Final answer:
To calculate the mass of NaOH a buffer solution can neutralize before the pH rises, use the Henderson-Hasselbalch equation along with the molarity and molar mass of NaOH, leading to the conclusion that this buffer can neutralize 2.31 grams of NaOH.
Step-by-step explanation:
To determine what mass of NaOH this buffer solution can neutralize before the pH rises above 4.00, we can apply Henderson-Hasselbalch equation and stoichiometry. Using the given Ka for HF (3.5×10⁻⁴), and the concentration of HF and NaF (0.170 M), we can set up the equation to solve for the pH when HF is converted to F− by OH−, as NaOH is a strong base it will completely dissociate and react with HF.
The buffer capacity depends on the amount of HF and F− available to react with NaOH. We use the equation n(NaOH) = n(HF) to determine the moles of NaOH that can be neutralized. Since the concentrations are equal, the ratio of HF/F− after neutralization will remain 1:1 until all HF has been converted.
To find the mass of NaOH that can be neutralized, we compute the moles of HF available, then convert that to moles of NaOH using the 1:1 stoichiometry between HF and NaOH. Finally, we use the molar mass of NaOH to find the mass.
Molar mass of NaOH = 22.99 (Na) + 15.99 (O) + 1.01 (H) = 39.99 g/mol. The moles of HF is 0.170 moles/L × 0.340 L = 0.0578 moles. This is also the moles of NaOH that can be neutralized. Hence, the mass of NaOH = 0.0578 moles × 39.99 g/mol = 2.31 grams.