定义Definition
强酸是在水溶液中几乎完全电离的酸，如盐酸 HCl、氢溴酸 HBr、氢碘酸 HI、硝酸 HNO₃、高氯酸 HClO₄ 和硫酸 H₂SO₄（第一步电离）。强酸的 pKa 通常小于 0。
A strong acid ionises almost completely in water, such as hydrochloric HCl, hydrobromic HBr, hydriodic HI, nitric HNO₃, perchloric HClO₄ and sulfuric H₂SO₄ (first ionisation). Strong acids usually have pKa below 0.
pH 计算Calculating pH
一元强酸完全电离，[H⁺] = c，pH = −lg c。例：0.010 mol dm⁻³ HCl 的 pH = 2.00；稀释 10 倍 pH 增大 1。0.050 mol dm⁻³ H₂SO₄ 若按两步完全电离近似，[H⁺] = 0.10 mol dm⁻³，pH ≈ 1.0。
A monoprotic strong acid is fully ionised, so [H⁺] = c and pH = −log c. 0.010 mol dm⁻³ HCl has pH 2.00, and each tenfold dilution raises the pH by 1. Treating 0.050 mol dm⁻³ H₂SO₄ as fully ionised in both steps gives [H⁺] = 0.10 mol dm⁻³, pH ≈ 1.0.
拉平效应The levelling effect
在水中，比 H₃O⁺ 更强的酸都把质子完全交给水，因此 HCl、HBr、HI、HClO₄ 在水中显得一样强，水中能存在的最强酸是 H₃O⁺。在冰乙酸等酸性较弱的溶剂中，可以区分它们的相对强弱：HClO₄ > HI > HBr > HCl。
In water every acid stronger than H₃O⁺ hands its proton completely to water, so HCl, HBr, HI and HClO₄ all appear equally strong; the strongest acid that can exist in water is H₃O⁺. In a less basic solvent such as glacial ethanoic acid they can be ranked: HClO₄ > HI > HBr > HCl.
年表Timeline
- 1887
阿伦尼乌斯提出强电解质在水中完全电离
Arrhenius proposes that strong electrolytes ionise completely
- 1923
德拜与休克尔提出强电解质溶液理论
Debye and Hückel propose their theory of strong electrolyte solutions