Calculate the [H+] in a solution containing 1.00 M hydroflouris acid (Ka=7.2 x 10^-4) and .50 M sodium fluoride
This is the Henderson-Hasselbalch equation (the buffer equation).
pH = pKa + log (base)/(acid)
F^- is the base.
HF is the acid.
To calculate the [H+] in the solution, we need to consider the dissociation of hydrofluoric acid (HF) and the formation of the fluoride ion (F-) from sodium fluoride (NaF).
1. Identify the chemical equation for the dissociation of hydrofluoric acid (HF):
HF ⇌ H+ + F-
2. Write the equilibrium expression (Ka) for hydrofluoric acid:
Ka = [H+][F-] / [HF]
3. Use the given concentration of hydrofluoric acid (1.00 M) and the known Ka value (7.2 x 10^-4) to determine the equilibrium concentrations:
Let x represent the concentration of [H+] and [F-] produced.
[HF] = 1.00 M - x
[H+] = x
[F-] = x
4. Substitute the equilibrium concentrations into the Ka expression:
Ka = [H+][F-] / [HF]
7.2 x 10^-4 = x * x / (1.00 - x)
5. Simplify the equation:
7.2 x 10^-4 = x^2 / (1.00 - x)
6. Solve for x using the quadratic formula:
Quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a
In this case, a = 1, b = 0, and c = -7.2 x 10^-4:
x = (-0 ± √(0 - 4(1)(-7.2 x 10^-4))) / 2(1)
x = (√2.88 x 10^-3) / 2
7. Calculate the value of x:
x ≈ 0.029
8. Determine the concentration of [H+]:
[H+] ≈ 0.029 M
Therefore, the concentration of [H+] in the solution is approximately 0.029 M.