📚 Acids, Bases and Salts for CIE IGCSE Chemistry | CIE IGCSE 化学：酸、碱和盐
This revision guide covers the key ideas in the Cambridge IGCSE Chemistry topic of acids, bases and salts. You will learn how to define acids and alkalis, use indicators, predict salt formation, choose a salt preparation method, carry out titrations and test for common gases. The content follows the Core and Extended syllabus for Cambridge IGCSE Chemistry 0620/0971.
本复习指南涵盖剑桥 IGCSE 化学中酸、碱和盐的核心知识点。你将学习如何定义酸和碱、使用指示剂、预测盐的生成、选择制盐方法、进行滴定以及检验常见气体。内容符合 Cambridge IGCSE Chemistry 0620/0971 核心与拓展大纲要求。
1. Definitions of Acids and Bases | 酸和碱的定义
In IGCSE chemistry an acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. For example hydrogen chloride gas dissolves in water to form hydrochloric acid, which contains H⁺ and Cl⁻ ions.
在 IGCSE 化学中，酸是溶于水时释放氢离子（H⁺）的物质。例如氯化氢气体溶于水形成盐酸，溶液中含有 H⁺ 和 Cl⁻ 离子。
A base is a substance that reacts with an acid to form a salt and water. If a base is soluble in water it is called an alkali, and it releases hydroxide ions (OH⁻) in solution. Common alkalis include sodium hydroxide (NaOH) and ammonia solution (NH₃).
碱是与酸反应生成盐和水的物质。可溶于水的碱称为碱溶液（alkali），它在溶液中释放氢氧根离子（OH⁻）。常见的碱溶液包括氢氧化钠（NaOH）和氨水（NH₃）。
You should be able to name common laboratory acids: hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These acids provide the anions Cl⁻, SO₄²⁻ and NO₃⁻ that appear in their salts.
你需要能说出常见实验室酸：盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。这些酸提供了盐中的阴离子 Cl⁻、SO₄²⁻ 和 NO₃⁻。
Remember that not every substance containing hydrogen is an acid. Ethanol contains hydrogen atoms but does not release H⁺ ions in water.
请记住，并非所有含氢的物质都是酸。乙醇含有氢原子，但在水中不会释放 H⁺ 离子。
2. The pH Scale and Indicators | pH 标度与指示剂
The pH scale runs from 0 to 14 and measures how acidic or alkaline a solution is. A pH below 7 is acidic, pH 7 is neutral, and a pH above 7 is alkaline. The lower the pH, the higher the concentration of H⁺ ions.
pH 标度范围为 0 到 14，用于衡量溶液的酸性或碱性。pH 小于 7 为酸性，pH 等于 7 为中性，pH 大于 7 为碱性。pH 越小，H⁺ 离子浓度越高。
Indicators change colour depending on the pH of the solution. Litmus is red in acid and blue in alkali. Methyl orange is red in acid and yellow in alkali, while thymolphthalein is colourless in acid and blue in alkali.
指示剂根据溶液的 pH 改变颜色。石蕊在酸中呈红色，在碱中呈蓝色。甲基橙在酸中呈红色，在碱中呈黄色；百里酚酞在酸中无色，在碱中呈蓝色。
Universal indicator is a mixture of dyes that gives a range of colours across the pH scale, so it can estimate the pH value rather than just saying acidic or alkaline.
通用指示剂是多种染料的混合物，在 pH 标度上呈现一系列颜色，因此它可以估算 pH 值，而不仅仅判断酸性或碱性。
| Indicator | Colour in acid | Colour in alkali |
| Litmus | 石蕊 | Red | 红色 | Blue | 蓝色 |
| Methyl orange | 甲基橙 | Red | 红色 | Yellow | 黄色 |
| Thymolphthalein | 百里酚酞 | Colourless | 无色 | Blue | 蓝色 |
| Universal indicator | 通用指示剂 | Red/orange/yellow | 红/橙/黄 | Blue/violet | 蓝/紫 |
3. Reactions of Acids with Metals | 酸与金属的反应
Dilute acids react with many metals to produce a salt and hydrogen gas. The general word equation is:
稀酸与许多金属反应生成盐和氢气。一般文字方程式为：
acid + metal → salt + hydrogen
酸 + 金属 → 盐 + 氢气
For example magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen:
例如镁与盐酸反应生成氯化镁和氢气：
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
Zinc reacts with sulfuric acid to form zinc sulfate and hydrogen:
锌与硫酸反应生成硫酸锌和氢气：
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Only metals above hydrogen in the reactivity series react with dilute acids. Copper, silver and gold do not react with dilute hydrochloric acid.
