3.1 Review of Acids and Bases and Ka
3.1 酸碱和Ka的回顾

The most commonly applied definition of acids and bases is the Brønsted-Lowry definition:
最常用的酸和碱定义是 Brønsted-Lowry 定义：

• Brønsted-Lowry Acid: a substance that can donate a proton (H+)
  Brønsted-Lowry Acid：一种可以提供质子的物质（H + ）

• Brønsted-Lowry Base: a substance that can accept a proton (H+)
  Brønsted-Lowry 碱：可以接受质子的物质 (H + )

Therefore, according to the Brønsted-Lowry definition, an acid-base reaction is a proton transfer process in which the acid gives away a proton and the base accepts a proton as shown in the general equation:
因此，根据 Brønsted-Lowry 定义，酸碱反应是一个质子转移过程，其中酸放出质子，碱接受质子，如通式所示：

General equation for acid-base reaction
酸碱反应的一般方程

The species that forms when an acid loses its proton is called the conjugate base of that acid; similarly, the species that forms when a base accepts a proton is called the conjugate acid of that base. In the general equation above, HA is the conjugate acid of A–, and A– is the conjugate base of HA. HA and A– can also be called a conjugate acid-base pair; another pair is HB+ and B.
当酸失去质子时形成的物质称为该酸的共轭碱；同样，当碱接受质子时形成的物质称为该碱的共轭酸。在上面的通式中，HA是A – 的共轭酸，A – 是HA的共轭碱。 HA和A – 也可称为共轭酸碱对；另一对是 HB + 和 B。

A strong acid donates the proton completely, and the arrow “→” can be used in the reaction equation to indicate that the reaction goes to completion. The dissociation reaction of the strong acid HCl in water is used as an example here:
强酸完全给出质子，反应方程式中可用箭头“→”表示反应完全。这里以强酸性HCl在水中的解离反应为例：

HCl (g) + H2O (l) →H3O+(aq) + Cl–(aq)

For weak acids (HA is used as a general formula), the proton is only partially donated and the reaction stays at equilibrium. The equilibrium arrow “” will be needed in the reaction equation to indicate the equilibrium status:
对于弱酸（HA用作通式），仅提供部分质子，反应保持平衡。反应方程中需要平衡箭头“ ”来指示平衡状态：

HA (aq) + H2O (l) ⇔ H3O+ (aq) + A– (aq)

The equilibrium constant for the above reaction is called the acid dissociation constant, Ka. It is a constant to measure the relative strength of an acid. The expression for Ka is:
上述反应的平衡常数称为酸解离常数，K a. 它是衡量酸相对强度的常数。 K a 的表达式为：

The larger the Ka value, the stronger the ability of the acid to donate protons, and the stronger the acid is. (Technically, when the Ka value is larger than 10, the acid can be regarded as a strong acid.)
K a 值越大，酸贡献质子的能力越强，酸越强。 （从技术上讲，当K a 值大于10时，酸可以被视为强酸。）

For the conjugate acid-base pair, the stronger the acid, the weaker the conjugate base is, and vice versa.
对于共轭酸碱对来说，酸越强，共轭碱越弱，反之亦然。