浓度换算与配液Concentration & solution prep
所有计算都在你的浏览器里完成。ppm / ppb 必须先明确基准，并显示所用的密度假设。 Everything is calculated in your browser. For ppm / ppb you must choose the basis, and the density assumption is shown.
公式与适用条件Formulas and conditions
- 符号：cm 质量浓度（g/L），cn 摩尔浓度（mol/L），M 溶质摩尔质量（g/mol），F 比例（无量纲，ppm = 10⁻⁶，ppb = 10⁻⁹）。
- Symbols: cm mass concentration (g/L), cn molar concentration (mol/L), M solute molar mass (g/mol), F fraction (dimensionless; ppm = 10⁻⁶, ppb = 10⁻⁹).
- cn = cm / M 质量 ↔ 摩尔，需要摩尔质量（kDa = 1000 g/mol，Da = 1 g/mol）。mass ↔ molar; needs the molar mass (kDa = 1000 g/mol, Da = 1 g/mol).
- cm = F · ρsol 质量比 w/w：ρsol 是溶液密度（g/mL × 1000 = g/L）。只有 ρsol = 1.000 g/mL 时才有 1 ppm ≈ 1 µg/mL。mass ratio w/w: ρsol is the solution density (g/mL × 1000 = g/L). 1 ppm ≈ 1 µg/mL holds only when ρsol = 1.000 g/mL.
- cm = F · ρsolute 体积比 v/v：ρsolute 是纯溶质的密度（没有默认值）；假设混合时体积可加。volume ratio v/v: ρsolute is the density of the pure solute (no default); volumes are assumed additive.
- cn = F · ρsol / Msolvent 摩尔比 n/n：稀溶液近似（n总 ≈ n溶剂）。mole ratio n/n: dilute-solution approximation (ntotal ≈ nsolvent).
- ppm ↔ ppb 直接乘以 10³，与基准和密度无关。同类单位之间只是十进制因子。ppm ↔ ppb is a plain factor of 10³, independent of basis and density. Units of the same kind differ only by decimal factors.
- C1V1 = C2V2 稀释；加入溶剂体积 = V2 − V1（体积可加）；稀释倍数 = C1/C2。必须 C1 ≥ C2。不允许 ppm/ppb（先在“浓度换算”里换成质量或摩尔浓度）。dilution; solvent added = V2 − V1 (additive volumes); dilution factor = C1/C2. Requires C1 ≥ C2. ppm/ppb are not allowed here (convert to mass or molar concentration first).
- m = cm·V 或 m = cn·V·M，mweigh = m / (purity/100) 配储备液：把该质量的溶质溶于溶剂，定容到总体积 V（不是加入体积 V 的溶剂）。M 要用实际称取形态（含结晶水时用水合物）的摩尔质量；请自行确认不超过溶解度。stock solution: dissolve that mass and make up to the final volume V (not “add volume V of solvent”). Use the molar mass of the form actually weighed (hydrate if applicable); check solubility yourself.
- 适用范围：稀溶液（溶质质量分数 ≲ 1%）。不适用：气体中的 ppm（见“气体 ppm 与 mg/m³”）；活度、解离、温度对密度的影响（密度由你给定）。Scope: dilute solutions (solute mass fraction ≲ 1%). Not covered: ppm in gases, activities, dissociation, temperature dependence of density (you supply the density).
显示位数只是格式，结果准确度受输入精度和所用假设限制；本工具不做不确定度传递。Displayed digits are only formatting; accuracy is limited by your inputs and the assumptions used. No uncertainty propagation is done.
使用的常数Constants used
本工具不使用物理常数：只用精确的十进制前缀因子（k=10³、m=10⁻³、µ=10⁻⁶、n=10⁻⁹、p=10⁻¹²）。水的密度、水的摩尔质量等是下面的“假设”，不是常数。This tool uses no physical constants, only exact decimal prefix factors (k=10³, m=10⁻³, µ=10⁻⁶, n=10⁻⁹, p=10⁻¹²). The density of water, the molar mass of water, etc. are the “assumptions” below, not constants.
ppm / ppb 的基准（必须明确选择，没有默认）Basis of ppm / ppb (you must choose; no default)
预设值是教科书值，不是 SI 常数，请核对你的实际溶液。Presets are textbook values, not SI constants; check them against your actual solution.
被求的那一项的输入框会被忽略，只用它旁边的单位选择结果的单位。C₁ 和 C₂ 必须同类（都是质量浓度或都是摩尔浓度）。The input box of the unknown is ignored; only its unit selector is used for the result. C₁ and C₂ must be of the same kind (both mass or both molar).