Acids, Bases and Salts for IGCSE Science | IGCSE科学中的酸、碱和盐

📚 Acids, Bases and Salts for IGCSE Science | IGCSE科学中的酸、碱和盐

Acids, bases and salts form a core topic in IGCSE Chemistry, linking everyday substances with laboratory techniques. This guide gives you the essential definitions, reactions, pH theory and salt-preparation methods needed for the Edexcel IGCSE Science (Double Award) specification.

酸碱盐是IGCSE化学中的核心主题，将日常物质与实验技能连结起来。本指南为你提供Edexcel IGCSE科学（双奖）大纲所需的关键定义、反应、pH理论和盐的制备方法。

1. What Are Acids and Bases? | 什么是酸和碱？

An acid is a substance that dissolves in water to produce hydrogen ions, H⁺. For example, hydrochloric acid gives H⁺ and Cl⁻ ions.

酸是一种溶于水后产生氢离子（H⁺）的物质。例如，盐酸在水中解离产生H⁺和Cl⁻离子。

HCl → H⁺ + Cl⁻

A base is a substance that neutralises an acid. Bases include metal oxides, metal hydroxides and metal carbonates. An alkali is a soluble base that dissolves in water to produce hydroxide ions, OH⁻.

碱是能中和酸的物质。碱包括金属氧化物、金属氢氧化物和金属碳酸盐。可溶性碱是溶于水后产生氢氧根离子（OH⁻）的碱。

Common acids: sulfuric acid (H₂SO₄), hydrochloric acid (HCl), nitric acid (HNO₃), ethanoic acid (CH₃COOH).

常见酸：硫酸H₂SO₄、盐酸HCl、硝酸HNO₃、乙酸CH₃COOH。
Common alkalis: sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), aqueous ammonia (NH₃).

常见可溶性碱：氢氧化钠NaOH、氢氧化钾KOH、氢氧化钙Ca(OH)₂、氨水NH₃。

2. The pH Scale and Indicators | pH标度和指示剂

The pH scale runs from 0 to 14 and tells us how acidic or alkaline a solution is. An acid has pH less than 7, a neutral solution has pH exactly 7, and an alkali has pH greater than 7.

pH标度范围是0到14，用于表示溶液的酸碱性。酸性溶液的pH小于7，中性溶液pH等于7，碱性溶液pH大于7。

pH 0–2: strong acid, e.g. concentrated hydrochloric acid.

pH 0–2：强酸，如浓盐酸。
pH 6–7: weak acid or neutral, e.g. milk or distilled water.

pH 6–7：弱酸或中性，如牛奶或蒸馏水。
pH 13–14: strong alkali, e.g. sodium hydroxide solution.

pH 13–14：强碱，如氢氧化钠溶液。

Universal indicator gives a continuous range of colours: red for strong acid, orange/yellow for weak acid, green for neutral, blue for weak alkali and purple for strong alkali. Litmus is simpler: red in acid, blue in alkali.

万能指示剂呈现连续的颜色变化：强酸红色，弱酸橙黄，中性绿色，弱碱蓝色，强碱紫色。石蕊更简单：遇酸变红，遇碱变蓝。

3. Properties of Acids | 酸的性质

Acids have several characteristic properties that can be tested in the laboratory. It is important to know both the observation and the word/symbol equation for each reaction.

酸有一些可以通过实验检验的特征性质。重要的是要同时掌握实验现象以及对应的文字方程式或符号方程式。

Acid + metal → salt + hydrogen. Example: Mg + 2HCl → MgCl₂ + H₂. The hydrogen is confirmed by a lighted splint giving a ‘squeaky pop’.

酸 + 金属 → 盐 + 氢气。例如：Mg + 2HCl → MgCl₂ + H₂。氢气用燃着的木条检验，会发出“噗”的爆鸣声。
Acid + carbonate → salt + water + carbon dioxide. Example: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Carbon dioxide turns limewater milky.

酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。例如：CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂。二氧化碳使石灰水变浑浊。
Acid + base → salt + water. This is neutralisation, covered in detail later.

