Acids, Bases and Salts | 酸、碱和盐

📚 Acids, Bases and Salts | 酸、碱和盐

In this revision guide, you will learn the key ideas about acids, bases and salts that Edexcel IGCSE Science candidates are expected to know. The topic brings together definitions, chemical reactions, laboratory skills and everyday applications.

在本次复习指南中，你将学习Edexcel IGCSE科学考生需要掌握的关于酸碱盐的核心概念。本主题将定义、化学反应、实验技能和日常应用结合在一起。

1. Definitions of Acids and Bases | 酸和碱的定义

An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. For example, hydrochloric acid releases H⁺ ions in aqueous solution.

酸是溶解在水中时产生氢离子（H⁺）的物质。例如，盐酸在水溶液中释放出H⁺离子。

HCl(aq) → H⁺(aq) + Cl⁻(aq)

A base is a substance that neutralises an acid to form water and a salt. An alkali is a soluble base that releases hydroxide ions (OH⁻) in water, such as sodium hydroxide.

碱是一种能中和酸生成水和盐的物质。可溶性碱称为碱液，它在水中释放氢氧根离子（OH⁻），例如氢氧化钠。

• Acids contain hydrogen, but they only show acidic properties when in water.

  酸含有氢，但只有在水溶液中才表现出酸性。

• Common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

  常见酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。

• Common alkalis include sodium hydroxide (NaOH), potassium hydroxide (KOH) and ammonia solution (NH₃(aq)).

  常见碱液包括氢氧化钠（NaOH）、氢氧化钾（KOH）和氨水（NH₃(aq)）。

2. Strong and Weak Acids | 强酸与弱酸

A strong acid is fully ionised in water, meaning every acid particle splits to give H⁺ ions. A weak acid is only partially ionised, so most acid particles remain unchanged.

强酸在水中完全电离，即每个酸分子都产生H⁺离子。弱酸仅部分电离，因此大多数酸分子保持未电离状态。

This difference affects pH, electrical conductivity and reaction rate. A 0.1 mol/dm³ solution of hydrochloric acid has a lower pH than a 0.1 mol/dm³ solution of ethanoic acid, even though their concentrations are the same.

这种差异影响pH值、导电性和反应速率。0.1 mol/dm³盐酸溶液的pH值低于0.1 mol/dm³乙酸溶液，尽管两者浓度相同。

• Strong acids: HCl, H₂SO₄, HNO₃.

  强酸：HCl、H₂SO₄、HNO₃。

• Weak acids: ethanoic acid (CH₃COOH), carbonic acid (H₂CO₃).

  弱酸：乙酸（CH₃COOH）、碳酸（H₂CO₃）。

• Strong alkalis: NaOH, KOH. Weak alkalis: ammonia solution.

  强碱液：NaOH、KOH。弱碱液：氨水。

3. Properties of Acids | 酸的性质

Acids have characteristic properties that are used in identification and reactions.

酸具有可用于鉴别和反应的特征性质。

• Acids turn blue litmus paper red.

  酸使蓝色石蕊试纸变红。

• Acids have a pH lower than 7.

  酸的pH值低于7。

• Acids react with reactive metals to produce a salt and hydrogen gas.

  酸与活泼金属反应生成盐和氢气。

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Hydrogen gas can be tested by the lighted splint: it gives a squeaky pop.

氢气可用点燃的木条检验：会产生“噗”的爆鸣声。

• Acids react with carbonates to produce a salt, water and carbon dioxide.

  酸与碳酸盐反应生成盐、水和二氧化碳。

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

Carbon dioxide turns limewater milky.

二氧化碳使石灰水变浑浊。

4. Properties of Bases and Alkalis | 碱和碱液的性质

Bases include insoluble metal oxides and hydroxides, such as copper(II) oxide. Alkalis are bases that dissolve in water to release OH⁻ ions.

碱包括不溶性金属氧化物和氢氧化物，例如氧化铜。碱液是能在水中溶解并释放OH⁻离子的碱。

• Bases neutralise acids to form a salt and water.

  碱与酸中和生成盐和水。

• Alkalis turn red litmus paper blue.

  碱液使红色石蕊试纸变蓝。

• Alkalis have a pH higher than 7.

  碱液的pH值高于7。

• Alkalis react with ammonium salts to produce a salt, water and ammonia gas.

  碱液与铵盐反应生成盐、水和氨气。

NH₄Cl(aq) + NaOH(aq) → NaCl(aq) +

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