Question

You have a solution of the weak acid HA and add some of the salt NaA to it. What are the major species in the solution? What do you need to know to calculate the pH of the solution, and how would you use this information? How does the pH of the solution of just the HA compare with that of the final mixture? Explain.

Short answer

When a strong acid is added to a solution of a weak acid, $\text{HCl}$would completely ionize while the weak acid would partially ionize.

To calculate the $\text{pH}$of the solution, the concentration of the solution that was added along with$\text{Ka}$ value of the weak acid.

The $\text{pH}$of the$\text{HA}$ solution will be higher than$\text{pH}$ of the final mixture since $\text{HCl}$completely dissociates in the solution whereas the weak acid dissociates only partially.

Step-by-step solution

Definition of pH

The $\text{pH}$is used to evaluate the acidity or basicity of aqueous or other liquid solutions.

Explanations

When a strong acid is added to a solution of weak acid, $\mathbf{\text{HCl}}$would completely ionize while the weak acid would partially ionize. The presence of hydrogen ions from the ionization of$\text{HCl}$ would prevent or subdue the ionization of the weak acid$\text{HA}$ by the common ion effect. It means there would largely be$\left[{\text{H}}^{\text{+}}\right]\text{,}\left[{\text{Cl}}^{\text{-}}\right]\text{,\hspace{0.17em}and\hspace{0.17em}}\left[\text{HA}\right]$ in solution.

To calculate the $\mathbf{\text{pH}}$of the solution, the concentration of the solution that was added along with$\mathbf{\text{Ka}}$ value of the weak acid. This data helps to calculate the moles of ${\text{H}}^{\text{+}}$from$\text{HCl}$ along with the moles of${\mathbf{\text{H}}}^{\mathbf{\text{+}}}$ from$\text{HA}$.

The $\mathbf{\text{pH}}$of the$\mathbf{\text{HA}}$ solution will be higher thanrole="math" localid="1657716046018" $\mathbf{\text{pH}}$ of the final mixture since role="math" localid="1657715710454" $\mathbf{\text{HCl}}$completely dissociates in the solution whereas the weak acid dissociates only partially.