酸 + 碱 → 盐 + 水。这就是中和反应，后面会详细介绍。

zinc + sulfuric acid → zinc sulfate + hydrogen
Zn + H₂SO₄ → ZnSO₄ + H₂

4. Properties of Bases and Alkalis | 碱和可溶性碱的性质

Bases often feel soapy and taste bitter, but you should never taste laboratory chemicals. Insoluble bases react with acids only when they are added in excess; any unreacted solid can be filtered off.

碱通常有滑腻感和苦味，但绝不可以尝实验室化学品。不溶性碱与酸反应时，需加入过量固体；未反应完的固体可以过滤除去。

Alkalis turn red litmus blue and universal indicator blue/purple.

可溶性碱使红色石蕊变蓝，使万能指示剂变蓝或紫。
Alkalis react with ammonium salts to release ammonia gas, which has a pungent smell and turns damp red litmus blue.

可溶性碱与铵盐反应释放氨气。氨气有刺激性气味，能使湿润的红色石蕊试纸变蓝。
Base + acid → salt + water. Example: CuO + H₂SO₄ → CuSO₄ + H₂O. The black copper(II) oxide dissolves to form a blue solution.

碱 + 酸 → 盐 + 水。例如：CuO + H₂SO₄ → CuSO₄ + H₂O。黑色氧化铜溶解，生成蓝色溶液。

5. Strength vs Concentration | 强度与浓度

A common exam trap is confusing strength with concentration. Strength depends on how well the acid ionises in water. Concentration depends on how much acid is dissolved in a given volume of solution.

一个常见的考试陷阱是混淆“强度”和“浓度”。强度取决于酸在水中的电离程度，而浓度取决于单位体积溶液中所含酸的量。

A strong acid fully ionises in water. Example: HCl → H⁺ + Cl⁻ (complete).

强酸在水中完全电离。例如：HCl → H⁺ + Cl⁻（完全）。
A weak acid partially ionises. Example: CH₃COOH ⇌ CH₃COO⁻ + H⁺ (reversible).

弱酸部分电离。例如：CH₃COOH ⇌ CH₃COO⁻ + H⁺（可逆）。
At the same concentration, a strong acid has a lower pH than a weak acid because it produces more H⁺ ions.

在相同浓度下，强酸的pH比弱酸低，因为它产生更多H⁺离子。

Increasing concentration of an acid decreases pH (makes it more acidic)
增加酸浓度会降低pH（酸性更强）

6. Neutralisation Reactions | 中和反应

Neutralisation is the reaction between an acid and a base to form a salt and water only. The ionic equation is:

中和反应是酸与碱反应只生成盐和水的过程。其离子方程式为：

H⁺(aq) + OH⁻(aq) → H₂O(l)

For example, sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water:

例如，氢氧化钠与盐酸反应生成氯化钠和水：

NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

In the exam you should remember the names of the salts produced:

考试中需要记住生成盐的名称：

Hydrochloric acid → chloride salts, e.g. potassium chloride, zinc chloride.

盐酸 → 氯化物盐，如氯化钾、氯化锌。
Sulfuric acid → sulfate salts, e.g. copper sulfate, ammonium sulfate.

硫酸 → 硫酸盐，如硫酸铜、硫酸铵。
Nitric acid → nitrate salts, e.g. silver nitrate, sodium nitrate.

硝酸 → 硝酸盐，如硝酸银、硝酸钠。

7. Making Soluble Salts | 制取可溶性盐

Soluble salts can be made by reacting an acid with an insoluble base or carbonate, or with a suitable metal. The key is to add the solid in excess so that all the acid is used up.

可溶性盐可以通过酸与不溶性碱、碳酸盐或合适的金属反应来制取。关键是把固体加入过量，确保所有酸完全反应。

General method for acid + insoluble base/carbonate:

酸 + 不溶性碱/碳酸盐的一般步骤：

Warm a measured volume of dilute acid in a beaker.

在烧杯中加热量取好的稀酸。
Add excess insoluble solid (e.g. copper(II) oxide or calcium carbonate) and stir until no more dissolves.

加入过量的不溶性固体（如氧化铜或碳酸钙），搅拌直到不再溶解。
Filter the mixture to remove excess solid; the filtrate is the salt solution.

过滤混合物以除去过量的固体；滤液就是盐溶液。
Evaporate some water, then leave to crystallise.

