# What is the Ka chemistry constant?

Dec 9, 2016

${K}_{a}$ is the acid dissociation constant that has been measured for many different acids.

#### Explanation:

In aqueous solution, an acid dissociates according to the following reaction:

$H A \left(a q\right) + {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {A}^{-}$

We can usually measure the extent of this equilibrium by some some means, and thus:

${K}_{a} = \frac{\left[{H}_{3} {O}^{+}\right] \left[{A}^{-}\right]}{\left[H A\right]}$

Here, ${K}_{a}$ is a numerical constant that might be large or small. Strong mineral acids such as HX, X=Cl, Br, I; H_2SO_4; HClO_4, have very large acid dissociation constants, and the equilibrium lies strongly to the right. For weaker acids the equilibrium lies to the LEFT. In your text you will probably find a list of weak acids, whose $p {K}_{a}$ values ($p {K}_{a} = - {\log}_{10} {K}_{a}$) have been reported.