Question

calculate the [h3o ] of a solution that is 0.2 m in hf and 0.1 m naf a = 7.2 × 10-4 for HF.a. 6.3 × 10–5 M b. 1.4 × 10–3 M c. 5.0 × 10–3 M d. 3.2 × 10–4 M e. 4.0 × 10–6 M

Answer 1

To find the [H3O+] of a 0.2 M HF and 0.1 M NaF solution, we apply the Henderson-Hasselbalch equation and calculate a pH of 2.84, leading to an [H3O+] of about 1.4 × 10^-3 M.

Step-by-step explanation:

To calculate the concentration of hydronium ions ([H3O+]) in a solution containing hydrofluoric acid (HF) and sodium fluoride (NaF), we need to apply the Henderson-Hasselbalch equation. The given acid dissociation constant (Ka) for HF is 7.2 × 10^-4. With the concentrations of HF and NaF at 0.2 M and 0.1 M respectively, we are looking at a buffer system.

First, calculate the ratio of the base to acid, which should be the concentration of NaF (the salt providing the conjugate base F-) divided by the concentration of HF (the acid):

[Base]/[Acid] = [F-]/[HF] = 0.1 M /0.2 M = 0.5

Using the Henderson-Hasselbalch equation:

pH = pKa + log([Base]/[Acid])

Substituting the known values:

pH = -log(7.2 × 10^-4) + log(0.5)

pH ≈ 3.14 + (-0.3010) ≈ 2.84

Then, to find [H3O+], take the inverse log of the negative pH:

[H3O+] = 10^-pH = 10^-2.84 ≈ 1.4 × 10^-3 M

Therefore, the concentration of hydronium ions in this buffer solution is approximately 1.4 × 10^-3 M, which matches option (b).

Answer 2

To calculate the [H3O+] of a solution containing HF and NaF, we can use the Henderson-Hasselbalch equation. Plugging in the given concentrations and Ka value for HF, we can solve for the [H3O+] of the solution. The correct answer is approximately 6.3x10^-5 M.

Step-by-step explanation:

To calculate the [H3O+] of a solution that is 0.2 M in HF and 0.1 M in NaF, we can use the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation relates the pH of a solution to the ratio of the concentration of the conjugate base to the concentration of the acid. In this case, HF is the acid and F- is the conjugate base.

We are given a Ka value for HF of 7.2x10^-4. Using this information, we can calculate the ratio of [F-] to [HF] using concentration values of 0.1 M and 0.2 M, respectively. Plugging these values into the equation and solving for the pH, we find that the [H3O+] of the solution is approximately 6.3x10^-5 M, which corresponds to answer choice A.