📚 Ammonia and Ammonium Compounds | 氨和铵化合物
Ammonia is a colourless, pungent-smelling gas with the formula NH₃. It is one of the most important industrial chemicals, serving as the foundation for a vast array of products, from agricultural fertilizers to household cleaners. The chemistry of ammonia is closely linked to ammonium compounds, which contain the NH₄⁺ ion. In the Cambridge International A-Level curriculum, a thorough understanding of the preparation, properties, reactions, and uses of ammonia and its salts is essential for mastering the inorganic and physical chemistry components.
氨是一种无色、有刺激性气味的气体，化学式为 NH₃。它是最重要的工业化学品之一，是众多产品的基础，从农业肥料到家用清洁剂都离不开它。氨的化学性质与铵化合物密切相关，铵化合物含有 NH₄⁺ 离子。在剑桥国际 A-Level 课程中，透彻理解氨及其盐的制备方法、性质、反应和用途，对于掌握无机化学和物理化学部分至关重要。
1. Introduction to Ammonia | 氨简介
Ammonia is a covalent compound composed of one nitrogen atom covalently bonded to three hydrogen atoms, with a lone pair of electrons on the nitrogen. This lone pair is responsible for ammonia's characteristic behaviour as a Brønsted–Lowry base and as a ligand in complex ion formation. The molecule has a trigonal pyramidal geometry with bond angles of approximately 107°, slightly less than the ideal tetrahedral angle due to lone-pair repulsion. In the laboratory and in industry, ammonia is encountered as a gas, an aqueous solution, and as a refrigerant.
氨是一种共价化合物，由一个氮原子通过共价键与三个氢原子结合，氮上带有一对孤对电子。这对孤对电子赋予了氨作为 Brønsted–Lowry 碱以及作为配体形成配合物的典型行为。氨分子呈三角锥形几何构型，键角约为 107°，由于孤对电子的排斥作用，略小于理想四面体角。在实验室和工业中，氨以气体、水溶液以及制冷剂的形式出现。
Ammonium compounds, on the other hand, contain the polyatomic ammonium ion NH₄⁺. This ion is formed when ammonia accepts a proton (H⁺) via its lone pair, acting as a base. The ammonium ion is tetrahedral and is isoelectronic with methane. It forms a wide range of salts with anions such as chloride, sulfate, nitrate and phosphate, many of which are highly soluble in water and thermally unstable.
另一方面，铵化合物含有多原子铵离子 NH₄⁺。该离子是氨通过其孤对电子接受一个质子 (H⁺) 作为碱而形成的。铵离子呈四面体形，与甲烷是等电子体。它与氯离子、硫酸根离子、硝酸根离子和磷酸根离子等阴离子形成多种盐，其中许多盐在水中的溶解度很高，且热稳定性差。
2. Laboratory Preparation of Ammonia | 氨的实验室制备
In the laboratory, ammonia gas is conveniently produced by heating a mixture of an ammonium salt and a strong base. The classic method involves ammonium chloride and calcium hydroxide (slaked lime). The equation for the reaction is:
在实验室里，氨气可通过加热铵盐和强碱的混合物方便地制取。经典方法使用氯化铵和氢氧化钙（熟石灰）。反应方程式为：
2NH₄Cl(s) + Ca(OH)₂(s) → CaCl₂(s) + 2NH₃(g) + 2H₂O(g)
This reaction is a double displacement followed by decomposition. The mixture is gently heated in a test tube or flask, and the evolved ammonia gas is collected by downward delivery (upward displacement of air), because ammonia is less dense than air. The gas is dried by passing it through a tower packed with calcium oxide (quicklime) granules; concentrated sulfuric acid or phosphorus(V) oxide cannot be used as drying agents because they would react with the basic ammonia.
