The

**pKa**is a measure of the strength of an acid. Specifically, it's the negative log of the dissociation constant for an acid in water. There is no way to convert**pKa**to**pH**because they're not equivalent. The**pH**is a measure of acid in solution.Correspondingly, how do you go from pKa to Ka?

To create a more manageable number, chemists define the

**pKa**value as the negative logarithm of the**Ka**value:**pKa**= -log**Ka**. If you already know the**pKa**value for an acid and you need the**Ka**value, you find it by taking the antilog. In practice, this means raising both sides of the equality to exponents of 10.What is the pKa?

Therefore,

**pKa**was introduced as an index to express the acidity of weak acids, where**pKa**is defined as follows. For example, the Ka constant for acetic acid (CH_{3}COOH) is 0.0000158 (= 10^{-}^{4.8}), but the**pKa**constant is 4.8, which is a simpler expression. In addition, the smaller the**pKa**value, the stronger the acid.