A-Level Chemistry: Properties and Uses of Sulfuric Acid | A-Level化学：硫酸的性质与用途

📚 A-Level Chemistry: Properties and Uses of Sulfuric Acid | A-Level化学：硫酸的性质与用途

Sulfuric acid, H₂SO₄, is one of the most important industrial chemicals in the world. In A-Level chemistry, you need to understand its physical properties, its behaviour as an acid, a dehydrating agent and an oxidising agent, and how it is manufactured by the Contact Process.

硫酸（H₂SO₄）是世界上最重要的工业化学品之一。在A-Level化学中，你需要掌握它的物理性质、作为酸、脱水剂和氧化剂的行为，以及通过接触法（Contact Process）制造的工艺。

1. Physical Properties and Structure | 物理性质与结构

Pure sulfuric acid is a dense, colourless, oily liquid with a molar mass of 98.1 g mol⁻¹. It has a high boiling point of about 337 °C, which means it is much less volatile than water and can be used to displace more volatile acids from their salts.

纯硫酸是一种密度大、无色、油状的液体，摩尔质量为98.1 g mol⁻¹。它的沸点约为337 °C，比水难挥发得多，因此可以用来从盐中置换出更易挥发的酸。

The molecule has a tetrahedral arrangement around the sulfur atom. Sulfur is bonded to two hydroxyl groups and two oxygen atoms by double bonds. In aqueous solution, sulfuric acid ionises in two stages because it is a dibasic acid.

在硫酸分子中，硫原子周围呈四面体排布。硫与两个羟基成单键，并与两个氧原子以双键结合。在水溶液中，硫酸作为二元酸分两步电离。

H₂SO₄(aq) → H⁺(aq) + HSO₄⁻(aq)

HSO₄⁻(aq) ⇌ H⁺(aq) + SO₄²⁻(aq)

The first ionisation is complete, and the second is partial. Therefore dilute sulfuric acid contains H⁺, HSO₄⁻ and SO₄²⁻ ions, along with water molecules.

第一步电离完全，第二步电离部分进行。因此稀硫酸中含有H⁺、HSO₄⁻和SO₄²⁻离子，以及水分子。

2. Acidic Properties: Reaction with Bases | 酸性：与碱的反应

Sulfuric acid is a strong acid, so dilute H₂SO₄ reacts readily with bases to form salts and water. Because it is dibasic, it can form two series of salts: normal sulfates and hydrogen sulfates.

硫酸是一种强酸，因此稀H₂SO₄能与碱迅速反应生成盐和水。由于它是二元酸，可以形成两类盐：正盐硫酸盐和酸式盐硫酸氢盐。

With sodium hydroxide, the reaction depends on the mole ratio. With two moles of NaOH, sodium sulfate is formed:

与氢氧化钠反应时，产物取决于物质的量之比。当NaOH为两摩尔时，生成硫酸钠：

2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)

With only one mole of NaOH per mole of acid, sodium hydrogen sulfate is produced:

当每摩尔酸只与一摩尔NaOH反应时，生成硫酸氢钠：

NaOH(aq) + H₂SO₄(aq) → NaHSO₄(aq) + H₂O(l)

Sulfuric acid also neutralises ammonia to give ammonium sulfate, a widely used fertiliser:

硫酸还能与氨发生中和反应，生成广泛使用的肥料——硫酸铵：

2NH₃(aq) + H₂SO₄(aq) → (NH₄)₂SO₄(aq)

3. Reaction with Metals and Carbonates | 与金属和碳酸盐的反应

Dilute sulfuric acid reacts with reactive metals such as magnesium and zinc to release hydrogen gas. For example, with magnesium:

稀硫酸能与镁、锌等活泼金属反应并放出氢气。例如与镁的反应：

Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g)

However, lead and calcium are problematic because their sulfates are insoluble. The formation of an insoluble layer of PbSO₄ or CaSO₄ slows or stops the reaction.

