定义Definition
实验式是用元素符号表示化合物中各元素原子数目最简整数比的化学式，如乙烷 C₂H₆ 的实验式为 CH₃，葡萄糖 C₆H₁₂O₆ 的实验式为 CH₂O。离子化合物的化学式就是实验式，如 NaCl、MgCl₂。
An empirical formula gives the simplest whole-number ratio of atoms of each element in a compound: CH₃ for ethane, C₂H₆, and CH₂O for glucose, C₆H₁₂O₆. The formulas of ionic compounds, such as NaCl and MgCl₂, are empirical formulas.
由组成计算Working it out
把各元素的质量（或质量分数）除以其相对原子质量得到物质的量之比，再除以其中最小的数并化为整数。例：某化合物含 Mg 60.3%、O 39.7%，Mg : O = 60.3/24.3 : 39.7/16.0 = 2.48 : 2.48 = 1 : 1，实验式为 MgO。比值接近 1.5、1.33 等时要乘以 2、3 化为整数。
Divide each element's mass (or percentage) by its relative atomic mass to get the mole ratio, divide by the smallest value and round to whole numbers. A compound with 60.3% Mg and 39.7% O gives Mg : O = 60.3/24.3 : 39.7/16.0 = 2.48 : 2.48 = 1 : 1, so MgO. Ratios near 1.5 or 1.33 must be multiplied by 2 or 3.
与分子式的关系Link to the molecular formula
分子式是实验式的整数倍：n = Mr ÷ 实验式式量。不同物质可以有相同的实验式，如乙炔 C₂H₂ 和苯 C₆H₆ 都是 CH。
The molecular formula is a whole-number multiple of the empirical formula: n = Mr ÷ empirical formula mass. Different substances can share an empirical formula; ethyne, C₂H₂, and benzene, C₆H₆, are both CH.
年表Timeline
- 1799
普鲁斯特提出定比定律，化合物组成固定
Proust states the law of definite proportions: compounds have fixed composition
- 1831
李比希完善有机物燃烧分析，可精确测定 C、H 含量
Liebig perfects combustion analysis for accurate carbon and hydrogen content