📚 Reaction of Metal Oxides with Acids | 金属氧化物与酸的反应
Metal oxides are compounds formed when metals react with oxygen. Many metal oxides behave as bases, which means they can neutralise acids to form a salt and water. This reaction is a key topic in KS3 Chemistry and appears frequently in CIE-style worksheets and exam questions. Understanding the pattern helps you predict products, name salts correctly and write word equations and balanced symbol equations with confidence.
金属氧化物是金属与氧气反应生成的化合物。许多金属氧化物是碱，也就是说它们能中和酸，生成盐和水。这个反应是 KS3 化学的重要主题，也经常出现在 CIE 风格的练习题和考试题中。理解这一规律有助于你预测产物、正确命名盐，并自信地书写文字方程式和配平的符号方程式。
1. What Are Metal Oxides? | 什么是金属氧化物？
A metal oxide is a compound containing a metal and oxygen. Examples include copper(II) oxide (CuO), magnesium oxide (MgO), iron(III) oxide (Fe₂O₃), zinc oxide (ZnO) and aluminium oxide (Al₂O₃). These compounds are usually solid at room temperature, often as powders, and many are insoluble in water.
金属氧化物是含有金属和氧的化合物。例如氧化铜 (CuO)、氧化镁 (MgO)、氧化铁 (Fe₂O₃)、氧化锌 (ZnO) 和氧化铝 (Al₂O₃)。这些化合物在室温下通常是固体，常为粉末状，其中许多不溶于水。
When a metal can form more than one ion, a Roman numeral in the name shows its oxidation state. For example, iron(II) oxide is FeO, while iron(III) oxide is Fe₂O₃. Copper(I) oxide is Cu₂O, while copper(II) oxide is CuO. This naming detail matters because the formula of the salt produced depends on the metal ion present.
当金属能形成一种以上离子时，名称中的罗马数字表示它的氧化态。例如，氧化亚铁是 FeO，而氧化铁是 Fe₂O₃；氧化亚铜是 Cu₂O，而氧化铜是 CuO。这个命名细节很重要，因为生成盐的化学式取决于存在的金属离子。
o form white magnesium oxide powder. The general word equation for this formation is: metal + oxygen → metal oxide.
金属氧化物可以通过在空气或氧气中燃烧金属来生成，也可以通过加热金属与氧气反应来生成。例如，镁燃烧时发出明亮的白色火焰，生成白色氧化镁粉末。这种生成反应的一般文字方程式是：金属 + 氧气 → 金属氧化物。
2Mg + O₂ → 2MgO
2. Metal Oxides as Bases and Alkalis | 金属氧化物作为碱与可溶性碱
A base is a substance that can react with an acid to form a salt and water. Most metal oxides are bases because they carry out this neutralisation reaction. Bases are the chemical opposite of acids. This is why metal oxides are often described as basic oxides.
碱是能与酸反应生成盐和水的物质。大多数金属氧化物是碱，因为它们可以进行这种中和反应。碱在化学上是酸的对立面。因此，金属氧化物常被称为碱性氧化物。
Some bases, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH), dissolve in water and are called alkalis. However, most metal oxides do not dissolve in water, so they are insoluble bases rather than alkalis. This difference is important when designing experiments to make salts.
一些碱，例如氢氧化钠 (NaOH) 和氢氧化钾 (KOH)，溶于水，称为可溶性碱。但是，大多数金属氧化物不溶于水，因此它们是不溶性碱，而不是可溶性碱。在设计制备盐的实验时，这一区别非常重要。
Because an insoluble metal oxide does not dissolve, it can be added little by little to an acid until no more reacts. The excess solid can then be removed by filtration. This is a standard method for preparing soluble salts from insoluble bases.
由于不溶性金属氧化物不会溶解，可以将其少量多次加入酸中，直到不再反应。过量的固体随后可以通过过滤除去。这是用不溶性碱制备可溶性盐的标准方法。
3. The General Word Equation | 通用文字方程式
The reaction between a metal oxide and an acid always follows the same pattern. In words, the general equation is:
金属氧化物与酸的反应总是遵循相同的模式。用文字表示，通用方程式为：
金属氧化物 + 酸 → 盐 + 水
For example, copper(II) oxide reacts with sulfuric acid to form copper(II) sulfate and water. Magnesium oxide reacts with hydrochloric acid to form magnesium chloride and water. The metal in the oxide becomes the metal ion in the salt, while the oxygen and hydrogen from the acid combine to form water.
例如，氧化铜与硫酸反应生成硫酸铜和水。氧化镁与盐酸反应生成氯化镁和水。氧化物中的金属变成盐中的金属离子，而酸中的氧和氢结合生成水。
The acid used determines the salt produced. Hydrochloric acid produces chlorides, sulfuric acid produces sulfates, nitric acid produces nitrates, and phosphoric acid produces phosphates. Ethanoic acid produces ethanoates. This connection is one of the most frequently tested points in KS3 and CIE chemistry.