只有在金属活动性顺序中位于氢之前的金属才能与稀酸反应。铜、银和金不与稀盐酸反应。
The hydrogen gas can be tested using a lighted splint. If hydrogen is present, the splint produces a squeaky pop sound.
氢气可以用点燃的木条检验。如果存在氢气，木条会发出 "squeaky pop" 的爆鸣声。
4. Reactions of Acids with Bases and Alkalis | 酸与碱和碱溶液的反应
Acids react with bases to form a salt and water. This is called neutralisation. The general equation is:
酸与碱反应生成盐和水，这称为中和反应。一般方程式为：
acid + base → salt + water
酸 + 碱 → 盐 + 水
If the base is soluble, it is called an alkali. The ionic equation for neutralisation between H⁺ and OH⁻ ions is:
如果碱可溶于水，则称为碱溶液。H⁺ 和 OH⁻ 离子发生中和反应的离子方程式为：
H⁺(aq) + OH⁻(aq) → H₂O(l)
For example sodium hydroxide neutralises hydrochloric acid to produce sodium chloride and water:
例如氢氧化钠中和盐酸生成氯化钠和水：
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
Many metal oxides and hydroxides are bases. Copper(II) oxide is an insoluble base and reacts with warm sulfuric acid to form copper(II) sulfate solution and water.
许多金属氧化物和氢氧化物都是碱。氧化铜是一种不溶性碱，与温热的硫酸反应生成硫酸铜溶液和水。
Neutralisation is useful in agriculture, for example adding lime to acidic soil to raise its pH. It is also used in indigestion tablets to neutralise excess stomach acid.
中和反应在农业中很有用，例如向酸性土壤中加入石灰以提高 pH。它还可用于抗酸片中和胃里过多的胃酸。
5. Reactions of Acids with Carbonates | 酸与碳酸盐的反应
Dilute acids react with carbonates and hydrogencarbonates to produce a salt, water and carbon dioxide gas. The general pattern is:
稀酸与碳酸盐和碳酸氢盐反应生成盐、水和二氧化碳气体。一般模式为：
acid + carbonate → salt + water + carbon dioxide
酸 + 碳酸盐 → 盐 + 水 + 二氧化碳
For example calcium carbonate reacts with hydrochloric acid:
例如碳酸钙与盐酸反应：
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Another example is sodium carbonate with nitric acid:
另一个例子是碳酸钠与硝酸反应：
Na₂CO₃(s) + 2HNO₃(aq) → 2NaNO₃(aq) + H₂O(l) + CO₂(g)
Carbon dioxide gas is tested by bubbling it through limewater. If carbon dioxide is present, the limewater turns milky or cloudy because insoluble calcium carbonate is formed.
二氧化碳气体可以通过将其通入石灰水中检验。如果存在二氧化碳，石灰水会变浑浊，因为生成了不溶性的碳酸钙。
This reaction explains why acids fizz when added to limestone, marble or eggshells, since these materials contain calcium carbonate.
这个反应解释了为什么酸加到石灰石、大理石或蛋壳中会冒泡，因为这些材料中含有碳酸钙。
6. Making Soluble Salts | 可溶性盐的制备
To make a soluble salt you must first decide whether the reactants are soluble. The method depends on the starting materials.
要制备可溶性盐，首先要判断反应物是否可溶。方法取决于起始原料。
Method 1: add an excess of an insoluble base, metal or carbonate to a fixed volume of dilute acid. Heat gently to speed up the reaction, filter off the excess solid, and then evaporate some of the water to crystallise the salt.
方法一：将过量的不溶性碱、金属或碳酸盐加入一定体积的稀酸中。温和加热以加快反应，过滤掉过量固体，然后蒸发部分水分使盐结晶。
This method works well for salts such as copper(II) sulfate, magnesium sulfate and zinc chloride. The excess solid ensures all the acid is used up.
此方法适用于硫酸铜、硫酸镁和氯化锌等盐。过量的固体可确保酸被完全反应。
Example preparation of copper(II) sulfate crystals:
制备硫酸铜晶体的示例：
CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
Add black copper(II) oxide powder to warm dilute sulfuric acid until no more reacts, filter to remove the excess black solid, then heat the blue filtrate until crystallisation begins.
向温热的稀硫酸中加入黑色氧化铜粉末，直到不再反应为止，过滤除去过量的黑色固体，然后加热蓝色滤液直到开始结晶。
7. Making Soluble Salts by Titration | 用滴定法制备可溶性盐
When both the acid and the base are soluble, you cannot use an excess of solid because both reactants dissolve. Titration is used to find the exact volume of acid needed to neutralise a known volume of alkali.
