\[i = 1 + \alpha(\nu - 1)\]
缔合（m 个分子结合为一个）association of m molecules into one
\[i = 1 - \beta\left(1 - \frac{1}{m}\right)\]含义Meaning
溶液中实际粒子数与溶解的化学式单元数之比。决定电解质依数性的放大倍数。
Ratio of particles actually present to formula units dissolved — the multiplier for colligative properties of electrolytes.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(\alpha\) | 电离度degree of dissociation | 1 |
| \(\nu\) | 每个化学式电离出的离子数ions per formula unit | 1 |
| \(\beta\) | 缔合度degree of association | 1 |
推导Derivation
1 mol 溶质中 α mol 电离，生成 \(\alpha\nu\) mol 离子，剩余 \(1-\alpha\) mol 分子。
Of 1 mol solute, α mol dissociates into \(\alpha\nu\) mol ions, leaving \(1-\alpha\) mol.
粒子总数 \(1 - \alpha + \alpha\nu = 1 + \alpha(\nu-1)\)。
Total particles: \(1 + \alpha(\nu-1)\).
由依数性测得 i，可反求弱电解质的电离度 \(\alpha = (i-1)/(\nu-1)\)。
Measuring i colligatively gives \(\alpha = (i-1)/(\nu-1)\).
适用条件与局限Assumptions & limitations
强电解质并不是“未完全电离”，i < ν 主要由离子间作用（活度系数）造成。
For strong electrolytes i < ν reflects ion–ion interactions (activity), not incomplete dissociation.
羧酸在苯中二聚，i ≈ 0.5。
Carboxylic acids dimerise in benzene, i ≈ 0.5.