Weak Acid pH Calculator
Calculate the pH of a weak acid solution from Ka and initial concentration
HA = H+ + A-
Common Weak Acids:
pH
2.8724
pOH
11.1276
[H+]
1.3416e-3 M
pKa
4.7447
% Ionization
1.3416%
Equilibrium Concentrations:
[HA] = 9.8658e-2 M
[A-] = 1.3416e-3 M
[H+] = 1.3416e-3 M
[OH-] = 7.4536e-12 M
Method Comparison:
Exact [H+]: 1.3327e-3 M
Approx [H+]: 1.3416e-3 M
Calculating Weak Acid pH
For a weak acid HA with initial concentration C and dissociation constant Ka, the pH can be calculated using the equilibrium expression Ka = [H+][A-]/[HA].
Approximation Method
[H+] = sqrt(Ka x C)
Valid when % ionization < 5%
Exact (Quadratic) Method
[H+] = (-Ka + sqrt(Ka^2 + 4KaC)) / 2
Always accurate