Acids, Bases and Salts | 酸、碱和盐

📚 Acids, Bases and Salts | 酸、碱和盐

Acids and bases are essential chemical substances that interact to form salts and water. In this revision guide, we explore their definitions, properties, pH measurements, and common reactions required for the Edexcel IGCSE Science syllabus.

酸和碱是相互作用生成盐和水的基础化学物质。在本复习指南中，我们将深入讨论它们的定义、性质、pH值测定以及爱德思IGCSE科学大纲所要求的常见反应。

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 ionises to form H⁺ and Cl⁻ ions.

酸是一种溶于水时产生氢离子（H⁺）的物质。例如，盐酸电离生成H⁺和Cl⁻离子。

A base is a substance that neutralises an acid, often by accepting protons. A soluble base is called an alkali and produces hydroxide ions (OH⁻) when dissolved in water.

碱是一种通过接受质子来中和酸的物质。可溶性碱称为碱液，溶于水时产生氢氧根离子（OH⁻）。

HCl(aq) → H⁺(aq) + Cl⁻(aq)
NaOH(aq) → Na⁺(aq) + OH⁻(aq)

2. Strong and Weak Acids | 强酸与弱酸

Strong acids, such as hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃), ionise completely in water. This means every acid molecule releases a hydrogen ion.

强酸如盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）在水中完全电离，也就是说每个酸分子都会释放一个氢离子。

Weak acids, such as ethanoic acid (CH₃COOH) and carbonic acid (H₂CO₃), ionise only partially. Most of the acid molecules remain unchanged in solution, so the concentration of H⁺ ions is lower.

弱酸如乙酸（CH₃COOH）和碳酸（H₂CO₃）仅部分电离。大多数酸分子在溶液中保持不变，因此H⁺离子浓度较低。

The strength of an acid is different from its concentration. Concentration refers to the amount of acid dissolved in a given volume of water, while strength refers to the degree of ionisation.

酸的强度不同于浓度。浓度指单位体积水中溶解的酸量，而强度指电离的程度。

3. The pH Scale | pH标度

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 pH above 7 is alkaline.

pH标度范围为0到14，用于测量溶液的酸碱度。pH小于7为酸性，pH等于7为中性，pH大于7为碱性。

Universal indicator is a mixture of dyes that changes colour across the whole pH range. It can be used with a colour chart to determine the exact pH.

通用指示剂是多种染料的混合物，能在整个pH范围内变色。它与比色卡配合可测出精确pH值。

In aqueous solution, the pH is related to the concentration of H⁺ ions: the higher the H⁺ concentration, the lower the pH.

在水溶液中，pH与H⁺离子浓度相关：H⁺浓度越高，pH越低。

pH = -log[H⁺]

4. Neutralisation and Salt Formation | 中和反应与盐的生成

Neutralisation is the reaction between an acid and a base to form a salt and water. The H⁺ ions from the acid combine with the OH⁻ ions from the alkali to produce water.

中和反应是酸与碱反应生成盐和水的过程。酸中的H⁺离子与碱液中的OH⁻离子结合生成水。

H⁺(aq) + OH⁻(aq) → H₂O(l)

The name of the salt depends on the acid used and the metal in the base. For example, hydrochloric acid produces chlorides, sulfuric acid produces sulfates, and nitric acid produces nitrates.

盐的名称取决于所用酸和碱中的金属。例如，盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐。

If the base is a metal carbonate, the products are a salt, water and carbon dioxide gas.

如果碱是金属碳酸盐，则产物为盐、水和二氧化碳气体。

5. Preparing Soluble Salts | 可溶性盐的制备

Soluble salts can be prepared by reacting an acid with an appropriate metal, insoluble base or carbonate. The method often involves adding the solid reactant until it is in excess, then filtering off the excess solid.

可溶性盐可通过酸与适当金属、不溶性碱或碳酸盐反应来制备。方法通常是将固体反应物加入过量，然后过滤除去多余的固体。

For a soluble salt from an insoluble base, heat the acid gently and add the base until no more reacts. Filter the mixture to remove excess solid, then evaporate the filtrate to crystallise the salt.

对于用不溶性碱制备可溶性盐，将酸轻微加热并加入碱直到不再反应。过滤混合物以除去过量固体，然后蒸发滤液使盐结晶。

To prepare a soluble salt from a metal, the metal must be more reactive than hydrogen. Copper, for example, does not react with dilute acids, so copper sulfate is usually made using copper oxide.

用金属制备可溶性盐时，金属必须比氢活泼。例如，铜不与稀酸反应，因此硫酸铜通常用氧化铜制备。

6. Preparing Insoluble Salts by Precipitation | 通过沉淀法制备不溶性盐

Some salts are insoluble in water and can be prepared by precipitation. Two soluble reactants are mixed together, and the insoluble salt forms as a solid precipitate.

