Lactic acid (CH3 CHOHCO2 H) is found in sour milk, in sauerkraut, and in muscles after activity.

step 1 For this particular question, we can also calculate the pH using the Henderson -Hasselbalch equa

Lactic acid (CH3 CHOHCO2 H) is found in sour milk, in...

Lactic acid $\left(\mathrm{CH}_{3} \mathrm{CHOHCO}_{2} \mathrm{H}\right)$ is found in sour milk, in sauerkraut, and in muscles after activity. $\left(K_{\mathrm{a}} \text { for lactic acid }=1.4 \times 10^{-4} .\right)$ (a) If $2.75 \mathrm{g}$ of $\mathrm{NaCH}_{3} \mathrm{CHOHCO}_{2}$, sodium lactate, is added to $5.00 \times 10^{2} \mathrm{mL}$ of $0.100 \mathrm{M}$ lactic acid, what is the $\mathrm{pH}$ of the resulting buffer solution? (b) Is the $\mathrm{pH}$ of the buffered solution lower or higher than the $\mathrm{pH}$ of the lactic acid solution?

Lactic acid $\left(\mathrm{CH}_{3} \mathrm{CHOHCO}_{2} \mathrm{H}\right)$ is found in sour milk, in sauerkraut, and in muscles after activity.
$\left(K_{\mathrm{a}} \text { for lactic acid }=1.4 \times 10^{-4} .\right)$
(a) If $2.75 \mathrm{g}$ of $\mathrm{NaCH}_{3} \mathrm{CHOHCO}_{2}$, sodium lactate, is added to $5.00 \times 10^{2} \mathrm{mL}$ of $0.100 \mathrm{M}$ lactic acid, what is the $\mathrm{pH}$ of the resulting buffer solution?
(b) Is the $\mathrm{pH}$ of the buffered solution lower or higher than the $\mathrm{pH}$ of the lactic acid solution?

Key Concepts

Buffer Solutions

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base (or a weak base and its conjugate acid), which work together to neutralize added H+ or OH- ions, thus maintaining a relatively constant pH in the solution.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a key tool for calculating the pH of a buffer solution. It relates the pH of the solution to the pKa of the weak acid and the ratio of the concentrations of its conjugate base and the acid. Specifically, it is expressed as pH = pKa + log([conjugate base]/[acid]), providing an easy way to predict how modifications in concentration will affect the pH.

Acid Dissociation Constant (Ka) and pKa

The acid dissociation constant (Ka) defines the equilibrium between a weak acid and its ions in solution, while pKa, the negative logarithm of Ka, is used to express acid strength on a convenient scale. Understanding these values is crucial in buffer calculations, as they determine the degree of ionization of the acid and help dictate the outcome of the pH in the buffer system.

Conjugate Acid-Base Pair

A conjugate acid-base pair consists of a weak acid and the corresponding species formed when the acid donates a proton, which is its conjugate base. In buffer solutions, these pairs work together to stabilize the pH, since the conjugate base can react with added acids and the weak acid can react with added bases, thereby compensating for changes in hydrogen ion concentration.

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