📚 Making Salts | 盐的制备
Making salts is a core practical topic in KS3 chemistry. It shows how acids react with metals, metal oxides, metal hydroxides and carbonates to form useful compounds called salts. Understanding these reactions helps you predict products, name salts correctly and carry out a safe preparation in the laboratory.
盐的制备是 KS3 化学中一个核心实验主题。它展示了酸如何与金属、金属氧化物、金属氢氧化物和碳酸盐反应，生成被称为盐的有用化合物。理解这些反应有助于你预测产物、正确命名盐，并在实验室中安全地完成制备。
1. What is a Salt? | 什么是盐？
In chemistry, a salt is a compound formed when the hydrogen ion in an acid is replaced by a metal ion or an ammonium ion. Salts are usually ionic solids, and many are soluble in water. A familiar example is sodium chloride, NaCl, which is common table salt.
在化学中，盐是酸中的氢离子被金属离子或铵根离子取代后形成的化合物。盐通常是离子固体，许多盐可溶于水。一个熟悉的例子是氯化钠 NaCl，也就是普通的食盐。
A salt is made of a positive ion from a base or metal, and a negative ion from an acid. For example, copper sulfate contains copper ions, Cu²⁺, and sulfate ions, SO₄²⁻. The ions are held together by strong ionic bonds in a regular lattice.
盐由来自碱或金属的正离子和来自酸的负离子组成。例如，硫酸铜含有铜离子 Cu²⁺ 和硫酸根离子 SO₄²⁻。这些离子通过强离子键在规则晶格中结合在一起。
2. Naming Salts | 盐的命名
The name of a salt has two parts. The first part comes from the metal or base used, and the second part comes from the acid. Once you know the acid, you can work out the salt name.
盐的名称由两部分组成。第一部分来自所用的金属或碱，第二部分来自所用的酸。一旦你知道酸，就可以推断出盐的名称。
- Hydrochloric acid (HCl) produces chloride salts | 盐酸 (HCl) 生成氯化物盐
- Sulfuric acid (H₂SO₄) produces sulfate salts | 硫酸 (H₂SO₄) 生成硫酸盐
- Nitric acid (HNO₃) produces nitrate salts | 硝酸 (HNO₃) 生成硝酸盐
For example, sodium hydroxide reacting with hydrochloric acid produces sodium chloride. Copper oxide reacting with sulfuric acid produces copper sulfate. Calcium carbonate reacting with nitric acid produces calcium nitrate.
例如，氢氧化钠与盐酸反应生成氯化钠。氧化铜与硫酸反应生成硫酸铜。碳酸钙与硝酸反应生成硝酸钙。
3. Neutralisation and Salt Formation | 中和反应与盐的生成
A neutralisation reaction occurs when an acid reacts with a base. The products are always a salt and water. This is one of the most important ways to make a salt in the laboratory.
中和反应发生在酸与碱反应时。产物总是盐和水。这是实验室中制盐最重要的方法之一。
acid + base → salt + water
酸 + 碱 → 盐 + 水
A simple example is the reaction between hydrochloric acid and sodium hydroxide:
一个简单的例子是盐酸与氢氧化钠的反应：
HCl + NaOH → NaCl + H₂O
The pH of the mixture changes during neutralisation. An acidic solution has a low pH, and an alkaline solution has a high pH. When exactly neutralised, the solution has pH 7 and contains the salt dissolved in water.
中和过程中混合物的 pH 会发生变化。酸性溶液 pH 较低，碱性溶液 pH 较高。当恰好完全中和时，溶液的 pH 为 7，其中含有溶解在水中的盐。
4. Making Salts from Metals and Acids | 用金属与酸制盐
Some reactive metals react with dilute acids to produce a salt and hydrogen gas. This method works well with metals such as magnesium, zinc and iron, but it is not suitable for very reactive metals like potassium or sodium because the reaction is too violent.
