Chapter 10, Problem 10.81AP

Interpretation Introduction

Interpretation:

The moles of sodium hydroxide needed for addition to 1 liter solution of given buffer system to reach $pH$ at 9.25 should be determined.

Concept Introduction:

Henderson-Hasselbalch equation

$\text{pKa}\text{=}\text{pH}\text{+}\text{log}\frac{\left[\text{HA}\right]}{\left[{\text{A}}^{\text{-}}\right]}$

Henderson-Hasselbalch equation explains the relationship between $pH$ of solution and $p{K}_a$ of acid. For a dissociation of acid $\left(HA\right)$ in aqueous solution,

$\text{HA}\text{+}{\text{H}}_{\text{2}}\text{O}\underset{}{\overset{}{\rightleftharpoons }}{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\text{+}{\text{A}}^{\text{-}}$

$p{K}_a=pH+\log \frac{\left[HA\right]}{\left[A^{-}\right]}$

During a dissociation of acid in aqueous solution,

• If $pH=p{K}_a$, the concentration of compound in its acidic and basic form is equal.
• If $pH<p{K}_a$, the compound exist in its acidic form.
• If $pH>p{K}_a$, the compound exist in its basic form.

According to the explanations by Lewis, if a species donates an electron pair then it is a base whereas if a species receives an electron pair, then it is acid.

When acid and base reacts, a new bond is formed between them by the lone pair of electrons.