蒸发部分水分，然后静置结晶。

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

8. Titration Procedure | 滴定法

Titration is used when both the acid and alkali are soluble, so you cannot simply filter off excess solid. It allows you to find the exact volume of acid needed to neutralise a known volume of alkali.

当酸和碱都可溶时，不能靠过滤除去过量固体，此时使用滴定法。滴定可以准确找到中和已知体积碱所需酸的体积。

Steps for titration:

滴定步骤：

Use a pipette to measure a fixed volume of alkali into a conical flask, and add a few drops of indicator.

用移液管量取固定体积的碱放入锥形瓶，并滴加几滴指示剂。
Fill a burette with the acid and record the initial reading.

用酸装满滴定管，记录初始读数。
Add acid slowly while swirling the flask until the indicator just changes colour (end point).

边振荡锥形瓶边缓慢加入酸，直到指示剂刚好变色（终点）。
Record the final reading and repeat without indicator to obtain a pure salt solution, which can be crystallised.

记录最终读数，然后不加指示剂重复实验以获得纯净盐溶液，再进行结晶。

Example reaction:

示例反应：

H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l)

9. Making Insoluble Salts by Precipitation | 沉淀法制取不溶性盐

Some salts are insoluble in water, for example silver chloride and lead(II) iodide. These are made by mixing solutions of two soluble salts so that an insoluble salt precipitates out.

有些盐不溶于水，例如氯化银和碘化铅。这些盐可以通过混合两种可溶盐溶液，使不溶盐沉淀出来。

Example for lead(II) iodide:

碘化铅的制备示例：

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

The ionic equation ignores the spectator ions K⁺ and NO₃⁻:

离子方程式忽略旁观离子K⁺和NO₃⁻：

Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s)

Filter the mixture to collect the precipitate.

过滤混合物以收集沉淀。
Wash the residue with distilled water and dry it in a warm oven.

用蒸馏水洗涤滤渣，并在温暖烘箱中干燥。

10. Applications of Neutralisation | 中和反应的应用

Neutralisation is used in everyday life and agriculture:

中和反应广泛应用于日常生活和农业中：

Antacids contain weak bases such as magnesium hydroxide or calcium carbonate to reduce excess stomach acid.

抗酸药含有弱碱，如氢氧化镁或碳酸钙，用于减少胃酸过多。
Farmers add calcium oxide (lime) or calcium hydroxide to neutralise acidic soil.

农民通过添加氧化钙（生石灰）或氢氧化钙来中和酸性土壤。
Bee stings are acidic (formic acid) and can be treated with baking soda; wasp stings are alkaline and can be treated with vinegar.

蜜蜂蜇伤属酸性（甲酸），可用小苏打处理；黄蜂蜇伤属碱性，可用醋处理。

11. Common Exam Pitfalls | 常见考试误区

Avoiding these common mistakes can save valuable marks:

避免这些常见错误可以帮你保住宝贵的分数：

Writing state symbols: always include (aq), (s), (l), (g) where appropriate, especially in ionic equations.

书写状态符号：在合适的时候务必写(aq)、(s)、(l)、(g)，尤其是在离子方程式中。
Confusing proton H⁺ with hydrogen molecule H₂ or hydrogen atom H.

混淆质子H⁺、氢分子H₂和氢原子H。
Forgetting that an acid reacting with a metal carbonate produces carbon dioxide and water, not hydrogen.

忘记酸与金属碳酸盐反应生成的是二氧化碳和水，而不是氢气。
Using the wrong salt name: sulfuric acid makes sulfates, nitric acid makes nitrates, hydrochloric acid makes chlorides.

写出错误的盐名：硫酸生成硫酸盐，硝酸生成硝酸盐，盐酸生成氯化物。
Saying ‘the acid is strong’ when you mean ‘the acid is concentrated’ — strengthen and concentration are different ideas.

把“浓缩”说成“强”——强度和浓度是两个不同的概念。

Master these ideas, practise writing equations, and you will be well prepared for the acid–base and salt questions in your IGCSE Science exam.

掌握这些概念，勤加练习书写方程式，你就能为IGCSE科学考试中的酸碱盐问题做好准备。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Acids, Bases and Salts for IGCSE Science | IGCSE科学中的酸、碱和盐