该反应是先发生复分解反应继而分解。将混合物在试管或烧瓶中缓缓加热，产生的氨气因密度小于空气，用向下排空气法（向上排空气）收集。气体经过填充有氧化钙（生石灰）颗粒的干燥塔进行干燥；不能使用浓硫酸或五氧化二磷作为干燥剂，因为它们会与碱性的氨发生反应。
An alternative laboratory route uses the reaction of ammonium sulfate with sodium hydroxide, but the principle remains the same. The moisture from the water vapour produced is removed by the alkaline drying agent. The characteristic pungent odour and the ability to turn damp red litmus paper blue confirm the presence of ammonia.
另一种实验室方法是使用硫酸铵与氢氧化钠反应，但原理相同。产生的水蒸气中的水分被碱性干燥剂除去。特有的刺激性气味以及能使湿润的红色石蕊试纸变蓝的性质，可确证氨的存在。
3. Industrial Production: The Haber Process | 工业生产：哈伯法
Ammonia is manufactured globally on a massive scale through the Haber process, which combines nitrogen from the air and hydrogen derived mainly from natural gas (methane). The reversible exothermic reaction is represented by:
氨通过哈伯法在全球范围内大规模生产，该方法将空气中的氮与主要来自天然气（甲烷）的氢相结合。这个可逆的放热反应表示为：
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ mol⁻¹
The equilibrium position is favoured by high pressure and low temperature according to Le Chatelier’s principle. However, a compromise set of conditions is applied to achieve an economically viable rate of reaction. The typical industrial parameters are: a pressure of 200–300 atm, a temperature of 400–450°C, and the use of a finely divided iron catalyst with promoters such as potassium oxide and aluminium oxide.
根据勒夏特列原理，高压和低温有利于平衡向右移动。然而，为了获得经济上可行的反应速率，必须采用一个折中的条件。典型的工业参数为：压力 200–300 大气压，温度 400–450°C，并使用以氧化钾和氧化铝为促进剂的细碎铁催化剂。
The hydrogen is produced via steam reforming of methane: CH₄ + H₂O ⇌ CO + 3H₂, followed by a shift reaction to increase yield. The nitrogen is obtained from the fractional distillation of liquid air. Only about 15–20% conversion is achieved per pass through the reactor, so the unreacted gases are recycled after the ammonia is condensed out. The process exemplifies the application of equilibrium and kinetics principles in green chemistry and cost-effective manufacturing.
氢气通过甲烷的水蒸气重整制得：CH₄ + H₂O ⇌ CO + 3H₂，随后通过变换反应提高产率。氮气则来自液态空气的分馏。每次通过反应器只有约 15–20% 的转化率，因此未反应的气体在氨冷凝后被循环利用。该过程体现了平衡和动力学原理在绿色化学和成本效益生产中的应用。
4. Physical Properties of Ammonia | 氨的物理性质
Ammonia is a colourless gas at room temperature with a characteristically sharp, choking odour. It is less dense than air (molar mass 17.0 g mol⁻¹ versus air’s approximate 29 g mol⁻¹), which is why it is collected by downward delivery. It is highly soluble in water, with a solubility of approximately 1 volume of water dissolving 1300 volumes of ammonia gas at 0°C, making it one of the most soluble gases known. The dissolution is exothermic and involves hydrogen bonding between ammonia and water molecules.
氨在室温下是一种无色气体，具有特有的尖刺、窒息性气味。其密度比空气小（摩尔质量为 17.0 g mol⁻¹，而空气约为 29 g mol⁻¹），因此用向下排空气法收集。氨极易溶于水，在 0°C 时约 1 体积水可溶解 1300 体积氨气，是已知溶解度最大的气体之一。溶解过程放热，并涉及氨与水分子之间的氢键作用。
The boiling point of liquid ammonia is −33.3°C. Liquid ammonia is a useful solvent and is commonly used as a refrigerant (R717). When ammonia gas is cooled under pressure, it readily liquefies, and its large latent heat of vaporisation makes it effective in refrigeration cycles. The vapour density and diffusion behaviour are in line with Graham's law; ammonia diffuses faster than heavier gases but slower than hydrogen.
