A 0.15 M HNO2 aqueous solution is mixed with a 0.20 M NaNO2 aqueous solution, where the pKa of H

step 1 If we know the concentrations of the weak acid and its conjugate base in a buffer solution, and

A 0.15 M HNO2 aqueous solution is mixed with a 0.20 M NaNO2...

A $0.15 M \mathrm{HNO}_{2}$ aqueous solution is mixed with a $0.20 M \mathrm{NaNO}_{2}$ aqueous solution, where the $\mathrm{pK}_{\mathrm{a}}$ of $\mathrm{HNO}_{2}$ is equal to 3.37 . What is the $\mathrm{pH}$ of the resulting solution?

Key Concepts

Buffer Solutions

A buffer solution is formed by mixing a weak acid with its conjugate base, or a weak base with its conjugate acid. Such solutions resist significant changes in pH when small amounts of strong acids or bases are added. The buffering action results from the equilibrium between the weak acid and its conjugate base, which allows the system to neutralize added H+ or OH? ions.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a useful tool for calculating the pH of buffer solutions. It relates the pH of the solution to the pKa of the weak acid and the ratio of the concentrations of the conjugate base to the acid. The equation, pH = pKa + log([Base]/[Acid]), simplifies the estimation of pH in systems where the acid and its conjugate base are present in known amounts.

Acid-Base Equilibrium

Acid-base equilibrium is the balanced state achieved when a weak acid partially dissociates into a proton (H+) and its conjugate base, with the forward and reverse reactions occurring at equal rates. This concept is key to understanding buffer systems, as it explains how the system can adjust to maintain a stable pH when subjected to perturbations.

Acid Dissociation Constant (Ka) and pKa

The acid dissociation constant, Ka, quantifies the strength of a weak acid by describing its tendency to lose a proton in solution. The pKa, defined as the negative logarithm of Ka, provides a more convenient way to express this value and indicates the pH at which the acid is half dissociated. These parameters are critical for predicting the behavior of acid-base equilibria and for applying the Henderson-Hasselbalch equation effectively in buffer calculations.

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