Calculate the pH of a solution prepared by mixing 25.0 mL of 0.60 M HC2H3O2 and 15.0 mL of 0.60 M NaC2H3O2?

Use the Henderson-Hasselbalch equation.

but then what is the pka?

what is the pKa?

To calculate the pH of the solution, we need to determine the concentration of H+ ions in the final solution. The solution is prepared by mixing a weak acid (HC2H3O2) with its conjugate base (NaC2H3O2). This is a buffer solution.

To calculate the concentration of H+ ions in the buffered solution, we can use the Henderson-Hasselbalch equation:

pH = pKa + log ([A-] / [HA])

Where:
pH = the pH of the solution
pKa = the acid dissociation constant of the weak acid (HC2H3O2)
[A-] = the concentration of the conjugate base (NaC2H3O2)
[HA] = the concentration of the weak acid (HC2H3O2)

First, we need to find the pKa value of HC2H3O2. The pKa of acetic acid (HC2H3O2) is approximately 4.76.

Next, we need to determine the concentration of [A-] and [HA] in the buffer solution.

[A-]:
The conjugate base, NaC2H3O2, fully dissociates in water to form C2H3O2- ions. The concentration of the conjugate base in the final solution can be calculated using the following formula:

[A-] = (volume of NaC2H3O2 / total volume of the solution) × concentration of NaC2H3O2

Substituting the values:
[A-] = (15.0 mL / (15.0 mL + 25.0 mL)) × 0.60 M = 0.20 M

[HA]:
The weak acid, HC2H3O2, partially dissociates in water. However, for most cases, the extent of dissociation will be negligible. Hence, we can assume that the concentration of weak acid is equal to its initial concentration.

[HA] = concentration of HC2H3O2 = 0.60 M

Now we can substitute the values into the Henderson-Hasselbalch equation:

pH = 4.76 + log (0.20 M / 0.60 M)

pH = 4.76 + log (1/3)

pH = 4.76 - 0.52

pH = 4.24

Therefore, the pH of the solution prepared by mixing 25.0 mL of 0.60 M HC2H3O2 and 15.0 mL of 0.60 M NaC2H3O2 is approximately 4.24.