Sulfur and its Oxides | 硫及其氧化物

📚 Sulfur and its Oxides | 硫及其氧化物

Sulfur is a yellow non-metal in Group 16 of the Periodic Table. It forms two important acidic oxides, sulfur dioxide (SO₂) and sulfur trioxide (SO₃). Both oxides are closely linked to industrial processes, redox chemistry and environmental issues such as acid rain.

硫是元素周期表第 16 族的一种黄色非金属。它形成两种重要的酸性氧化物——二氧化硫（SO₂）和三氧化硫（SO₃）。这两种氧化物都与工业过程、氧化还原化学以及酸雨等环境问题密切相关。

1. Occurrence and Extraction of Sulfur | 硫的来源与提取

Sulfur occurs naturally in volcanic regions and in underground deposits. It is also found in metal sulfide ores such as galena (PbS), zinc blende (ZnS) and iron pyrites (FeS₂). Crude oil and natural gas often contain hydrogen sulfide (H₂S), from which sulfur can be recovered.

硫天然存在于火山地区和地下矿床中。它也存在于方铅矿（PbS）、闪锌矿（ZnS）和黄铁矿（FeS₂）等金属硫化物矿石中。原油和天然气通常含有硫化氢（H₂S），可以从中回收硫。

In the Frasch process, superheated water at about 170 °C is pumped into underground sulfur deposits. The sulfur melts and is forced to the surface with compressed air. This produces sulfur of very high purity.

在弗拉施法中，约 170 °C 的过热水被注入地下硫矿床。硫熔化后被压缩空气压到地表，从而得到高纯度硫。

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2. Allotropes of Sulfur | 硫的同素异形体

Sulfur has several allotropes. The most stable form at room temperature is rhombic sulfur (α-sulfur), which consists of crown-shaped S₈ molecules arranged in a rhombic crystal system. Above about 96 °C it slowly changes into monoclinic sulfur (β-sulfur), which also contains S₈ rings but packed in needle-like crystals.

硫有几种同素异形体。室温下最稳定的是斜方硫（α-硫），它由皇冠形的 S₈ 分子组成，晶体属斜方晶系。在约 96 °C 以上它会缓慢转变为单斜硫（β-硫），同样含有 S₈ 环，但晶体呈针状排列。

When molten sulfur is heated above about 160 °C, the S₈ rings break open and polymerise into long chains. If this viscous liquid is poured into cold water, plastic sulfur forms as a rubber-like solid with long chain molecules.

当熔融硫被加热到约 160 °C 以上时，S₈ 环打开并聚合成长链。如果将这种粘稠液体倒入冷水中，就会形成具有长链分子的橡胶状固体——弹性硫。

These allotropes have identical chemical properties because they contain the same element, but their physical properties differ due to different molecular arrangements.

这些同素异形体具有相同的化学性质，因为它们由同一种元素组成；但由于分子排列方式不同，它们的物理性质有所差异。

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3. Combustion of Sulfur | 硫的燃烧

Sulfur burns in air or oxygen with a characteristic blue flame to form sulfur dioxide gas. The reaction is exothermic and is the first stage in the industrial production of sulfuric acid.

硫在空气或氧气中燃烧，产生特征性的蓝色火焰，生成二氧化硫气体。该反应放热，是工业制硫酸的第一阶段。

S(s) + O₂(g) → SO₂(g)

In a limited supply of oxygen, sulfur dioxide is the main product. Further oxidation to sulfur trioxide requires a catalyst and higher temperatures, as discussed in the Contact process.

在氧气供应有限时，主要产物是二氧化硫。要进一步氧化为三氧化硫，则需要催化剂和较高温度，如接触法中所述。

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4. Physical Properties and Laboratory Preparation of Sulfur Dioxide | 二氧化硫的物理性质与实验室制备

Sulfur dioxide is a colourless gas with a sharp, choking smell. It is toxic if inhaled in large amounts and is about 2.26 times denser than air.

二氧化硫是一种无色气体，具有强烈刺激性气味。大量吸入有毒，密度约为空气的 2.26 倍。

It is very soluble in water, and its solubility decreases as temperature rises. The gas can be liquefied easily under pressure, with a boiling point of about −10 °C.

它极易溶于水，且溶解度随温度升高而降低。该气体在加压下容易液化，沸点约为 −10 °C。

In the laboratory, sulfur dioxide is conveniently prepared by adding dilute hydrochloric acid to sodium sulfite, or by heating copper turnings with concentrated sulfuric acid.

在实验室中，通常将稀盐酸加入亚硫酸钠中，或用浓硫酸加热铜屑来制备二氧化硫。

Na₂SO₃ + 2HCl → 2NaCl + SO₂ + H₂O

Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O

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5. Sulfur Dioxide as an Acidic Oxide | 二氧化硫作为酸性氧化物

Sulfur dioxide dissolves in water to form sulfurous acid, H₂SO₃. This is a weak dibasic acid, so the solution turns blue litmus red.

二氧化硫溶于水生成亚硫酸 H₂SO₃。这是一种弱二元酸，因此溶液能使蓝色石蕊试纸变红。

SO₂(g) + H₂O(l) ⇌ H₂SO₃(aq)

As an acidic oxide, SO₂ reacts with alkalis to form sulfite and hydrogensulfite salts. With excess sodium hydroxide, sodium sulfite is formed; with an equimolar amount, sodium hydrogensulfite is produced.

作为酸性氧化物，SO₂ 与碱反应生成亚硫酸盐和亚硫酸氢盐。与过量氢氧化钠反应生成亚硫酸钠；与等物质的量反应则生成亚硫酸氢钠。

SO₂ + 2NaOH → Na₂SO₃ + H₂O

SO₂ + NaOH → NaHSO₃

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6. Sulfur Dioxide as a Reducing Agent | 二氧化硫作为还原剂

The sulfur atom in SO₂ has an oxidation state of +4. It can be oxidised to +6 in SO₄²⁻, so SO₂ is an important reducing agent in aqueous solution.

SO₂ 中硫原子的氧化态为 +4。它可以被氧化为 SO₄²⁻ 中的 +6 态，因此 SO₂ 在水溶液中是一种重要的还原剂。

With acidified potassium manganate(VII), the purple solution is decolourised as MnO₄⁻ is reduced to Mn²⁺ ions.

与酸化高锰酸钾溶液反应时，紫色溶液褪色，因为 MnO₄⁻ 被还原为 Mn²⁺ 离子。

2MnO₄⁻ + 5SO₂ + 2H₂O → 2Mn²⁺ + 5SO₄²⁻ + 4H⁺

With acidified potassium dichromate(VI), the orange solution turns green because Cr(VI) is reduced to Cr(III). This colour change is a useful test for a reducing gas such as SO₂.

与酸化重铬酸钾（VI）溶液反应时，橙色溶液变为绿色，因为 Cr(VI) 被还原为 Cr(III)。这种颜色变化是检验 SO₂ 等还原性气体的有效方法。

Cr₂O₇²⁻ + 3SO₂ + 2H⁺ → 2Cr³⁺ + 3SO₄²⁻ + H₂O

Sulfur dioxide also reduces iron(III) ions to iron(II) ions. This reaction is used in some redox titrations and shows the reducing character of SO₂.

二氧化硫还能将铁（III）离子还原为铁（II）离子。该反应用于一些氧化还原滴定中，体现了 SO₂ 的还原性。

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