Principles of Ionization of Weak Acids

The Fundamental Concept of Buffers is that

A Buffer Resists Change

pH buffers resist change in pH when either acid (H+) or base (OH-) is added to it.

Chemicals which are pH buffers are weak acids or bases

Acids= Proton (H+) donors

Bases= Proton Acceptors

{*Figure 1*}

Acids and their conjugate bases are in equilibrium

since equilibria are related to the properties of the reactants and products,

so for weak acids, the tendency to give up its proton determines its buffering property.

This tendency to ionize can be put in terms of an equation for the equilibrium:

{*Figure 2*}

Where [ ] = Molar concentration

K = Ionization constant

Simplest example is water (H2O)

{*Figure 3*}

But since [H2O] (water concentration) = Constant (55.5 M)

Kw = [H+][OH-] = 10^-14 M

In pure water, [H+] = [OH-] = 10^-7 M

To make this easier to use, the pH scale was invented.

pH = -log [H+]

thus [H+] = 10^-7 M

pH = 7

This is called Neutral pH because it is in the middle of the pH scale.

At pH greater than neutral, the solution is alkaline

while at pH less than neutral, the solution is acid.

{*Figure 4*}