但铅和钙的情况比较特殊，因为它们的硫酸盐不溶于水。反应中生成的不溶性PbSO₄或CaSO₄层会减慢甚至阻止反应继续进行。

With carbonates and hydrogen carbonates, dilute sulfuric acid produces carbon dioxide, water and a salt. For example:

稀硫酸与碳酸盐、碳酸氢盐反应生成二氧化碳、水和盐。例如：

Na₂CO₃(s) + H₂SO₄(aq) → Na₂SO₄(aq) + H₂O(l) + CO₂(g)

These reactions are useful in qualitative analysis. The effervescence of CO₂ when an unknown carbonate is treated with dilute acid is a classic test.

这些反应在定性分析中很有用。用稀酸处理未知碳酸盐时产生CO₂气泡，是经典的检验方法。

4. Dehydrating Agent | 脱水剂

Concentrated sulfuric acid has a strong affinity for water. As a dehydrating agent, it removes the elements of water from covalent compounds, even when water molecules are not actually present.

浓硫酸对水有很强的亲和力。作为脱水剂，它可以从共价化合物中夺取水的组成元素，即使化合物中并不存在真正的水分子。

For example, when concentrated H₂SO₄ is added to sucrose, C₁₂H₂₂O₁₁, the sugar is dehydrated to black carbon:

例如，将浓H₂SO₄加入蔗糖（C₁₂H₂₂O₁₁）中，蔗糖会被脱水变成黑色的碳：

C₁₂H₂₂O₁₁(s) → 12C(s) + 11H₂O(g)

The reaction produces steam, and the evolving gas also contains SO₂ from the further oxidation of carbon by concentrated sulfuric acid. The black, swollen solid is a familiar demonstration of dehydration.

该反应会放出水蒸气，同时由于浓硫酸进一步氧化碳，气体中还含有SO₂。黑色膨胀的固体是脱水作用的经典演示实验。

Concentrated sulfuric acid also dehydrates hydrated copper(II) sulfate and many organic compounds such as ethanol. When ethanol is heated with concentrated H₂SO₄ at about 170 °C, ethene is formed:

浓硫酸还能使五水硫酸铜等结晶水合物脱水，也能使乙醇等有机化合物脱水。当乙醇与浓H₂SO₄在约170 °C下加热时，生成乙烯：

C₂H₅OH(l) → C₂H₄(g) + H₂O(l)

This is why concentrated H₂SO₄ is used as a catalyst and dehydrating agent in the laboratory preparation of alkenes.

这也是浓H₂SO₄在实验室制备烯烃时被用作催化剂和脱水剂的原因。

5. Oxidising Agent | 氧化剂

Hot concentrated sulfuric acid is a powerful oxidising agent. In these reactions the sulfur in H₂SO₄ is reduced, usually from the +6 oxidation state to +4 in sulfur dioxide, SO₂.

热浓硫酸是一种强氧化剂。在这些反应中，H₂SO₄中的硫被还原，通常从+6氧化态降到SO₂中的+4氧化态。

It oxidises metals such as copper, which cannot react with dilute acid. The equation is:

它能够氧化铜等不能与稀酸反应的金属，反应方程式为：

Cu(s) + 2H₂SO₄(conc) → CuSO₄(aq) + SO₂(g) + 2H₂O(l)

Zinc and carbon are also oxidised. With carbon, the products are carbon dioxide, sulfur dioxide and water:

锌和碳也能被氧化。碳与浓硫酸反应生成二氧化碳、二氧化硫和水：

C(s) + 2H₂SO₄(conc) → CO₂(g) + 2SO₂(g) + 2H₂O(l)

Concentrated H₂SO₄ can also oxidise hydrogen halides. It oxidises hydrogen bromide to bromine, and hydrogen iodide to iodine, while itself being reduced to SO₂.

浓H₂SO₄还能氧化卤化氢。它可以把溴化氢氧化为溴，把碘化氢氧化为碘，自身被还原为SO₂。

2HBr + H₂SO₄(conc) → Br₂ + SO₂ + 2H₂O

Because of this oxidising behaviour, concentrated H₂SO₄ cannot be used to prepare HBr or HI from their salts, although it can be used for HCl, which is not oxidised.