所用的酸决定生成的盐。盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐，磷酸生成磷酸盐，乙酸生成乙酸盐。这一联系是 KS3 和 CIE 化学中最常考的知识点之一。
4. Naming the Salt: Linking Acid to Salt | 盐的命名：从酸到盐
To name the salt, first identify the metal ion from the metal oxide, then identify the negative ion from the acid. The table below shows the most common acids and the salts they form.
要命名盐，先确定来自金属氧化物的金属离子，再确定来自酸的酸根离子。下表列出了最常见的酸及其生成的盐。
| Acid | Salt produced | Example |
|---|---|---|
| Hydrochloric acid (HCl) | chloride | copper(II) chloride |
| Sulfuric acid (H₂SO₄) | sulfate | magnesium sulfate |
| Nitric acid (HNO₃) | nitrate | zinc nitrate |
| Phosphoric acid (H₃PO₄) | phosphate | calcium phosphate |
| Ethanoic acid (CH₃COOH) | ethanoate | sodium ethanoate |
If the metal has more than one possible ion, the Roman numeral must be included. For example, iron(II) oxide with hydrochloric acid gives iron(II) chloride, while iron(III) oxide with hydrochloric acid gives iron(III) chloride. Do not confuse the two, because their formulae are different: FeCl₂ and FeCl₃.
如果金属可能形成一种以上离子，必须包括罗马数字。例如，氧化亚铁与盐酸反应生成氯化亚铁，而氧化铁与盐酸反应生成氯化铁。不要混淆二者，因为它们的化学式不同：FeCl₂ 和 FeCl₃。
5. Worked Examples: Copper(II) Oxide and Magnesium Oxide | 例题：氧化铜与氧化镁
r(II) oxide + sulfuric acid → copper(II) sulfate + water. The balanced symbol equation is:
例 1：氧化铜与稀硫酸反应。文字方程式为：氧化铜 + 硫酸 → 硫酸铜 + 水。配平的符号方程式为：
CuO + H₂SO₄ → CuSO₄ + H₂O
In this reaction, the black copper(II) oxide powder dissolves and the solution turns blue. The blue colour is due to copper(II) ions in solution. This is a classic observation question in practical exams.
在这个反应中，黑色氧化铜粉末溶解，溶液变成蓝色。蓝色来自溶液中的铜(II)离子。这是实验考试中经典的观察题。
m oxide + hydrochloric acid → magnesium chloride + water. The balanced symbol equation is:
例 2：氧化镁与稀盐酸反应。文字方程式为：氧化镁 + 盐酸 → 氯化镁 + 水。配平的符号方程式为：
MgO + 2HCl → MgCl₂ + H₂O
The white magnesium oxide dissolves to form a colourless solution. The test tube may become slightly warm because neutralisation is exothermic. No gas is produced, which helps distinguish this reaction from a metal-carbonate reaction.
白色氧化镁溶解，形成无色溶液。试管可能略微变热，因为中和反应是放热的。该反应不产生气体，这有助于把它与金属碳酸盐的反应区分开来。
Example 3: Iron(III) oxide reacts with hydrochloric acid. The balanced equation is:
例 3：氧化铁与盐酸反应。配平方程式为：
Fe₂O₃ + 6HCl → 2FeCl₃ + 3H₂O
The red-brown iron(III) oxide dissolves and the solution becomes yellow. The yellow colour is due to iron(III) ions. This example is often used to test balancing skills because the coefficients are larger.
红棕色氧化铁溶解，溶液变成黄色。黄色来自铁(III)离子。这个例子常用于测试配平能力，因为系数较大。
6. Writing Symbol Equations and Balancing | 书写并配平符号方程式
To write a balanced symbol equation for a metal oxide and an acid, follow a careful sequence. First, write the correct formulae for the reactants and products. Second, balance the metal atoms. Third, balance the oxygen atoms. Fourth, balance the hydrogen atoms. Finally, check that the chlorine, sulfur, nitrogen or other non-metal atoms are also balanced.
书写金属氧化物与酸反应的配平符号方程式时，要遵循一个严谨的顺序。首先，写出反应物和产物的正确化学式。其次，配平金属原子。第三，配平氧原子。第四，配平氢原子。最后，检查氯、硫、氮或其他非金属原子是否也已配平。
water. The unbalanced skeleton is Al₂O₃ + HCl → AlCl₃ + H₂O. After balancing, it becomes:
例如，氧化铝与盐酸反应生成氯化铝和水。未配平的骨架式是 Al₂O₃ + HCl → AlCl₃ + H₂O。配平后变为：
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
tial because examiners often award marks for correct balancing, not just correct formulae.
检查原子数：Al 2 = 2，O 3 = 3，H 6 = 6，Cl 6 = 6。这个检查非常必要，因为考官通常会给配平正确的答案分数，而不仅仅是化学式正确。
Remember that you must never change a chemical formula to balance an equation. You can only change the coefficient in front of a formula. For example, changing H₂O to H₃O would be wrong because it changes the substance.
