含义Meaning
难溶电解质饱和溶液中离子浓度幂之积为常数。由 Ksp 可算溶解度 s，并用离子积 Q 判断沉淀生成或溶解（能斯特，1889）。
In a saturated solution of a sparingly soluble salt the ion product is constant. Ksp gives solubility s, and comparing the ion product Q with Ksp predicts precipitation or dissolution.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(K_{sp}\) | 溶度积solubility product | 1 |
| \(s\) | 摩尔溶解度molar solubility | mol·L⁻¹ |
| \(Q\) | 离子积ion product | 1 |
推导Derivation
固体活度为 1，平衡常数只含离子浓度。
The solid has unit activity.
纯水中溶解 s mol/L：\([\mathrm M] = ms\)，\([\mathrm X] = ns\)，代入得 \(K_{sp} = m^mn^ns^{m+n}\)。
In pure water [M] = ms, [X] = ns.
不同类型的盐不能直接比较 Ksp 大小判断溶解度，需换算成 s。
Compare solubilities via s, not Ksp, across salt types.
适用条件与局限Assumptions & limitations
忽略离子强度（盐效应使溶解度增大）、水解、配位和离子对；这些因素可使实际溶解度大很多。
Ignores ionic strength, hydrolysis, complexation and ion pairing, which can raise solubility considerably.
例题Worked example
AgCl：Ksp = 1.8×10⁻¹⁰，s = 1.3×10⁻⁵ mol/L；Ag₂CrO₄：Ksp = 1.1×10⁻¹²，s = (Ksp/4)^{1/3} = 6.5×10⁻⁵ mol/L——Ksp 更小，溶解度反而更大。
AgCl s = 1.3×10⁻⁵ M; Ag₂CrO₄ (smaller Ksp) s = 6.5×10⁻⁵ M — more soluble.