某些盐不溶于水，可通过沉淀反应制备。将两种可溶性反应物混合，不溶性盐以固体沉淀的形式析出。

For example, silver nitrate and sodium chloride react to form silver chloride and sodium nitrate. The silver chloride is filtered, washed and dried.

例如，硝酸银与氯化钠反应生成氯化银和硝酸钠。过滤、洗涤并干燥氯化银。

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Insoluble salts commonly prepared in the laboratory include barium sulfate (BaSO₄) and lead iodide (PbI₂).

实验室中常见制备的不溶性盐包括硫酸钡（BaSO₄）和碘化铅（PbI₂）。

7. Indicators and Their Colour Changes | 指示剂及其颜色变化

Indicators are dyes that change colour depending on the pH of the solution. Litmus, phenolphthalein and methyl orange are common examples.

指示剂是根据溶液pH变色的染料。常见的有石蕊、酚酞和甲基橙。

Litmus is red in acidic solution and blue in alkaline solution. It is useful for testing whether a solution is acidic or alkaline, but it does not give a pH value.

石蕊在酸性溶液中呈红色，在碱性溶液中呈蓝色。它适用于测试溶液的酸碱性，但不能给出pH值。

Phenolphthalein is colourless in acidic solution and pink in alkaline solution. Methyl orange is red in acidic solution and yellow in alkaline solution.

酚酞在酸性溶液中无色，在碱性溶液中呈粉红色。甲基橙在酸性溶液中呈红色，在碱性溶液中呈黄色。

Indicator	Colour in acid	Colour in alkali
Litmus	Red	Blue
Phenolphthalein	Colourless	Pink
Methyl orange	Red	Yellow

8. Common Reactions of Acids | 酸的常见反应

Acids react with metals, metal oxides, metal hydroxides and metal carbonates. Each reaction produces a salt, often with a gas.

酸与金属、金属氧化物、金属氢氧化物和金属碳酸盐反应。每个反应通常生成盐和气体。

Acid + metal → salt + hydrogen gas. For example, zinc and dilute sulfuric acid produce zinc sulfate and hydrogen.

酸+金属→盐+氢气。例如，锌与稀硫酸反应生成硫酸锌和氢气。

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Acid + carbonate → salt + water + carbon dioxide. This reaction is easily identified by the fizzing of carbon dioxide.

酸+碳酸盐→盐+水+二氧化碳。该反应通过产生二氧化碳气泡来识别。

Metal oxides and metal hydroxides act as bases. They neutralise acids to form a salt and water only, with no gas evolved.

金属氧化物和金属氢氧化物作为碱。它们中和酸只生成盐和水，没有气体产生。

9. Uses of Acids and Bases | 酸和碱的用途

Acids and bases have many important applications in industry, agriculture and everyday life. Sulfuric acid is used in the manufacture of fertilisers, paints and detergents.

酸和碱在工业、农业和日常生活中有着重要应用。硫酸用于制造化肥、油漆和洗涤剂。

Hydrochloric acid is used to clean metals before soldering and to remove rust. Carbonic acid is found in fizzy drinks, giving them their sharp taste.

盐酸用于焊接前清洁金属和除锈。碳酸存在于汽水中，赋予其刺激口感。

Bases such as sodium hydroxide are used to make soap and paper. Magnesium hydroxide is used as an antacid to neutralise excess stomach acid, relieving heartburn.

氢氧化钠等碱用于制造肥皂和纸张。氢氧化镁用作抗酸剂，中和胃中过多的酸，缓解胃灼热。

Calcium hydroxide is used in agriculture to neutralise acidic soils, improving crop growth.

氢氧化钙用于农业中和酸性土壤，改善作物生长。

10. pH and Quantitative Relationships | pH与定量关系

In titration experiments, the exact volume of acid needed to neutralise a known volume of alkali is measured. This allows the concentration of an acid or alkali to be calculated.

在滴定实验中，测量中和已知体积碱液所需酸的准确体积。这可以用于计算酸或碱的浓度。

When an acid and alkali react exactly, the number of moles of H⁺ ions equals the number of moles of OH⁻ ions. The relationship can be expressed as:

当酸与碱恰好完全反应时，H⁺离子的摩尔数等于OH⁻离子的摩尔数。该关系可表示为：

c₁V₁ = c₂V₂

Here c₁ and V₁ are the concentration and volume of the acid, and c₂ and V₂ are those of the alkali, for monoprotic acid and base reactions.

其中c₁和V₁是酸的浓度和体积，c₂和V₂是碱的浓度和体积（适用于一元酸和一元碱反应）。

For acids with two or three hydrogen atoms, such as H₂SO₄, the mole ratio must be considered carefully. One mole of H₂SO₄ produces two moles of H⁺ ions.

对于含有两个或三个氢原子的酸，如H₂SO₄，必须仔细考虑摩尔比。1摩尔H₂SO₄产生2摩尔H⁺离子。

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Acids, Bases and Salts | 酸、碱和盐