由于具有氧化性，不能用浓H₂SO₄从盐中制备HBr或HI，但可以用于制备不被氧化的HCl。

6. Sulphonation and Esterification | 磺化与酯化

Sulfuric acid is an important reagent in organic chemistry. It acts as a catalyst in esterification, for example in the preparation of ethyl ethanoate from ethanol and ethanoic acid.

硫酸是有机化学中的重要试剂。它在酯化反应中作催化剂，例如由乙醇和乙酸制备乙酸乙酯。

It also participates in sulfonation. When benzene is heated with concentrated sulfuric acid, or with fuming sulfuric acid, benzenesulfonic acid is formed:

它还参与磺化反应。当苯与浓硫酸或发烟硫酸加热时，生成苯磺酸：

C₆H₆ + H₂SO₄(conc) → C₆H₅SO₃H + H₂O

This electrophilic substitution reaction is industrial important in the production of detergents and dyes. The sulfonic acid group –SO₃H makes the molecule more soluble in water.

这个亲电取代反应在工业上对洗涤剂和染料的生产很重要。磺酸基（–SO₃H）能增加分子在水中的溶解度。

In the Contact Process, concentrated sulfuric acid is also used to absorb sulfur trioxide. The SO₃ cannot be absorbed directly in water because it forms a fine mist of sulfuric acid that is difficult to condense. Instead, it is absorbed in concentrated H₂SO₄ to form oleum, H₂S₂O₇:

在接触法中，浓硫酸还用于吸收三氧化硫。SO₃不能直接用水吸收，因为会形成难以凝聚的硫酸酸雾。因此，SO₃被吸收在浓H₂SO₄中形成发烟硫酸（H₂S₂O₇）：

SO₃(g) + H₂SO₄(l) → H₂S₂O₇(l)

The oleum is then carefully diluted with water to give more sulfuric acid:

随后将发烟硫酸小心地用水稀释，得到更多的硫酸：

H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(l)

7. Manufacture: The Contact Process | 工业制造：接触法

Almost all sulfuric acid is manufactured by the Contact Process. The starting material is sulfur, which is burned in air to produce sulfur dioxide:

几乎所有的硫酸都通过接触法制造。原料硫在空气中燃烧生成二氧化硫：

S(s) + O₂(g) → SO₂(g)

In many plants, SO₂ is also obtained by roasting sulfide ores such as zinc blende, ZnS. The sulfur dioxide is then oxidised to sulfur trioxide in the presence of a vanadium(V) oxide catalyst:

在许多工厂中，SO₂也通过焙烧闪锌矿（ZnS）等硫化物矿获得。随后，二氧化硫在五氧化二钒催化剂存在下被氧化为三氧化硫：

2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −196 kJ mol⁻¹

The forward reaction is exothermic and produces fewer moles of gas. According to Le Chatelier’s principle, low temperature and high pressure favour a high yield of SO₃. In practice, a temperature of about 450 °C is used, with a pressure of 1–2 atm and a V₂O₅ catalyst.

正反应放热，且气体分子数减少。根据勒夏特列原理，低温和高压有利于提高SO₃的产率。实际生产中采用约450 °C的温度、1–2 atm的压力以及V₂O₅催化剂。

An intermediate temperature is chosen as a compromise: lower temperatures give a better equilibrium yield but a slower rate. The catalyst helps the reaction reach equilibrium quickly. Excess oxygen is used to drive the equilibrium to the right.

选择中等温度是折衷方案：较低温度平衡产率更高但速率太慢，催化剂则帮助反应快速达到平衡。使用过量氧气可以推动平衡向右移动。

Finally, the SO₃ is absorbed in concentrated H₂SO₄ to form oleum, which is then diluted with water to form sulfuric acid of the required concentration.

最后，SO₃被吸收在浓H₂SO₄中形成发烟硫酸，再用水稀释成所需浓度的硫酸。

8. Uses in Industry and the Laboratory | 工业与实验室中的用途

Sulfuric acid is often described as the “king of chemicals” because it is used in more industrial processes than almost any other compound. Its largest use is in the manufacture of phosphate fertilisers such as ammonium sulfate and superphosphate.

