱）反应生成盐和水的反应。来自酸的氢离子与来自碱的氢氧根离子反应生成水。
The general word equation for neutralisation is:
中和反应的一般文字方程式为：
acid + alkali → salt + water
酸 + 碱 → 盐 + 水
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
盐酸 + 氢氧化钠 → 氯化钠 + 水
Neutralisation reactions are exothermic, which means they release heat energy. This is why you may notice a temperature rise when an acid and an alkali are mixed in the correct proportions.
中和反应是放热反应，这意味着它们会释放热能。这就是为什么当酸和碱以正确比例混合时，你可能会注意到温度升高。
6. Acids and Metals | 酸与金属的反应
Dilute acids react with certain metals, such as magnesium, zinc and iron, to produce a salt and hydrogen gas. The general word equation is:
稀酸会与某些金属（如镁、锌和铁）反应，生成盐和氢气。一般文字方程式为：
acid + metal → salt + hydrogen
酸 + 金属 → 盐 + 氢气
For example, hydrochloric acid reacts with magnesium to form magnesium chloride and hydrogen gas:
例如，盐酸与镁反应生成氯化镁和氢气：
2HCl + Mg → MgCl₂ + H₂
盐酸 + 镁 → 氯化镁 + 氢气
Hydrogen gas can be tested using a burning splint. If hydrogen is present, the gas burns with a squeaky pop sound.
氢气可以用点燃的木条进行检验。如果存在氢气，气体会燃烧并发出 ‘噗’ 的爆鸣声。
Not all metals react with acids. Copper, for example, does not react with dilute hydrochloric acid because it is less reactive than hydrogen.
并非所有金属都能与酸反应。例如，铜不与稀盐酸反应，因为它的活泼性比氢低。
7. Acids and Carbonates | 酸与碳酸盐的反应
Acids react with carbonates and hydrogencarbonates to produce a salt, water and carbon dioxide gas. The general word equation is:
酸与碳酸盐和碳酸氢盐反应生成盐、水和二氧化碳气体。一般文字方程式为：
acid + carbonate → salt + water + carbon dioxide
酸 + 碳酸盐 → 盐 + 水 + 二氧化碳
For example, hydrochloric acid reacts with calcium carbonate to form calcium chloride, water and carbon dioxide:
例如，盐酸与碳酸钙反应生成氯化钙、水和二氧化碳：
2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
盐酸 + 碳酸钙 → 氯化钙 + 水 + 二氧化碳
Carbon dioxide gas can be tested by bubbling it through limewater. If carbon dioxide is present, the limewater turns cloudy or milky.
二氧化碳气体可以通过将其通入石灰水来检验。如果存在二氧化碳，石灰水会变浑浊或呈乳白色。
8. Bases and Alkalis | 碱与可溶性碱
A base is a substance that can neutralise an acid. Metal oxides and metal hydroxides are common bases. For example, copper(II) oxide (CuO) and calcium hydroxide (Ca(OH)₂) are bases.
碱是能中和酸的物质。金属氧化物和金属氢氧化物是常见的碱。例如，氧化铜（CuO）和氢氧化钙（Ca(OH)₂）都是碱。
An alkali is a base that dissolves in water. All alkalis are bases, but not all bases are alkalis. Sodium hydroxide and potassium hydroxide are alkalis because they are soluble in water, whereas copper(II) oxide is a base but not an alkali.
可溶性碱是溶于水的碱。所有的可溶性碱都是碱，但并非所有的碱都是可溶性碱。氢氧化钠和氢氧化钾是可溶性碱，因为它们溶于水，而氧化铜是碱但不是可溶性碱。
Alkalis produce hydroxide ions (OH⁻) in water. These hydroxide ions are responsible for the alkaline properties, such as turning red litmus blue.
可溶性碱在水中产生氢氧根离子（OH⁻）。这些氢氧根离子决定了碱性性质，例如使红色石蕊试纸变蓝。
9. Making Salts | 盐的生成
A salt is an ionic compound formed when the hydrogen ion of an acid is replaced by a metal ion. The name of the salt depends on the acid used and the metal in the base or metal reactant.
盐是一种离子化合物，当酸中的氢离子被金属离子取代时形成。盐的名称取决于所用的酸和碱或金属反应物中的金属。
Hydrochloric acid produces chloride salts, sulfuric acid produces sulfate salts, and nitric acid produces nitrate salts.
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