# How does pH change during titration?

Oct 6, 2015

It depends.

#### Explanation:

If we consider the titration of an acid by a base, the pH will increase. However, if we titrate a base by an acid, the pH will decrease.

Example:
Let us consider the titration of $1 M$ $H C l$ by $1 M$ $N a O H$.
The initial pH of the acidic solution $H C l \left(a q\right)$ is around $1$. This is resulting from the high concentration of $\left[{H}^{+}\right]$.

When $N a O H$ is added to the solution, the $O {H}^{-}$ ions from $N a O H$ will react with the ${H}^{+}$ ions from $H C l$ to form water ${H}_{2} O$ according to the following reaction:

${H}^{+} + O {H}^{-} \to {H}_{2} O$

Since the $\left[{H}^{+}\right]$ is decreasing and knowing that the $p H = - \log \left[{H}^{+}\right]$ the $p H$ will increase until neutralization where the $p H = 7$. If we continue adding $N a O H$ the $p H$ will continue increasing until reaching a maximum value of $p H = 14$.

Here is a video explaining titration of an acid by a base, including the stoichiometry.