Calculate the volume (mL) of 0.500 M NaOH required to reach the equivalence point in the titration of 25.0 mL of 0.650 M HF. K_a for HF = 3.5 × 10⁻⁴.

• A. 16.3 mL
• B. 19.2 mL
• C. 30.8 mL
• D. 32.5 mL
• E. 88.0 mL

Answer: (D)

Verified step by step guidance

1. Start by understanding the concept of titration and equivalence point. The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance present in the solution being titrated.
2. Write the balanced chemical equation for the reaction between NaOH and HF: \( \text{NaOH} + \text{HF} \rightarrow \text{NaF} + \text{H}_2\text{O} \). This shows a 1:1 molar ratio between NaOH and HF.
3. Calculate the moles of HF present in the solution using the formula \( \text{moles} = \text{concentration} \times \text{volume} \). For HF, \( \text{moles of HF} = 0.650 \text{ M} \times 25.0 \text{ mL} \times \frac{1 \text{ L}}{1000 \text{ mL}} \).
4. Since the reaction is 1:1, the moles of NaOH required will be equal to the moles of HF. Use the concentration of NaOH to find the volume needed: \( \text{volume of NaOH} = \frac{\text{moles of NaOH}}{\text{concentration of NaOH}} \).
5. Convert the volume of NaOH from liters to milliliters by multiplying by 1000, as the final answer should be in mL.