一些活泼金属能与稀酸反应，生成盐和氢气。这种方法适用于镁、锌和铁等金属，但不适用于钾或钠等非常活泼的金属，因为反应过于剧烈。
metal + acid → salt + hydrogen
金属 + 酸 → 盐 + 氢气
For example, magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas:
例如，镁与盐酸反应生成氯化镁和氢气：
Mg + 2HCl → MgCl₂ + H₂
You can observe bubbles of gas during the reaction. The gas can be tested with a burning splint. If hydrogen is present, it burns with a squeaky pop sound. The metal disappears as it is used up, leaving a solution of the salt.
反应过程中可以观察到气泡。可以用点燃的木条检验该气体。如果存在氢气，它会燃烧并发出咝咝的爆鸣声。金属随着反应进行而消失，留下盐溶液。
5. Making Salts from Metal Oxides and Hydroxides | 用金属氧化物和氢氧化物制盐
Metal oxides and metal hydroxides are bases. They react with acids to form a salt and water only. This makes them useful for preparing salts because no unwanted gas is produced.
金属氧化物和金属氢氧化物都是碱。它们与酸反应只生成盐和水。这使得它们非常适合制备盐，因为不会产生多余的气体。
metal oxide + acid → salt + water
金属氧化物 + 酸 → 盐 + 水
metal hydroxide + acid → salt + water
金属氢氧化物 + 酸 → 盐 + 水
For example, black copper oxide reacts with warm dilute sulfuric acid to form a blue solution of copper sulfate:
例如，黑色的氧化铜与温热的稀硫酸反应，生成蓝色的硫酸铜溶液：
CuO + H₂SO₄ → CuSO₄ + H₂O
This reaction is often used in the laboratory to make copper sulfate crystals. The mixture is warmed gently, and excess copper oxide is added until no more reacts. The unreacted solid is then removed by filtration.
该反应常用于实验室制备硫酸铜晶体。将混合物温和加热，并加入过量的氧化铜直至不再反应。然后通过过滤除去未反应的固体。
6. Making Salts from Carbonates | 用碳酸盐制盐
Metal carbonates react with acids to produce a salt, water and carbon dioxide gas. This reaction is easy to observe because bubbling occurs as carbon dioxide is released.
金属碳酸盐与酸反应生成盐、水和二氧化碳气体。这个反应很容易观察，因为释放二氧化碳时会产生气泡。
metal carbonate + acid → salt + water + carbon dioxide
金属碳酸盐 + 酸 → 盐 + 水 + 二氧化碳
For example, calcium carbonate reacts with hydrochloric acid to form calcium chloride, water and carbon dioxide:
例如，碳酸钙与盐酸反应生成氯化钙、水和二氧化碳：
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Carbon dioxide can be tested by bubbling the gas through limewater. The limewater turns cloudy or milky because calcium carbonate is formed. This is a useful way to confirm that a carbonate has reacted.
可以将气体通入石灰水中检验二氧化碳。石灰水变浑浊或呈乳白色，这是因为生成了碳酸钙。这是确认碳酸盐发生反应的有效方法。
7. Choosing the Right Method | 选择合适的方法
To prepare a soluble salt, chemists often react an acid with an insoluble base such as a metal oxide, metal hydroxide or metal carbonate. The insoluble solid is added in excess, which makes sure all the acid has reacted. The excess solid can then be removed by filtration.
为了制备可溶性盐，化学家通常让酸与不溶性碱（如金属氧化物、金属氢氧化物或金属碳酸盐）反应。将不溶性固体过量加入，确保所有酸都反应完毕。然后可以通过过滤除去过量的固体。
Using a metal and an acid also works, but it can be more hazardous because hydrogen gas is produced. The reaction may also be slow with some metals. In the school laboratory, metal oxides and carbonates are often safer choices for making salts.