硫酸常被称为“化学工业之母”，因为它参与比几乎任何其他化合物都要多的工业过程。其最大用途是制造磷肥、硫酸铵等肥料。

Other major uses include:

其他主要用途包括：

Manufacture of paints, pigments and dyes.

制造涂料、颜料和染料。
Production of detergents and synthetic resins.

生产洗涤剂和合成树脂。
Electrolyte in lead-acid storage batteries.

用作铅酸蓄电池中的电解质。
Refining petroleum and removing impurities from oils.

石油精炼以及去除油品中的杂质。
Laboratory reagent for preparing gases, esters and as a dehydrating agent.

实验室中用于制备气体、酯，以及作为脱水剂。
Cleaning and pickling metal surfaces before electroplating.

电镀前对金属表面进行清洗和酸洗。

Sulfuric acid is also used in the manufacture of other acids, such as nitric acid, by displacing the more volatile acid from its salt:

硫酸还可通过置换挥发性酸的方法制备其他酸，例如硝酸：

NaNO₃(s) + H₂SO₄(conc) → NaHSO₄(s) + HNO₃(g)

9. Safety and Environmental Considerations | 安全与环境考量

Concentrated sulfuric acid is highly corrosive. It causes severe burns on contact with skin and eyes. It also reacts violently with water, releasing a great deal of heat. Therefore, when diluting, the acid must be added slowly to water with constant stirring, never water to acid.

浓硫酸具有强腐蚀性，接触皮肤和眼睛会造成严重灼伤。它与水反应剧烈并放出大量热。因此稀释时，必须将酸缓慢加入水中并不断搅拌，绝不能将水加入酸中。

Fumes of SO₂ and SO₃ are harmful. The Contact Process is designed to minimise the release of SO₂, and modern plants use catalytic converters or scrubbing systems to remove sulfur dioxide from waste gases.

SO₂和SO₃的烟雾有害健康。接触法工艺设计上尽量减少SO₂的排放，现代化工厂使用催化转化器或洗涤系统脱除废气中的二氧化硫。

Many raw materials for sulfuric acid, such as sulfur or sulfide ores, contain impurities. When these are burned, the SO₂ produced must be cleaned before entering the converter, because impurities can poison the vanadium(V) oxide catalyst.

许多硫酸原料，如硫或硫化物矿，含有杂质。这些原料燃烧时产生的SO₂在进入转化器之前必须先净化，因为杂质会使五氧化二钒催化剂中毒。

In the laboratory, spills should be neutralised carefully with sodium carbonate or another weak base, and protective equipment such as chemical-resistant gloves and safety goggles should always be worn.

实验室中，硫酸泄漏应用碳酸钠等弱碱小心中和，操作时始终应佩戴耐化学品手套和护目镜等防护设备。

10. Summary of Key Reactions | 重点反应总结

The table below summarises the key reactions of sulfuric acid that you need to remember for CIE A-Level chemistry.

下表总结了你在CIE A-Level化学中需要记住的硫酸关键反应。

Type of behaviour	Reaction example	Observations
Strong acid	Mg + H₂SO₄ → MgSO₄ + H₂	Effervescence, gas burns with a pop
Dehydrating agent	C₁₂H₂₂O₁₁ → 12C + 11H₂O	Black carbon forms
Oxidising agent	Cu + 2H₂SO₄(conc) → CuSO₄ + SO₂ + 2H₂O	SO₂ smell, blue solution forms
Sulphonating agent	C₆H₆ + H₂SO₄ → C₆H₅SO₃H + H₂O	Water-soluble sulfonic acid formed

Remember that dilute H₂SO₄ is primarily an acid, while concentrated H₂SO₄ shows the additional dehydrating and oxidising properties. Being able to distinguish between these roles is essential for exams.

请记住，稀H₂SO₄主要表现为酸性，而浓H₂SO₄还表现出脱水性和氧化性。能够区分这些角色是考试的关键。

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A-Level Chemistry: Properties and Uses of Sulfuric Acid | A-Level化学：硫酸的性质与用途