液氨的沸点为 −33.3°C。液氨是一种有用的溶剂，并常用作制冷剂 (R717)。氨气在加压冷却时容易液化，其较大的汽化潜热使其在制冷循环中高效工作。其蒸气密度和扩散行为符合格雷姆定律；氨的扩散速率比重气体快，但比氢慢。
5. Chemical Properties: Reactions with Oxygen, Water and Metal Oxides | 化学性质：与氧、水和金属氧化物的反应
Ammonia does not support ordinary combustion in air, but it burns in pure oxygen with a yellowish-green flame, producing nitrogen and water. The reaction is:
氨在空气中不支持普通燃烧，但在纯氧中能燃烧，发出黄绿色火焰，生成氮气和水。反应为：
4NH₃(g) + 3O₂(g) → 2N₂(g) + 6H₂O(g)
re: 4NH₃ + 5O₂ → 4NO + 6H₂O. This demonstrates the reducing power of ammonia. Ammonia also reduces heated metal oxides such as copper(II) oxide to the metal, itself being oxidised to nitrogen:
在铂铑催化剂作用下，氨可在硝酸制造的奥斯特瓦尔德法中被氧化为一氧化氮 (NO)：4NH₃ + 5O₂ → 4NO + 6H₂O。这体现了氨的还原性。氨还能将热的金属氧化物如氧化铜还原为金属，自身被氧化成氮：
2NH₃(g) + 3CuO(s) → 3Cu(s) + N₂(g) + 3H₂O(g)
Ammonia dissolves exothermically in water to form an alkaline solution of ammonium hydroxide, though the equilibrium lies far to the left. The aqueous solution, often called ‘ammonium hydroxide’, contains mainly hydrated ammonia molecules and a small concentration of ammonium and hydroxide ions. The equilibrium is: NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq), which explains the weakly basic nature of the solution.
氨溶于水放热，形成氢氧化铵的碱性溶液，尽管平衡远远偏向左侧。这种水溶液通常称为“氢氧化铵”，主要含有水合氨分子和少量铵离子与氢氧根离子。平衡为：NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)，这解释了该溶液的弱碱性。
6. Ammonia as a Base and Formation of Ammonium Salts | 氨作为碱与铵盐的形成
Ammonia behaves as a Brønsted– ense white smoke of solid ammonium chloride is produced: NH₃(g) + HCl(g) → NH₄Cl(s). This reaction is a classic demonstration of gaseous acid– neutralises acids in solution, producing ammonium salts. For example, with sulfuric acid:
氨表现 Brønsted–Lowry 碱的行为，因为氮原子的孤对电子可以接受质子形成铵离子。当氨气与氯化氢气体反应时，生成浓密的白色固体氯化铵烟雾：NH₃(g) + HCl(g) → NH₄Cl(s)。该反应是气态酸碱结合的经典演示。同样，氨在溶液中与酸中和，生成铵盐。例如与硫酸反应：
2NH₃(aq) + H₂SO₄(aq) → (NH₄)₂SO₄(aq)
The resulting ammonium salts are soluble in water and can be crystallised by evaporation. Ammonia also acts as a nucleophile due to its lone pair, participating in organic substitution reactions to form amines. The basic strength of ammonia in aqueous solution (pKb ≈ 4.75) makes it a convenient weak base for titrations and buffer preparations.
生成的铵盐可溶于水，通过蒸发结晶获得。由于具有孤对电子，氨还可作为亲核试剂参与有机取代反应生成胺类。氨在水溶液中的碱强度 (pKb ≈ 4.75) 使其成为滴定和缓冲液制备中方便的弱碱。
7. Common Ammonium Salts and Their Properties | 常见铵盐及其性质
Ammonium salts are widely used in agriculture, industry, and the laboratory. Key examples include ammonium sulfate ((NH₄)₂SO₄), ammonium nitrate (NH₄NO₃), ammonium chloride (NH₄Cl), ammonium carbonate ((NH₄)₂CO₃), and ammonium phosphate ((NH₄)₃PO₄). All are white crystalline solids with high water solubility. Their solutions are slightly acidic due to hydrolysis of the ammonium ion: NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺, which is why ammonium salts often give pH values around 5 in water.
