Questions: Multiple Select Question Select all that apply Which of the following options correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base? Select all that apply. At the equivalence point, [A-] = (initial moles of HA) / (total volume). Before the equivalence point, pH is calculated by considering the unreacted weak acid only. At the equivalence point, the pH calculation is based on the reaction of the conjugate base A- with H2O. After the equivalence point, the pH depends on the concentration of the conjugate base A-. The initial [H3O+] is calculated from [HA] int and Ka.

Multiple Select Question

Select all that apply

Which of the following options correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base? Select all that apply.
At the equivalence point, [A-] = (initial moles of HA) / (total volume).
Before the equivalence point, pH is calculated by considering the unreacted weak acid only.
At the equivalence point, the pH calculation is based on the reaction of the conjugate base A- with H2O.
After the equivalence point, the pH depends on the concentration of the conjugate base A-.
The initial [H3O+] is calculated from [HA] int and Ka.

Transcript text: Multiple Select Question Select all that apply Which of the following options correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base? Select all that apply. At the equivalence point, $\left[A^{-}\right]=\frac{\text { initial moles of } H A}{\text { total volume }}$. Before the equivalence point, pH is calculated by considering the unreacted weak acid only. At the equivalence point, the pH calculation is based on the reaction of the conjugate base $\mathrm{A}^{-}$with $\mathrm{H}_{2} \mathrm{O}$. After the equivalence point, the pH depends on the concentration of the conjugate base $\mathrm{A}^{-}$. The initial $\left[\mathrm{H}_{3} \mathrm{O}^{\dagger}\right]$ is calculated from $[\mathrm{HA}]$ int and $K_{\mathrm{a}}$.

Solution

Solution Steps

Step 1: Understanding the Titration Process

In a titration of a weak acid with a strong base, the pH changes at different stages: before the equivalence point, at the equivalence point, and after the equivalence point. Each stage requires a different approach to calculate the pH.

Step 2: Analyzing Each Option

At the equivalence point, $[A^{-}]=\frac{\text{initial moles of } HA}{\text{total volume}}$.
- At the equivalence point, all the weak acid $HA$ has been converted to its conjugate base $A^-$. The concentration of $A^-$ is indeed calculated by dividing the initial moles of $HA$ by the total volume of the solution.
Before the equivalence point, pH is calculated by considering the unreacted weak acid only.
- Before the equivalence point, the solution contains both the unreacted weak acid $HA$ and its conjugate base $A^-$. The pH is typically calculated using the Henderson-Hasselbalch equation, which considers both species.
At the equivalence point, the pH calculation is based on the reaction of the conjugate base $A^-$ with $H_2O$.
- At the equivalence point, the solution contains only the conjugate base $A^-$, which reacts with water to form $OH^-$ and $HA$. The pH is determined by this hydrolysis reaction.
After the equivalence point, the pH depends on the concentration of the conjugate base $A^-$.
- After the equivalence point, the pH is primarily determined by the excess strong base added, not the conjugate base $A^-$.
The initial $[\mathrm{H}_3\mathrm{O}^+]$ is calculated from $[\mathrm{HA}]_{\text{int}}$ and $K_a$.
- The initial hydronium ion concentration $[\mathrm{H}_3\mathrm{O}^+]$ is calculated using the initial concentration of the weak acid $[\mathrm{HA}]_{\text{int}}$ and its acid dissociation constant $K_a$.

Final Answer

$\boxed{\text{At the equivalence point, } [A^{-}]=\frac{\text{initial moles of } HA}{\text{total volume}}.}$
$\boxed{\text{At the equivalence point, the pH calculation is based on the reaction of the conjugate base } A^{-} \text{ with } H_2O.}$
$\boxed{\text{The initial } [\mathrm{H}_3\mathrm{O}^+] \text{ is calculated from } [\mathrm{HA}]_{\text{int}} \text{ and } K_a.}$

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