A weak acid solution, HX 0.37 M, has a pH of 3.70. Calculate the acidity constant for this acid.
pH = -log(H^+)
3.70 = -log(H^+)
Convert that; I get about 2E=4 but you need to confirm that.
...........HX ==> H^+ + X^-
I.........0.37....0......0
C........-2E-4...2E-4...2E-4
E......0.37-2E-4..2E-4...2E-4
Substitute into the Ka expression and solve for Ka.
To calculate the acidity constant (Ka) for a weak acid, we can use the pH and the initial concentration of the acid.
The equation for the acid dissociation reaction is:
HX ⇌ H+ + X-
The pH of a solution is related to the concentration of H+ ions by the following equation:
pH = -log[H+]
Given that the pH is 3.70, we can calculate the concentration of H+ ions using the equation:
[H+] = 10^(-pH)
[H+] = 10^(-3.70)
[H+] = 0.0001995 M (approximately)
The concentration of the acid (HX) is given as 0.37 M.
The equilibrium expression for the dissociation of the weak acid is:
Ka = [H+] [X-] / [HX]
Substituting the values, we get:
Ka = (0.0001995) (0.0001995) / (0.37)
Ka = 0.00000000198 / 0.37
Ka ≈ 5.35 x 10^-9
Therefore, the acidity constant (Ka) for the weak acid HX is approximately 5.35 x 10^-9.
To calculate the acidity constant (Ka) for the weak acid solution, we need to use the pH value and concentration of the acid.
The pH is related to the hydrogen ion concentration (H+) by the equation: pH = -log[H+]
We can calculate [H+] using the pH value:
[H+] = 10^(-pH)
Given that the pH is 3.70, we can find [H+]:
[H+] = 10^(-3.70)
Next, we use the concentration of the acid (HX) to find the initial concentration of [HX]:
[HX] = 0.37 M
Assuming the weak acid (HX) completely dissociates, the concentration of [H+] and [X-] (from HX) after dissociation will both be equal.
Thus, [H+] = [X-] = x (let's assume it to be x)
The equilibrium equation for the dissociation of the weak acid is:
HX ⇌ H+ + X-
The Ka expression for the weak acid is as follows:
Ka = [H+][X-] / [HX]
Substituting the values we found,
Ka = x * x / 0.37
We know that [H+] = x, so we can rewrite the equation as:
Ka = [H+]^2 / 0.37
Now, substitute the value of [H+], we calculated earlier:
Ka = (10^(-3.70))^2 / 0.37
Calculating the Ka for the given weak acid solution:
Ka = 1.995e-7 / 0.37
Ka ≈ 5.39e-7