\[b_\mathrm{B} = \frac{n_\mathrm{B}}{m_\mathrm{A}}\]
与物质的量浓度换算（ρ 用 g/mL）conversion from molarity (ρ in g/mL)
\[b = \frac{1000\,c}{1000\rho - cM_\mathrm{B}}\]含义Meaning
每千克溶剂中溶质的物质的量，单位 mol/kg。不随温度变化，是依数性公式所用的浓度。
Amount of solute per kilogram of solvent (mol/kg). Temperature-independent; used in colligative-property formulas.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(b_\mathrm{B}\) | 溶质 B 的质量摩尔浓度molality of B | mol·kg⁻¹ |
| \(m_\mathrm{A}\) | 溶剂质量mass of solvent | kg |
推导Derivation
按定义；分母是溶剂而非溶液的质量。
By definition; the denominator is the solvent mass, not the solution’s.
1 L 溶液质量 \(1000\rho\) g，含溶质 \(c\) mol 即 \(cM_\mathrm{B}\) g，溶剂质量 \((1000\rho - cM_\mathrm{B})\) g，得换算式。
1 L of solution weighs \(1000\rho\) g, of which \(cM_\mathrm{B}\) g is solute; the rest is solvent.
适用条件与局限Assumptions & limitations
稀水溶液中 \(b \approx c\)（数值上，mol/kg ≈ mol/L）。
In dilute aqueous solution \(b \approx c\) numerically.