Question

What is the Ka chemistry constant?

Answer 1

`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:

`HA(aq) + H_2O(l) rightleftharpoonsH_3O^+ + A^-`

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

`K_a=([H_3O^+][A^-])/([HA])`

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 `pK_a` values (`pK_a=-log_10K_a`) have been reported.