a 0,25M solution of a week acid is 3% dissociated.calculate ka
0.25 x 0.003 = 7.5E-4
..............HA ==> H^+ + A^-
initial.......0.25.....0.....
change.....-7.5E-4...7.4E-4..7.5E-4
equl..........?........?......?
Ka = (H^+)A^-)/(HA)
Substitute and solve for Ka.
To calculate the Ka (acid dissociation constant) of a weak acid, we need to know the degree of dissociation and the initial concentration of the acid.
Given:
- Concentration of the weak acid solution = 0.25 M
- Degree of dissociation (α) = 3% or 0.03
The equation for the dissociation of a weak acid is:
HA ⇌ H+ + A-
The initial concentration of the weak acid (HA) can be used to calculate the equilibrium concentrations of the dissociated species (H+ and A-) using the degree of dissociation. Since the degree of dissociation is given as a percentage, we can calculate the concentration of dissociated species as follows:
[H+] = α * [HA]
[A-] = α * [HA]
So, [H+] = 0.03 * 0.25 M = 0.0075 M
[A-] = 0.03 * 0.25 M = 0.0075 M
The Ka can be calculated using the equation:
Ka = [H+] * [A-] / [HA]
Substituting the values we have:
Ka = (0.0075)(0.0075) / (0.25)
= 0.00005625 / 0.25
= 0.000225
Therefore, the Ka value for the weak acid is approximately 0.000225.