Answer :
Final answer:
To calculate the pH after adding KOH to a buffer solution of HF and NaF, one must consider the stoichiometric reaction between KOH and HF and use the Henderson-Hasselbalch equation. The pH of an unbuffered solution, in comparison, would change significantly after the addition of NaOH.
Explanation:
Calculating the pH of a Buffer Solution
We are asked to calculate the pH of a buffered solution after the addition of KOH. The buffer is composed of HF and its conjugate base NaF, both at 0.271 M concentration. When 0.077 mol of KOH is added to 1.69 L of this buffer, the KOH will react with the HF to form water and F-.
The Henderson-Hasselbalch equation is used to calculate the pH of buffer solutions:
-]/[HA])
For HF, the pKa is approximately 3.17. To find the new concentrations, we must account for the reaction between KOH and HF, where KOH is a strong base and will consume HF. Given the 1:1 stoichiometry between KOH and HF, the number of moles of HF will decrease by 0.077 mol, and the concentration of F- will increase by 0.077 mol.
After adjusting the concentrations, we can use the Henderson-Hasselbalch equation to find the new pH. However, to compare with an unbuffered solution, we also look at the pH change after adding 1.0 mL of 0.10 M NaOH to 100 mL of an unbuffered solution with a pH of 4.74. In contrast to the buffered system, the pH of the unbuffered solution will change much more significantly because there is no conjugate base to mitigate the addition of the strong base NaOH.
Using the given information and assuming there are no significant volume changes due to the addition of solid KOH, the pH of the buffer after the addition of KOH would be calculated as follows. However, the detailed calculation is not provided here, as it would require additional information such as the pKa of HF and the final volume of the buffer solution.
