HZ is a weak acid. A concentration of 0.020M in aqueous solution gives a pH of 4.93 what is the Ka?
...............HZ ==> H^+ + Z^-
initial........0.02...0.....0
change..........-x....x......x
equil.........0.02-x..x......x
Ka = (H^+)(Z^-)/(HZ)
You know H^+ by solving pH = -log(H^+) (that's the x)
Z= x and that's the same as (H^+).
HZ = 0.02-x = 0.02-(H^+).
Substitute into Ka expression and solve for Ka. I get approximately 7E-9
To find the Ka (acid dissociation constant) for the weak acid HZ, we need to use the given information about its concentration and pH.
The pH of a solution is related to the concentration of H+ ions using the equation: pH = -log[H+]
We know that the pH of the solution is 4.93, so we can calculate the concentration of H+ ions using this equation:
[H+] = 10^(-pH)
[H+] = 10^(-4.93)
[H+] = 7.94 x 10^(-5) M
Assuming that HZ completely dissociates into H+ and Z- in solution, and since the concentration of H+ ions is the same as the concentration of HZ, the concentration of HZ is also 7.94 x 10^(-5) M.
Now, we can use the formula for Ka to calculate its value:
Ka = [H+][Z-] / [HZ]
Since the concentration of HZ is the same as [H+], we can say:
Ka = (7.94 x 10^(-5))^2 / (7.94 x 10^(-5))
Simplifying the equation:
Ka = (7.94 x 10^(-5))^2 / (7.94 x 10^(-5))
Ka = 6.29 x 10^(-9)
Therefore, the Ka of HZ is 6.29 x 10^(-9).
To find the Ka (acid dissociation constant) of HZ, we can use the fact that the pH of the solution is provided and HZ is a weak acid. The pH of a solution gives us the concentration of H3O+ (hydronium ions) present.
First, we need to calculate the concentration of H3O+ ions in the solution based on the pH value. We can use the following equation:
pH = -log[H3O+]
Since the pH is 4.93, we can rearrange the equation to find [H3O+]:
[H3O+] = 10^(-pH)
[H3O+] = 10^(-4.93)
[H3O+] = 7.07 x 10^(-5) M
Now, let's write the dissociation equation for HZ:
HZ ⇌ H+ + Z-
The initial concentration of HZ is 0.020 M, and at equilibrium, the concentration of H+ ions will be equal to the concentration of Z- ions, as HZ is a monoprotic acid.
Let's assume the concentration of H+ (and Z-) ions at equilibrium is x M. Then, the equilibrium concentration of HZ will be (0.020 - x) M.
Since HZ is a weak acid, we can use the expression for the acid dissociation constant (Ka):
Ka = [H+][Z-] / [HZ]
Substituting the known values:
Ka = x * x / (0.020 - x)
Since the concentration of H+ ions is equal to the concentration of Z- ions, we can simplify the equation:
Ka = x^2 / (0.020 - x)
Now, we need to determine the value of x. Since the concentration of H+ ions is equal to the concentration of Z- ions, and we calculated the concentration of H3O+ ions in the solution earlier, we can say:
x = [H+] = [H3O+] = 7.07 x 10^(-5) M
Substituting this value into the equation:
Ka = (7.07 x 10^(-5))^2 / (0.020 - 7.07 x 10^(-5))
Calculating this expression will give us the value of Ka.