当酸和碱都可溶时，不能使用过量固体，因为两种反应物都会溶解。滴定法用于确定中和一定体积碱所需的酸的精确体积。
A pipette is used to measure a fixed volume of alkali into a conical flask. A few drops of indicator are added. Acid is run from a burette into the flask until the indicator changes colour. The volume of acid used is recorded.
用移液管量取一定体积的碱溶液到锥形瓶中，加入几滴指示剂。从滴定管中将酸滴入锥形瓶，直到指示剂变色，记录所用酸的体积。
To make a pure salt, repeat the titration without the indicator. Mix the exact volumes of acid and alkali, then evaporate the solution to obtain the salt crystals.
要制备纯盐，重复滴定但不加指示剂。将精确体积的酸和碱混合，然后蒸发溶液得到盐晶体。
Titration is particularly useful for making sodium chloride, potassium nitrate and ammonium salts, where both reactants are soluble.
滴定法特别适用于制备氯化钠、硝酸钾和铵盐，因为这些盐的两种反应物都是可溶的。
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
You may also carry out titration calculations using concentration and volume:
你还可以使用浓度和体积进行滴定计算：
moles = concentration × volume in dm³
物质的量 = 浓度 × 体积（dm³）
8. Making Insoluble Salts by Precipitation | 用沉淀法制备不溶性盐
An insoluble salt can be made by mixing two soluble salt solutions that contain the required ions. The two salts react by double displacement, and the insoluble salt appears as a precipitate.
不溶性盐可以通过混合两种含有所需离子的可溶性盐溶液来制备。两种盐发生复分解反应，不溶性盐以沉淀形式出现。
The precipitate is then filtered, washed with distilled water and left to dry. This method is fast and does not require evaporation.
然后过滤沉淀，用蒸馏水洗涤并晾干。该方法快速，不需要蒸发。
For example silver chloride is made by mixing silver nitrate solution and sodium chloride solution:
例如氯化银通过混合硝酸银溶液和氯化钠溶液制备：
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
Barium sulfate is also prepared this way using barium chloride and dilute sulfuric acid:
硫酸钡也可用该方法通过氯化钡和稀硫酸制备：
BaCl₂(aq) + H₂SO₄(aq) → BaSO₄(s) + 2HCl(aq)
The precipitate colours can be useful for identifying ions: silver chloride is white, silver bromide is cream, silver iodide is yellow, and barium sulfate is white.
沉淀的颜色可用于鉴别离子：氯化银为白色，溴化银为奶油色，碘化银为黄色，硫酸钡为白色。
9. Tests for Gases | 气体的检验
IGCSE exam questions often ask you to identify a gas from its test and positive result. Learn the following table carefully.
IGCSE 考试题目常要求根据检验方法和阳性结果判断气体。请认真学习下表。
| Gas | 气体 | Test | 检验方法 | Positive result | 阳性结果 |
| Hydrogen | 氢气 | Lighted splint | 点燃木条 | Squeaky pop | 爆鸣声 |
| Oxygen | 氧气 | Glowing splint | 带火星木条 | Relights | 复燃 |
| Carbon dioxide | 二氧化碳 | Bubble through limewater | 通入石灰水 | Limewater turns milky | 石灰水变浑浊 |
| Chlorine | 氯气 | Damp litmus paper | 湿润石蕊试纸 | Bleaches white | 漂白变白 |
| Ammonia | 氨气 | Damp red litmus paper | 湿润红色石蕊试纸 | Turns blue | 变蓝 |
For example if a gas relights a glowing splint, it is oxygen. If a gas turns limewater milky, it is carbon dioxide.
例如如果气体使带火星的木条复燃，则它是氧气。如果气体使石灰水变浑浊，则它是二氧化碳。
10. Strong and Weak Acids and Bases | 强酸弱酸与强碱弱碱
A strong acid completely ionises in water, so all its molecules release H⁺ ions. Hydrochloric acid, sulfuric acid and nitric acid are strong acids.
强酸在水中完全电离，因此其所有分子都释放 H⁺ 离子。盐酸、硫酸和硝酸都是强酸。
A weak acid only partially ionises in water, so only some molecules release H⁺ ions. Ethanoic acid is a common weak acid and is written as CH₃COOH.
弱酸在水中只部分电离，因此只有部分分子释放 H⁺ 离子。乙酸是一种常见的弱
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