铵盐广泛用于农业、工业和实验室。主要例子包括硫酸铵 ((NH₄)₂SO₄)、硝酸铵 (NH₄NO₃)、氯化铵 (NH₄Cl)、碳酸铵 ((NH₄)₂CO₃) 和磷酸铵 ((NH₄)₃PO₄)。它们均为白色结晶固体，水溶性高。其水溶液因铵离子水解而略显酸性：NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺，这就是铵盐在水中的 pH 值常在 5 左右的原因。
Ammonium nitrate is a particularly important salt because it serves both as a high-nitrogen fertiliser and as a component in explosives when mixed with fuel oil (ANFO). Ammonium sulfate is a common fertiliser supplying both nitrogen and sulfur. Ammonium chloride is used in dry cell batteries, as a flux in soldering, and as an expectorant in cough medicine. All ammonium salts undergo thermal decomposition, a property frequently examined at A-Level.
硝酸铵是一种特别重要的盐，因为它既可作为高氮肥料，也可与燃油混合制成炸药 (ANFO)。硫酸铵是提供氮和硫的常用肥料。氯化铵用于干电池、焊接助焊剂，并作为咳嗽药中的祛痰成分。所有铵盐都会发生热分解，这一性质在 A-Level 考试中经常考查。
8. Thermal Decomposition of Ammonium Salts | 铵盐的热分解
When heated, ammonium salts decompose in various ways depending on the nature of the anion. Ammonium chloride, for example, appears to sublime – it dissociates reversibly into ammonia and hydrogen chloride gases, which recombine upon cooling. The equation is: NH₄Cl(s) ⇌ NH₃(g) + HCl(g). This is not true sublimation but a reversible chemical decomposition. This property is used to separate ammonium chloride from mixtures.
铵盐加热时的分解方式因阴离子的性质而异。例如，氯化铵似乎会升华——它可逆地离解为氨和氯化氢气体，冷却后重新结合。方程式为：NH₄Cl(s) ⇌ NH₃(g) + HCl(g)。这并不是真正的升华，而是可逆的化学分解。该性质可用于从混合物中分离氯化铵。
). Strong heating or detonation can lead to exothermic decomposition yielding nitrogen, oxygen and water, which is the basis of its explosive behaviour. Ammonium sulfate decomposes above 235°C to give ammonia, nitrogen, sulfur dioxide and water, while ammonium carbonate decomposes readily at room temperature, releasing ammonia, carbon dioxide and water vapour – hence its use in smelling salts.
硝酸铵在缓慢加热时分解生成一氧化二氮（笑气）和水：NH₄NO₃(s) → N₂O(g) + 2H₂O(g)。剧烈加热或引爆会导致放热分解，产生氮气、氧气和水，这是其爆炸性的基础。硫酸铵在 235°C 以上分解生成氨、氮、二氧化硫和水，而碳酸铵在室温下就容易分解，释放氨、二氧化碳和水蒸气——因此它被用于嗅盐。
9. Tests for Ammonium Ions | 铵离子的检验
The classical test for ammonium ions (NH₄⁺) in a solid or solution exploits the liberation of ammonia gas when warmed with a strong alkali. The standard procedure involves adding dilute sodium hydroxide solution to the sample and gently heating. If ammonium ions are present, ammonia gas is evolved, which can be detected by its characteristic odour and by its action on damp red litmus paper, turning it blue. A more reliable test uses a glass rod dipped in concentrated hydrochloric acid held near the mouth of the test tube; dense white fumes of ammonium chloride confirm the presence of ammonia.
检验固体或溶液中铵离子 (NH₄⁺) 的经典方法是利用其与强碱共热时放出氨气。标准操作是向样品中加入稀氢氧化钠溶液并缓缓加热。若存在铵离子，则会释放氨气，可通过其特有气味以及使湿润的红色石蕊试纸变蓝来检测。更可靠的检测方法是用蘸有浓盐酸的玻璃棒靠近试管口；若形成浓密的白色氯化铵烟雾，则确证氨的存在。
). This test is crucial in qualitative analysis schemes to distinguish ammonium salts from other white solids. It is important to note that the solution should be warmed but not boiled vigorously to avoid spitting. The test can be made quantitative by acid–base back titration using standard acid and alkali.
