A base is a substance that dissociates or ionises in water to form hydroxide ions (OH⁻); their presence gives a basic (alkaline) solution its characteristic properties, such as a pH above 7 and the ability to neutralise acids. Sodium hydroxide and aqueous ammonia are common examples. [Ch.12 extension: beyond the Arrhenius (OH⁻ in water) sense, a base is also a Brønsted proton acceptor and a Lewis electron-pair donor.]

碱是在水中解离或电离生成氢氧根离子(OH⁻)的物质;这些氢氧根离子的存在使碱性溶液具有特征性质,如 pH 高于 7 以及能中和酸。氢氧化钠和氨水是常见的例子。【第12章扩展:除阿伦尼乌斯(水中给 OH⁻)定义外,碱还可定义为布朗斯特质子受体和路易斯电子对给体。】