Acids, Bases and Salts | 酸、碱与盐

📚 Acids, Bases and Salts | 酸、碱与盐

Acids, bases and salts form one of the most important topics in IGCSE Chemistry. Understanding their properties, reactions and the methods used to prepare salts is essential for exam success.

酸、碱与盐是 IGCSE 化学中最重要的主题之一。理解它们的性质、反应以及制备盐的方法，对考试成功至关重要。

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1. Properties of Acids | 酸的性质

An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. Acids have a sour taste, turn blue litmus paper red, and have a pH less than 7.

酸是一种溶于水时产生氢离子（H⁺）的物质。酸有酸味，能使蓝色石蕊试纸变红，并且 pH 小于 7。

• Acids are corrosive and can damage skin and metals.

  酸具有腐蚀性，会损伤皮肤和金属。

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

  常见例子包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。

• Dilute acids contain H⁺ ions, which are responsible for acidic properties.

  稀酸中含有 H⁺ 离子，这是酸性的来源。

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2. Properties of Bases | 碱的性质

A base is a substance that neutralises an acid to form a salt and water only. Bases that are soluble in water are called alkalis. Alkalis produce hydroxide ions (OH⁻) in aqueous solution.

碱是一种能与酸反应生成盐和水的物质。可溶于水的碱称为碱（alkali）。碱在水溶液中产生氢氧根离子（OH⁻）。

• Bases turn red litmus paper blue and have a pH greater than 7.

  碱能使红色石蕊试纸变蓝，pH 大于 7。

• Examples of bases include copper(II) oxide (CuO) and sodium hydroxide (NaOH).

  碱的例子包括氧化铜（CuO）和氢氧化钠（NaOH）。

• Insoluble bases include most metal oxides and hydroxides.

  不溶性碱包括大多数金属氧化物和氢氧化物。

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3. The pH Scale | pH 标度

The pH scale measures how acidic or alkaline a solution is. It runs from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline.

pH 标度用于衡量溶液的酸碱性。范围从 0 到 14。pH 等于 7 为中性，小于 7 为酸性，大于 7 为碱性。

pH < 7 → acidic | pH = 7 → neutral | pH > 7 → alkaline

• Universal indicator gives a colour change across the pH range.

  万能指示剂在不同 pH 下会呈现不同颜色。

• The lower the pH, the higher the concentration of H⁺ ions.

  pH 越低，H⁺ 离子浓度越高。

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4. Neutralisation | 中和反应

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

中和反应是酸与碱反应生成盐和水的过程。离子方程式为：

H⁺ (aq) + OH⁻ (aq) → H₂O (l)

This reaction is exothermic and always releases heat energy.

该反应是放热反应，总是释放热能。

• Acid + alkali → salt + water

  酸 + 碱 → 盐 + 水

• Acid + metal oxide → salt + water

  酸 + 金属氧化物 → 盐 + 水

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5. Reactions of Acids with Metals | 酸与金属的反应

Acids react with certain metals to produce a salt and hydrogen gas. Only metals above hydrogen in the reactivity series will react.

酸与某些金属反应生成盐和氢气。只有活泼性顺序中排在氢之前的金属才能反应。

Acid + Metal → Salt + Hydrogen

For example, magnesium reacts with dilute hydrochloric acid:

例如，镁与稀盐酸反应：

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

The hydrogen gas can be tested with a lighted splint – it makes a squeaky pop.

氢气可用点燃的火柴检验——会发出“噗”的爆鸣声。

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6. Reactions of Acids with Carbonates | 酸与碳酸盐的反应

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

酸与碳酸盐和碳酸氢盐反应生成盐、水和二氧化碳气体。

Acid + Carbonate → Salt + Water + CO₂

For example, calcium carbonate reacts with nitric acid:

例如，碳酸钙与硝酸反应：

CaCO₃ (s) + 2HNO₃ (aq) → Ca(NO₃)₂ (aq) + H₂O (l) + CO₂ (g)

Carbon dioxide is tested by bubbling it through limewater – it turns milky.

二氧化碳可通过通入石灰水检验——石灰水变浑浊。

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7. Preparation of Salts | 盐的制备

Salts can be prepared by neutralisation, by reacting acids with metals, insoluble bases, or carbonates. The method depends on whether the salt is soluble or insoluble.

盐可以通过中和反应、酸与金属、不溶性碱或碳酸盐反应来制备。方法取决于盐是可溶还是不可溶。

Soluble Salt	Method
Sodium chloride	Titration of NaOH with HCl
Copper(II) sulfate	React CuO with H₂SO₄, then evaporate
Lead(II) chloride	Precipitation from Pb(NO₃)₂ and NaCl

Insoluble salts are made by precipitation. The precipitate is filtered, washed and dried.

不溶性盐通过沉淀反应制备。沉淀经过过滤、洗涤和干燥。

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8. Tests for Gases | 气体检验

Knowing the tests for common gases is essential for identifying reaction products.

掌握常见气体的检验方法对识别反应产物至关重要。

• Hydrogen (H₂): lighted splint → squeaky pop.

  氢气（H₂）： 点燃的木条 → 爆鸣声。

• Carbon dioxide (CO₂): limewater turns milky.

  二氧化碳（CO₂）： 石灰水变浑浊。

• Oxygen (O₂): glowing splint relights.

  氧气（O₂）： 余烬的木条复燃。

• Ammonia (NH₃): damp red litmus paper turns blue.

  氨气（NH₃）： 湿润红色石蕊试纸变蓝。

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9. Solubility Rules | 溶解度规则

Predicting whether a salt is soluble or insoluble is a key skill. The following rules apply to most common salts.

预测盐是否可溶是一项关键技能。以下规则适用于大多数常见盐。

Soluble	Insoluble
All sodium, potassium and ammonium salts	Most silver and lead salts (except nitrate)
All nitrates	Lead(II) chloride, silver chloride
Most chlorides, bromides and iodides	Barium sulfate, calcium sulfate (slightly)
Most sulfates	Most carbonates, hydroxides (except Na⁺, K⁺, NH₄⁺)

These rules help decide the correct method for preparing a salt.

这些规则有助于选择正确的盐制备方法。

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10. Applications in Everyday Life | 在日常生活中的应用

Acids and bases are widely used in industry, agriculture and medicine. For example, sulfuric acid is used in car batteries, and magnesium hydroxide is used as an antacid to relieve indigestion.

酸和碱广泛用于工业、农业和医药。例如，硫酸用于汽车电池，氢氧化镁用作抗酸剂缓解消化不良。

• Lime (calcium oxide) is added to acidic soil to neutralise it.

  石灰（氧化钙）用于中和酸性土壤。

• Citric acid is used in food preservation and flavouring.

  柠檬酸用于食品防腐和调味。

• Ammonia is used to make fertilisers.

  氨用于制造肥料。

Understanding these reactions helps us control chemical processes safely and efficiently.

理解这些反应有助于我们安全高效地控制化学过程。

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