反应的离子方程式为：NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O(l)。该检验在定性分析方案中对于区分铵盐与其他白色固体至关重要。需注意溶液应温热而不要剧烈沸腾，以避免喷溅。该检验可通过使用标准酸碱的反滴定法实现定量化。
10. Uses of Ammonia and Ammonium Compounds | 氨和铵化合物的用途
The overwhelming majority of industrially produced ammonia is converted into fertilisers, either by direct injection into soil or, more commonly, by conversion into ammonium salts and urea. Ammonium nitrate, ammonium sulfate and diammonium phosphate are among the world's most heavily consumed synthetic fertilisers, directly supporting global food production. Ammonia is also a precursor to nitric acid via the Ostwald process, which in turn is used to make explosives, dyes and polymers.
工业生产的氨绝大部分被转化为肥料，或直接施入土壤，或更常见地转化为铵盐和尿素。硝酸铵、硫酸铵和磷酸二铵是全世界消耗量最大的合成肥料之一，直接支撑着全球粮食生产。氨还是通过奥斯特瓦尔德法制造硝酸的前体，而硝酸又用于制造炸药、染料和聚合物。
Liquid ammonia's high heat of vaporisation makes it an effective refrigerant in industrial ice plants and cold storages. Ammonium chloride is essential in dry cell batteries as an electrolyte and in metal treatment as a flux. In the laboratory, ammonia solution is a routinely used weak base and complexing agent; it forms deep blue [Cu(NH₃)₄]²⁺ with copper(II) ions, a characteristic test for copper. Ammonium carbonate is used in the manufacture of smelling salts and as a leavening agent in baking.
液氨的高蒸发热使其成为工业制冰厂和冷库中有效的制冷剂。氯化铵作为电解质在干电池中至关重要，并作为助焊剂用于金属处理。在实验室中，氨溶液是一种经常使用的弱碱和络合剂；它能与铜(II)离子形成深蓝色的 [Cu(NH₃)₄]²⁺ 离子，这是铜的特征检验。碳酸铵用于制造嗅盐，并作为烘焙中的膨松剂。
11. Environmental and Safety Considerations | 环境与安全考量
Ammonia is a toxic gas; exposure to high concentrations can cause severe respiratory damage and even death. It is also corrosive and can cause burns to the skin and eyes. In industrial settings, strict safety protocols, leak detectors, and proper ventilation are mandatory. Ammonia spills in water bodies increase the nitrogen load, contributing to eutrophication – the excessive growth of algae that depletes oxygen and harms aquatic life.
氨是一种有毒气体；高浓度接触可导致严重的呼吸系统损伤甚至死亡。它还具有腐蚀性，可灼伤皮肤和眼睛。在工业环境中，必须严格遵守安全规程、配备泄漏检测器和适当的通风措施。氨泄漏到水体中会增加氮负荷，导致富营养化——藻类过度生长耗尽水中氧气，危害水生生物。
The intensive use of ammonium fertilisers can lead to nitrate runoff into rivers and groundwater, posing health risks such as methemoglobinemia (blue baby syndrome) and acidification of soils. Therefore, sustainable agricultural practices and controlled-release fertilisers are increasingly important. Nevertheless, the Haber process remains indispensable, and ongoing research focuses on reducing its carbon footprint by using renewable hydrogen and more efficient catalysts.
大量使用铵肥会导致硝酸盐径流进入河流和地下水，引发高铁血红蛋白血症（蓝婴综合征）和土壤酸化等健康风险。因此，可持续农业实践和控释肥料日益重要。尽管如此，哈伯法仍然不可或缺，当前研究重点在于利用可再生氢和更高效的催化剂来减少其碳足迹。
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