使用金属与酸反应也可以，但由于会产生氢气，因此可能更危险。有些金属的反应也可能较慢。在学校实验室中，金属氧化物和碳酸盐通常是更安全的制盐选择。
8. Preparing a Pure Dry Salt | 制备纯净干燥的盐
Follow these steps to make a pure, dry sample of a soluble salt from an insoluble base and an acid. A common example is preparing copper sulfate crystals from copper oxide and sulfuric acid.
按照以下步骤，可以用不溶性碱和酸制备纯净干燥的可溶性盐样品。一个常见的例子是用氧化铜和硫酸制备硫酸铜晶体。
- Measure a fixed volume of dilute acid into a beaker | 用量筒量取一定体积的稀酸倒入烧杯中
- Add the insoluble base a little at a time and stir | 少量多次地加入不溶性碱并搅拌
- Warm the mixture gently to speed up the reaction | 温和加热混合物以加快反应
- Stop adding solid when no more reacts and some solid remains | 当不再反应且仍有固体剩余时停止加入
- Filter the mixture to remove the excess solid | 过滤混合物以除去过量固体
- Pour the filtrate into an evaporating dish and heat to evaporate some water | 将滤液倒入蒸发皿中加热，蒸发部分水分
- Leave the concentrated solution to cool slowly so crystals form | 让浓缩溶液缓慢冷却，使晶体析出
- Dry the crystals between pieces of filter paper | 用滤纸将晶体吸干
The key idea is to add the base in excess. This ensures that all the acid is used up, so the final salt is not contaminated with unreacted acid. The excess base is then removed by filtration.
关键思路是加入过量的碱。这可以确保所有酸都被消耗掉，因此最终盐不会被未反应的酸污染。然后通过过滤除去过量的碱。
9. Common Salts and Their Uses | 常见盐及其用途
Salts are not only laboratory chemicals. Many salts are used in everyday life, in food, medicine, agriculture and building materials. The table below shows some common examples.
盐不仅是实验室化学品。许多盐在日常生活中都有用途，涉及食品、医药、农业和建筑材料。下表列出了一些常见例子。
| Salt | 盐 | Formula | 化学式 | Use | 用途 |
|---|---|---|
| Sodium chloride | 氯化钠 | NaCl | Table salt and food preservative | 食盐和食品防腐剂 |
| Calcium carbonate | 碳酸钙 | CaCO₃ | Chalk, limestone and antacid tablets | 粉笔、石灰石和抗酸药片 |
| Copper sulfate | 硫酸铜 | CuSO₄ | Fungicide and crystal growing | 杀菌剂和晶体培养 |
| Magnesium sulfate | 硫酸镁 | MgSO₄ | Epsom salts for baths | 浴用泻盐 |
| Potassium nitrate | 硝酸钾 | KNO₃ | Fertiliser and food preservative | 肥料和食品防腐剂 |
Being able to link a salt's name to its uses helps you see why salt preparation is an important part of chemistry. The same principles are used in industry to make these compounds on a large scale.
能够将盐的名称与其用途联系起来，有助于你理解为什么盐的制备是化学的重要内容。工业中也运用相同的原理大规模生产这些化合物。
10. Safety in the Lab | 实验室安全
When making salts, you must always follow safety rules. Wear eye protection because acids are corrosive and can damage eyes. Use dilute acids to reduce risk, and add solids slowly to avoid splashing.
制备盐时，必须始终遵守安全规则。佩戴护目镜，因为酸具有腐蚀性，可能损伤眼睛。使用稀酸以降低风险，并缓慢加入固体以避免飞溅。
Do not evaporate a salt solution to complete dryness while heating strongly, because hot solid particles can spit out. Instead, evaporate some water and allow crystallisation to finish slowly. Always follow your teacher's instructions and clean the equipment after use.
不要强热将盐溶液完全蒸干，因为高温固体颗粒可能飞溅。应当蒸发部分水分，然后让结晶缓慢完成。始终遵循老师的指导，并在实验后清洁仪器。
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