Elemental Composition of Pure Substances · 纯净物的元素组成
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| percent composition/pəˈsent ˌkɒmpəˈzɪʃn/ | 百分组成 | bǎi fēn zǔ chéng |
| empirical formula/emˈpɪrɪkl ˈfɔːmjʊlə/ | 实验式 | shí yàn shì |
| molecular formula/məˈlekjʊlə ˈfɔːmjʊlə/ | 分子式 | fēn zǐ shì |
What is it made of?
- Break any compound down and you find fixed proportions by mass.
- Water is always 11% hydrogen and 89% oxygen by weight.
- Those percentages never change, no matter the sample size.
- From the percentages you can rebuild the formula.
它由什么组成?
- 把任何化合物分解,你都会发现按质量固定的比例。
- 水按重量总是 11% 的氢和 89% 的氧。
- 无论样品多大,这些百分比都不变。
- 从这些百分比,你可以还原出化学式。
Percent by mass
- The percent composition 百分组成 is each element's share of the total mass:
- For a formula, work it out from one mole and the molar masses.
质量百分比
- 百分组成是每种元素占总质量的份额:
- 对一个化学式,用一摩尔和各摩尔质量算出来。
In water ($\text{H}_2\text{O}$, molar mass 18), what percent of the mass is oxygen (16)? (to nearest whole %) · 在水（$\text{H}_2\text{O}$，摩尔质量 18）中，氧（16）的质量百分比是多少？（取最接近的整数%）
$16/18 \times 100 \approx 89\%$.
The empirical formula
- The empirical formula 实验式 is the simplest whole-number ratio of atoms.
- Convert each element's mass to moles, then divide by the smallest.
- Glucose has the empirical formula $\text{CH}_2\text{O}$.
实验式
- 实验式是原子数目最简单的整数比。
- 把每种元素的质量化成摩尔,再除以最小的那个。
- 葡萄糖的实验式是 $\text{CH}_2\text{O}$。
The empirical formula of a compound gives... · 化合物的实验式给出……
Empirical = simplest ratio; the molecular formula gives the actual counts. · 实验式 = 最简比；分子式给出实际的数量。
From empirical to molecular
- The molecular formula 分子式 is a whole-number multiple of the empirical one.
- Divide the true molar mass by the empirical mass to get that multiple $n$.
- Glucose: empirical $\text{CH}_2\text{O}$ ($30$), molecular $\text{C}_6\text{H}_{12}\text{O}_6$ ($180$), so $n = 6$.
从实验式到分子式
- 分子式是实验式的整数倍。
- 用真实摩尔质量除以实验式质量得到这个倍数 $n$。
- 葡萄糖:实验式 $\text{CH}_2\text{O}$($30$),分子式 $\text{C}_6\text{H}_{12}\text{O}_6$($180$),所以 $n = 6$。
A compound has empirical mass 30 and molar mass 90. The multiple $n$ for its molecular formula? · 某化合物的实验式质量为 30，分子式为 90。其分子式的倍数$n$是多少？
$n = 90/30 = 3$.
The molecular formula is always a whole-number multiple of the empirical formula. · 分子式总是实验式的整数倍。
By definition, molecular = empirical × n for some whole number n. · 根据定义，分子式 = 实验式 × n，其中 n 为某个整数。
A compound is 40% C, 6.7% H, and 53.3% O by mass. Find its empirical formula.
- Moles per 100 g: C $= 40/12 = 3.33$, H $= 6.7/1 = 6.7$, O $= 53.3/16 = 3.33$.
- Divide by the smallest ($3.33$): C 1, H 2, O 1, giving $\text{CH}_2\text{O}$.
某化合物按质量为 40% 的 C、6.7% 的 H、53.3% 的 O。求它的实验式。
- 每 100 g 的摩尔数:C $= 40/12 = 3.33$,H $= 6.7/1 = 6.7$,O $= 53.3/16 = 3.33$。
- 除以最小的($3.33$):C 1、H 2、O 1,得到 $\text{CH}_2\text{O}$。
Percent composition to formula · 百分组成转化学式
Turn a compound's percent composition into its empirical formula, step by step. · 逐步将一个化合物的百分组成转换为其实验式。
Order the steps to find an empirical formula from mass percents. · 按顺序排列从质量百分数求实验式的步骤。
Grams → moles → divide by smallest → whole-number ratio. · 克 → 摩尔 → 除以最小值 → 整数比。
After dividing by the smallest, you get a ratio of 1:1.5. You should... · 除以最小值后，你得到的比例是 1:1.5。你应该……
A .5 is real -- scale up to clear it, giving whole numbers 2:3. · .5 是真实存在的——放大以消除它，得到整数 2:3。
Percent composition gives the empirical formula, not always the molecular one -- you need the molar mass to find the multiple. When dividing moles by the smallest, round only near-whole results ($3.98 \to 4$); a stubborn $.5$ means multiply everything (by 2), never round it away. Start from a $100\ \text{g}$ sample so percentages become grams directly.
百分组成给出的是实验式,不一定是分子式——你需要摩尔质量来求倍数。用摩尔数除以最小值时,只对接近整数的结果取整($3.98 \to 4$);顽固的 $.5$ 意味着把所有数都乘(乘 2),绝不能把它取整抹掉。从 $100\ \text{g}$ 样品出发,百分数就直接变成克。
Percent composition is each element's fraction of the total mass. Turn those masses into moles and divide by the smallest to get the empirical formula (simplest ratio). The molecular formula is that empirical unit times $n$, where $n$ is the true molar mass divided by the empirical mass.
百分组成是每种元素占总质量的分数。把这些质量化成摩尔并除以最小值,得到实验式(最简比)。分子式是该实验式单元的 $n$ 倍,其中 $n$ 等于真实摩尔质量除以实验式质量。