定义Definition
碱有几种定义：阿伦尼乌斯认为碱在水中电离产生 OH⁻；布朗斯特–劳里理论中碱是质子（H⁺）受体；路易斯理论中碱是电子对给体。能溶于水的碱称为可溶性碱（alkali），如 NaOH、KOH。
There are several definitions of a base: for Arrhenius, a substance releasing OH⁻ in water; in Brønsted–Lowry theory, a proton (H⁺) acceptor; in Lewis theory, an electron-pair donor. Bases that dissolve in water are alkalis, such as NaOH and KOH.
强碱与弱碱Strong and weak bases
强碱在水中完全电离，如 NaOH、KOH、Ba(OH)₂。弱碱只部分反应，如氨：NH₃ + H₂O ⇌ NH₄⁺ + OH⁻，以及胺类。金属氧化物和碳酸盐也能与酸反应，属于布朗斯特碱。碱的共轭酸越弱，碱越强。
Strong bases ionise completely in water, such as NaOH, KOH and Ba(OH)₂. Weak bases react only partly, such as ammonia, NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, and amines. Metal oxides and carbonates also react with acids and are Brønsted bases. The weaker the conjugate acid, the stronger the base.
典型反应Typical reactions
与酸中和生成盐和水；可溶性碱与铵盐共热放出氨气（检验 NH₄⁺）；与许多金属离子生成氢氧化物沉淀，如 Cu²⁺ + 2OH⁻ → Cu(OH)₂（蓝色）；强碱能与两性氧化物 Al₂O₃ 反应。碱溶液使红色石蕊试纸变蓝、酚酞变红。
Bases neutralise acids to form salts and water; alkalis heated with ammonium salts release ammonia (the test for NH₄⁺); they precipitate many metal hydroxides, e.g. Cu²⁺ + 2OH⁻ → Cu(OH)₂ (blue); strong bases react with amphoteric Al₂O₃. Alkaline solutions turn red litmus blue and phenolphthalein pink.
年表Timeline
- 1887
阿伦尼乌斯发表电离理论，以 OH⁻ 定义碱
Arrhenius publishes ionic dissociation theory, defining bases by OH⁻
- 1923
布朗斯特与劳里提出质子理论；路易斯提出电子对理论
Brønsted and Lowry propose the proton theory; Lewis proposes the electron-pair theory