离子与气体的检验Tests for ions and gases
定性分析通过颜色、沉淀和气体等现象判断物质中含有哪些离子。下表列出焰色反应、阳离子与氢氧化钠溶液和氨水的反应、常见阴离子的检验方法以及常见气体的检验方法。
Qualitative analysis identifies the ions in a substance from colours, precipitates and gases. The tables give flame colours, the reactions of cations with aqueous sodium hydroxide and aqueous ammonia, tests for common anions and tests for common gases.
焰色反应Flame tests
用蘸有盐酸的铂丝或镍铬丝蘸取样品，放在无色火焰中灼烧，观察火焰颜色。
Dip a platinum or nichrome wire moistened with hydrochloric acid into the sample, hold it in a non-luminous flame and observe the colour.
Li⁺洋红色red (crimson)
Na⁺黄色yellow持久明亮的黄色，常掩盖其他离子的焰色persistent bright yellow that masks other colours
K⁺浅紫色lilac透过蓝色钴玻璃观察，以滤去钠的黄光view through blue cobalt glass to filter out sodium's yellow
Ca²⁺砖红色orange-red (brick red)
Sr²⁺洋红色red (crimson)
Ba²⁺黄绿色apple green
Cu²⁺蓝绿色blue-green
阳离子：与氢氧化钠溶液和氨水反应Cations: reactions with aqueous sodium hydroxide and ammonia
| 离子 Ion | 少量 NaOH A little NaOH | 过量 NaOH Excess NaOH | 少量氨水 A little NH₃ | 过量氨水 Excess NH₃ |
|---|---|---|---|---|
| Al³⁺ | 白色沉淀white precipitate | 溶解，得无色溶液dissolves, giving a colourless solution | 白色沉淀white precipitate | 不溶insoluble |
| NH₄⁺ | 无沉淀；加热放出 NH₃no precipitate; NH₃ given off on warming | —— | —— | —— |
| Ca²⁺ | 白色沉淀（溶液浓时）white precipitate (with concentrated solutions) | 不溶insoluble | 无沉淀no precipitate | —— |
| Cr³⁺ | 灰绿色沉淀grey-green precipitate | 溶解，得深绿色溶液dissolves, giving a dark green solution | 灰绿色沉淀grey-green precipitate | 不溶insoluble |
| Cu²⁺ | 浅蓝色沉淀pale blue precipitate | 不溶insoluble | 浅蓝色沉淀pale blue precipitate | 溶解，得深蓝色溶液dissolves, giving a dark blue solution |
| Fe²⁺ | 绿色沉淀，在空气中逐渐变为红褐色green precipitate, turning red-brown on standing in air | 不溶insoluble | 绿色沉淀，在空气中逐渐变为红褐色green precipitate, turning red-brown on standing in air | 不溶insoluble |
| Fe³⁺ | 红褐色沉淀red-brown precipitate | 不溶insoluble | 红褐色沉淀red-brown precipitate | 不溶insoluble |
| Mg²⁺ | 白色沉淀white precipitate | 不溶insoluble | 白色沉淀white precipitate | 不溶insoluble |
| Mn²⁺ | 近白色沉淀，在空气中迅速变为棕色off-white precipitate, rapidly turning brown in air | 不溶insoluble | 近白色沉淀，在空气中迅速变为棕色off-white precipitate, rapidly turning brown in air | 不溶insoluble |
| Zn²⁺ | 白色沉淀white precipitate | 溶解，得无色溶液dissolves, giving a colourless solution | 白色沉淀white precipitate | 溶解，得无色溶液dissolves, giving a colourless solution |
阴离子的检验Tests for anions
| 离子 Ion | 操作 Test | 现象 Result |
|---|---|---|
| CO₃²⁻ | 加入稀酸add dilute acid | 产生气泡；气体使澄清石灰水变浑浊（CO₂）effervescence; the gas turns limewater milky (CO₂) |
| Cl⁻ | 用稀硝酸酸化，加入硝酸银溶液acidify with dilute nitric acid, then add aqueous silver nitrate | 白色沉淀 AgCl，溶于稀氨水white precipitate of AgCl, soluble in dilute ammonia |
| Br⁻ | 用稀硝酸酸化，加入硝酸银溶液acidify with dilute nitric acid, then add aqueous silver nitrate | 奶油色沉淀 AgBr，难溶于稀氨水，溶于浓氨水cream precipitate of AgBr, sparingly soluble in dilute ammonia, soluble in concentrated ammonia |
| I⁻ | 用稀硝酸酸化，加入硝酸银溶液acidify with dilute nitric acid, then add aqueous silver nitrate | 黄色沉淀 AgI，不溶于浓氨水yellow precipitate of AgI, insoluble in concentrated ammonia |
| SO₄²⁻ | 用稀盐酸或稀硝酸酸化，加入钡盐溶液acidify with dilute hydrochloric or nitric acid, then add an aqueous barium salt | 白色沉淀 BaSO₄，不溶于过量稀强酸white precipitate of BaSO₄, insoluble in excess dilute strong acid |
| SO₃²⁻ | 加入钡盐溶液，再加稀强酸add an aqueous barium salt, then dilute strong acid | 白色沉淀 BaSO₃，溶于稀强酸并放出 SO₂white precipitate of BaSO₃, which dissolves in dilute strong acid with release of SO₂ |
| NO₃⁻ | 加入氢氧化钠溶液和铝箔，加热warm with aqueous sodium hydroxide and aluminium foil | 放出 NH₃，使湿润的红色石蕊试纸变蓝NH₃ is given off, turning damp red litmus paper blue |
| NO₂⁻ | 加入氢氧化钠溶液和铝箔，加热；或加入稀酸warm with aqueous sodium hydroxide and aluminium foil; or add dilute acid | 放出 NH₃；加稀酸时生成 NO，遇空气变为红棕色 NO₂NH₃ is given off; with dilute acid, NO forms and turns red-brown (NO₂) in air |
气体的检验Tests for gases
| 气体 Gas | 操作 Test | 现象 Result |
|---|---|---|
| H₂ | 用燃着的木条靠近hold a lighted splint at the mouth of the tube | 发出轻微的爆鸣声burns with a squeaky pop |
| O₂ | 伸入带火星的木条insert a glowing splint | 木条复燃the splint relights |
| CO₂ | 通入澄清石灰水bubble through limewater | 石灰水变浑浊（生成 CaCO₃）limewater turns milky (CaCO₃ forms) |
| NH₃ | 用湿润的红色石蕊试纸检验hold damp red litmus paper in the gas | 试纸变蓝the paper turns blue |
| Cl₂ | 用湿润的蓝色石蕊试纸检验hold damp blue litmus paper in the gas | 试纸先变红后褪色the paper turns red, then is bleached |
| SO₂ | 通入酸性重铬酸钾溶液bubble through acidified potassium dichromate(VI) | 溶液由橙色变为绿色the solution turns from orange to green |
| H₂O | 接触无水硫酸铜add to anhydrous copper(II) sulfate | 白色固体变为蓝色the white solid turns blue |