pH and pKa · pH与pKa
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| pKa/piː kɑː/ | 酸度系数 | suān dù xì shù |
A number for acid strength
- Comparing tiny $K_a$ values full of exponents is awkward.
- A logarithm turns each into a friendly small number.
- Now stronger acids get lower scores.
- One glance ranks any list of acids.
一个表示酸强度的数
- 比较满是指数的微小 $K_a$ 值很别扭。
- 对数把每一个变成一个友好的小数。
- 现在更强的酸得到更低的分数。
- 看一眼就能给任何一列酸排名。
Defining pKa
- pKa 酸度系数 measures acid strength: $\text{p}K_a = -\log K_a$.
- A smaller $\text{p}K_a$ means a stronger acid.
- It compresses the huge range of $K_a$ values.
定义 pKa
- 酸度系数衡量酸的强度:$\text{p}K_a = -\log K_a$。
- 更小的 $\text{p}K_a$ 意味着更强的酸。
- 它把 $K_a$ 值的巨大范围压缩。
$\text{p}K_a$ is defined as... · $\text{p}K_a$定义为...
$\text{p}K_a = -\log K_a$.
Lower pKa, stronger acid
- Because of the negative log, a big $K_a$ gives a small $\text{p}K_a$.
- So the strongest acids have the lowest $\text{p}K_a$.
- Rank acids by lining up their $\text{p}K_a$ values.
pKa 越低,酸越强
- 由于负对数,大的 $K_a$ 给出小的 $\text{p}K_a$。
- 所以最强的酸有最低的 $\text{p}K_a$。
- 把各酸的 $\text{p}K_a$ 值排开来给它们排名。
Which acid is stronger? · 哪种酸更强？
A lower $\text{p}K_a$ means a stronger acid. · 较低的$\text{p}K_a$意味着更强的酸。
A larger $K_a$ corresponds to a smaller $\text{p}K_a$. · 较大的$K_a$对应较小的$\text{p}K_a$。
The negative log inverts the order. · 负对数反转了顺序。
Comparing pKa to pH
- If a solution's pH is below the acid's $\text{p}K_a$, the acid form dominates.
- If pH is above $\text{p}K_a$, the base form dominates.
- They are present equally when pH equals $\text{p}K_a$.
把 pKa 与 pH 比较
- 若溶液的 pH 低于酸的 $\text{p}K_a$,酸的形式占主导。
- 若 pH 高于 $\text{p}K_a$,碱的形式占主导。
- 当 pH 等于 $\text{p}K_a$ 时,两者等量存在。
Read strength from pKa · 从pKa读取强度
Sort each acid by its pKa. A smaller pKa means a stronger acid. · 按pKa对每种酸排序。较小的pKa意味着更强的酸。
When a solution's pH equals the acid's $\text{p}K_a$, the acid and conjugate base are... · 当溶液的pH等于酸的$\text{p}K_a$时，酸和共轭碱……
At $\text{pH} = \text{p}K_a$, the two forms are equal. · 在$\text{pH} = \text{p}K_a$处，两种形式相等。
When pH is below $\text{p}K_a$, the ____ form of the species dominates. · 当pH低于$\text{p}K_a$时，物种的____形式占主导。
A more acidic solution favours the protonated (acid) form. · 酸性更强的溶液有利于质子化（酸）形式。
Acid A has $\text{p}K_a = 3$; acid B has $\text{p}K_a = 5$. Which is stronger?
- A lower $\text{p}K_a$ means a stronger acid.
- So acid A ($\text{p}K_a = 3$) is the stronger acid.
酸 A 的 $\text{p}K_a = 3$;酸 B 的 $\text{p}K_a = 5$。哪个更强?
- 更低的 $\text{p}K_a$ 意味着更强的酸。
- 所以酸 A($\text{p}K_a = 3$)是更强的酸。
$\text{p}K_a$ is a fixed property of the acid, while pH depends on the solution. · $\text{p}K_a$是酸的固有属性，而pH取决于溶液。
$\text{p}K_a$ describes the acid; pH describes the mixture. · $\text{p}K_a$描述酸；pH描述混合物。
A smaller $\text{p}K_a$ is a stronger acid -- the negative log flips the order, a common mix-up. $\text{p}K_a$ is a property of the acid; pH is a property of the solution. And when $\text{pH} = \text{p}K_a$, the acid and its conjugate base are present in equal amounts.
更小的 $\text{p}K_a$ 是更强的酸——负对数把顺序反过来,这是常见的混淆。$\text{p}K_a$ 是酸的性质;pH 是溶液的性质。而且当 $\text{pH} = \text{p}K_a$ 时,酸和它的共轭碱等量存在。
pKa $= -\log K_a$ ranks acid strength on a friendly scale: a smaller $\text{p}K_a$ is a stronger acid. Comparing it to a solution's pH tells you which form dominates -- the acid form below $\text{p}K_a$, the base form above, and equal amounts when $\text{pH} = \text{p}K_a$.
酸度系数 $= -\log K_a$ 在一个友好的标度上给酸的强度排名:更小的 $\text{p}K_a$ 是更强的酸。把它与溶液的 pH 比较,能知道哪种形式占主导——$\text{p}K_a$ 以下酸的形式占主导,以上碱的形式占主导,$\text{pH} = \text{p}K_a$ 时等量。