Question

calculate the ph of a solution that is made by combining 55 ml of 0.040 m hydrofluoric acid with 125 ml of 0.100 m sodium fluoride.

Answer 1

The pH of a solution of hydrofluoric acid and sodium fluoride can be calculated using the Henderson-Hasselbalch equation, taking into account the concentration ratios of the fluoride ion and hydrofluoric acid and their dissociation constant.

Step-by-step explanation:

To calculate the pH of the mixed solution containing hydrofluoric acid (HF) and sodium fluoride (NaF), we will use the concept of buffers and the Henderson-Hasselbalch equation. This calculation is based on weak acid/strong base mixture and the dissociation constant (Ka) of hydrofluoric acid.

First, we need to calculate the moles of HF and NaF in the solution:

• HF: 0.055 L × 0.040 M = 0.0022 mol
• NaF: 0.125 L × 0.100 M = 0.0125 mol

Since NaF is the salt of the weak acid and will completely dissociate into Na+ and F- ions, the concentration of F- ions will be equal to the initial concentration of NaF. As the solution is mixed, HF may dissociate or associate according to the reaction F⁻ (aq) + H₂O (l) ≈ HF (aq) + OH⁻ (aq).

Given the Ka of HF is 1.4 × 10−11, we can find the pKa (=-log(Ka)) and use it in the Henderson-Hasselbalch equation:

pH = pKa + log([A⁻]/[HA])

By substituting the values, we obtain the pH of the buffer solution.

Answer 2

To calculate the pH of the solution, find the concentration of the hydronium ion (H+). Use the formula moles = molarity x volume to calculate the moles of hydrofluoric acid (HF) and sodium fluoride (NaF). Then, calculate the H+ concentration using the formula H+ concentration = moles of HF / total volume. Finally, use the formula pH = -log[H+] to find the pH.

Step-by-step explanation:

To calculate the pH of the solution, we need to find the concentration of the hydronium ion (H^+).

First, calculate the moles of hydrofluoric acid (HF) using the formula:

moles = molarity x volume

moles of HF = (0.04 M) x (0.055 L) = 0.0022 mol

Similarly, calculate the moles of sodium fluoride (NaF):

moles of NaF = (0.1 M) x (0.125 L) = 0.0125 mol

Next, find the total volume of the solution:

volume = 0.055 L + 0.125 L = 0.18 L

Now, calculate the concentration of the hydronium ion (H^+) using the formula:

H^+ concentration = moles of HF / total volume

H^+ concentration = 0.0022 mol / 0.18 L = 0.0122 M

To calculate the pH, use the formula:

pH = -log[H^+]

pH = -log(0.0122) ≈ 1.91