Question

What species are in the buffer region of a weak acid–strong base titration? How are they different from the species at the equivalence point? How are they different from the species in the buffer region of a weak base–strong acid titration?

Short answer

The conjugate base of a weak acid $\text{HA is} {\text{A}}^{\text{-}}$. The weak acid and the strong base are used in equal proportions. The conjugate acid of a weak base and the weak base are ${\text{BH}}^{\text{+}}\text{/B}$.

Step-by-step solution

Define equivalence point

In a titration, the equivalence point is reached when the amount of titrant administered is sufficient to totally neutralise the analyte solution.

Explanation

The weak acid and its conjugate base ${\text{HA/A}}^{\text{-}}$reside in the buffer zone of a weak acid-strong base titration. When a weak acid combines with a strong base, such as $\text{NaOH}$, this is what happens.

$\text{HA + NaOH}\rightleftharpoons {\text{Na}}^{\text{+}}{\text{+H}}_{\text{2}}{\text{O +A}}^{\text{-}}$

The term "equivalent point" refers to the presence of an equal amount of weak acid and strong base. As a result, all $\text{HA}$reacts with $\text{NaOH}$. As a result, only ${\text{Na}}^{\text{+}}$and ${\text{A}}^{\text{-}}$will exist.

The weak base and its conjugate acid ${\text{BH}}^{\text{+}}\text{/B}$exist in the buffer area of a weak base-strong acid titration. When a weak base reacts with a strong acid, such as $\text{HCl}$, this is what happens.

$\text{B + HCl}\rightleftharpoons {\text{BH}}^{\text{+}}{\text{+ Cl}}^{\text{-}}$

Therefore, the conjugate base of a weak acid ${\text{HA/A}}^{\text{-}}$and the conjugate acid of a weak base ${\text{BH}}^{\text{+}}\text{/B}$.