记住，绝不能为了配平方程式而改变化学式。你只能改变化学式前面的系数。例如，把 H₂O 改成 H₃O 是错误的，因为那会改变物质本身。
7. Ionic Equations for the Reaction | 反应的离子方程式
In ionic terms, the oxide ion (O²⁻) in the metal oxide accepts protons (H⁺) from the acid to form water. If the metal oxide is insoluble, it is written as the solid formula because it does not dissociate into ions in water. The spectator ions, such as Cl⁻ or SO₄²⁻, are omitted.
从离子角度看，金属氧化物中的氧离子 (O²⁻) 接受酸中的质子 (H⁺) 生成水。如果金属氧化物不溶于水，就写成固体化学式，因为它在水中不会解离成离子。旁观离子，例如 Cl⁻ 或 SO₄²⁻，要省略。
For copper(II) oxide and sulfuric acid, the full ionic equation is:
对于氧化铜与硫酸，完整的离子方程式为：
CuO(s) + 2H⁺(aq) → Cu²⁺(aq) + H₂O(l)
For magnesium oxide and hydrochloric acid, the ionic equation is:
对于氧化镁与盐酸，离子方程式为：
MgO(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂O(l)
Notice that the chloride ions are not shown because they do not change during the reaction. They are present before and after the reaction, so they are spectator ions. Writing ionic equations helps explain why the reaction happens: the oxide ion is a base that neutralises hydrogen ions.
注意氯离子没有出现，因为它们在反应过程中没有变化。它们在反应前后都存在，所以是旁观离子。书写离子方程式有助于解释反应为什么发生：氧离子是一种碱，能中和氢离子。
8. Experiments: Preparing a Soluble Salt | 实验：制备可溶性盐
One important practical use of this reaction is preparing a soluble salt from an insoluble metal oxide. The method has several clear steps. First, measure a fixed volume of dilute acid into a beaker. Second, warm the acid gently if the reaction is slow. Third, add the metal oxide powder in small portions until some solid remains undissolved. Fourth, filter the mixture to remove the excess metal oxide. Fifth, evaporate the filtrate to the crystallisation point. Finally, leave the solution to crystallise, then filter and dry the crystals.
这个反应的一个重要实际用途是从不溶性金属氧化物制备可溶性盐。该方法有几个清晰的步骤。首先，用量筒量取一定体积的稀酸倒入烧杯中。其次，如果反应较慢，可轻微加热酸。第三，少量多次加入金属氧化物粉末，直到有一些固体未溶解。第四，过滤混合物以除去过量的金属氧化物。第五，蒸发滤液至结晶点。最后，让溶液结晶，然后过滤并干燥晶体。
Why must excess metal oxide be added? Because the metal oxide is insoluble, adding it in excess ensures that all the acid has reacted. Any unreacted solid can then be filtered off, leaving a pure salt solution. If excess acid were used instead, the acid would remain in the solution and contaminate the salt.
为什么要加入过量的金属氧化物？因为金属氧化物不溶于水，加入过量可以确保所有酸都已反应。任何未反应的固体随后可以过滤除去，留下纯净的盐溶液。如果改用过量酸，酸会留在溶液中并污染盐。
Why is the solution not evaporated to dryness? If it is heated until all the water boils away, the salt may decompose or spit, and impurities may be left behind. It is better to stop heating when crystals begin to appear at the edge of the solution. This point is called the crystallisation point.
为什么不能把溶液蒸干？如果加热到所有水都沸腾消失，盐可能分解或飞溅，杂质也可能残留。更好的做法是当溶液边缘开始出现晶体时停止加热。这个点称为结晶点。
9. Observations and Practical Tips | 实验现象与操作提示
Different metal oxides give different observations. These observations are often worth marks in practical questions. The table below summarises common cases.
不同的金属氧化物会产生不同的实验现象。这些现象在实验题中常常有分。下表总结了常见情况。
- CuO + H₂SO₄: black solid dissolves, blue solution forms. | 氧化铜 + 硫酸：黑色固体溶解，形成蓝色溶液。
- CuO + HCl: black solid dissolves, blue-green solution forms. | 氧化铜 + 盐酸：黑色固体溶解，形成蓝绿色溶液。
- MgO + HCl: white solid dissolves, colourless solution forms; the mixture warms up. | 氧化镁 + 盐酸：白色固体溶解，形成无色溶液；混合物变热。
- Fe₂O₃ + HCl: red-brown solid dissolves, yellow solution forms. | 氧化铁 + 盐酸：红棕色固体溶解，形成黄色溶液。
- ZnO + HCl: white solid dissolves, colourless solution forms. | 氧化锌 + 盐酸：白色固体溶解，形成无色溶液。
Practical tips: use dilute acid unless the instructions say otherwise; stir the mixture to speed up the reaction; warm gently, but do not boil; add the solid slowly to avoid a violent reaction; and always wear safety goggles because acids are corrosive.
操作提示：除非说明另有要求，否则使用稀酸；搅拌混合物以加快反应；轻微加热，但不要煮沸；缓慢加入固体以避免剧烈反应；始终佩戴护目镜，因为酸有腐蚀性。
Another useful tip is to test the
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