For this problem, we have to calculate the pH when 49.5 mL of 0.335 M NaA is mixed with 30.6 mL of 0.120 M HCl.

- HF and NaF are conjugate pairs, hence we can use Henderson-Hasselbach equation to calculate the pH
- To do so, follow these steps

**Step 1. **Find the moles of F^{- }and HF

**Step 2. **Calculate the pH using HH equation

(1) Moles of A^{- }will be calculated as:

Calculate the pH of a solution prepared by mixing 50 mL of a 0.10 M solution of HF with 25 mL of a 0.20 M solution of NaF. pK_{a} of HF is 3.14.

A) 5.83

B) 12.00

C) 3.14

D) 7.35

E) 10.80