Q19.45P - Chemistry: Molecular Nature Of Matter And Change

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?

Step-by-Step Solution

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 1: 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.

Step 2: 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 ${\text{BH}}^{\text{ + }}\text{/B}$.