Question

A buffer contains the weak acid HA and its conjugate base A−. The weak acid has a pKa of 4.36 and the buffer has a pH of 4.92. Which statement is true of the relative concentrations of the weak acid and conjugate base in the buffer?

-HA] > [A−]
-[HA] < [A−]
-[HA] = [A−]

Which buffer component would you add to change the pH of the buffer to 4.72?

Answer 1

The concentration of the conjugate base is greater than the concentration of the weak acid in the buffer solution. To change the pH to 4.72, you should add more of the weak acid to the buffer.

Step-by-step explanation:

The relative concentrations of the weak acid and conjugate base in the buffer can be determined using the Henderson-Hasselbalch equation, which states that pH = pKa + log10([A-]/[HA]). In this case, the buffer has a pH of 4.92, which is greater than the pKa of the weak acid (4.36). Since pH > pKa, the concentration of the conjugate base ([A-]) is greater than the concentration of the weak acid ([HA]). Hence, the correct statement is [HA] < [A-].

To change the pH of the buffer to 4.72, you would need to adjust the relative concentrations of the weak acid and conjugate base. Since the buffer currently has a pH greater than the desired pH, you would need to increase the concentration of the weak acid ([HA]). By doing so, the ratio [A-]/[HA] will decrease, resulting in a lower pH. Therefore, you should add more of the weak acid (HA) to the buffer solution.