# How does an acid-base buffer system function?

May 21, 2016

A buffer solution is usually made from a weak acid and its conjugate base or vice-versa. By definition a buffer solution is an aqueous solution that resists the change on its pH.

#### Explanation:

A buffer solution is usually made from a weak acid and its conjugate base or vice-versa.

By definition a buffer solution is an aqueous solution that resists the change on its pH.

Consider the buffer solution made from the weak acid $\textcolor{red}{H A}$ and the salt of its conjugate base $\textcolor{b l u e}{N a A}$.

1- When an acid $\textcolor{\mathrm{da} r k red}{{H}^{+}}$ is added to the solution, it will react with the conjugate acid $\textcolor{b l u e}{{A}^{-}}$ to form the weak acid $\textcolor{red}{H A}$ according to the following reaction:

$\textcolor{\mathrm{da} r k red}{{H}^{+}} + \textcolor{b l u e}{{A}^{-}} \to \textcolor{red}{H A}$

Therefore, the $\left[\textcolor{\mathrm{da} r k red}{{H}^{+}}\right]$ in the solution will not change dramatically and the pH will remain almost unchanged.

2- When a base $\textcolor{\mathrm{da} r k b l u e}{O {H}^{-}}$ is added to the solution, it will react with the acid $\textcolor{red}{H A}$ to form the conjugate base $\textcolor{b l u e}{{A}^{-}}$ and water according to the following reaction:

$\textcolor{\mathrm{da} r k b l u e}{O {H}^{-}} + \textcolor{red}{H A} \to \textcolor{b l u e}{{A}^{-}} + \textcolor{g r e e n}{{H}_{2} O}$

Therefore, the $\left[\textcolor{\mathrm{da} r k red}{{H}^{+}}\right]$ in the solution will not change dramatically and the pH will remain almost unchanged.

Note that, the amount of acid and base that we can add to the solution before the pH starts to change dramatically depends on the buffer capacity of the solution.

In order to fully understand this topic formats all aspects, I would recommend the following video:

Acid - Base Equilibria | Buffer Solution.