If 10.0 g of NaF and 15.0 g of HF are dissolved in water to make 2.0 L of solution, what is the pH of the resulting solution?

2.68

Explanation:

Step 1: Calculate the molar concentrations of the solutes

We will use the following expression.

M = mass of solute / molar mass of solute × liters of solution

[HF] = 15.0 g / 20.01 g/mol × 2.0 L = 0.37 M

[NaF] = 10.0 g / 41.99 g/mol × 2.0 L = 0.12 M

Step 2: Calculate the pH of the solution

We have a buffer system formed by a weak acid (HF) and its conjugate base (F⁻ coming from NaF). We can calculate the pH of the solution using Henderson-Hasselbach equation.

pH = pKa + log [F⁻]/[HF]

pH = 3.17 + log (0.12 M/0.37 M)

pH = 2.68