pH is a number that is a property of a solution (pH = -log[H3O+]) where [H3O+] is in .
pH is measured with a pH meter or pH paper
pH depends on which acids and bases are present and their concentration.
The acidity constant Ka is a number that is a property of an acid-base conjugate pair.
Examples of these are
CH3CO2H (acid) and CH3CO2– (conjugate base)
NH4+ (acid) and NH3 (conjugate base)
Ka is an equilibrium constant. This number is equal to the combination of concentrations at equilbrium in the reaction quotient defined for the reaction of one mole of the acid with water.
Because the form of the reaction quotient expression is the same for all acid-base conjugate pairs, comparison of Ka for two acid-base conjugate pairs indicates the relative tendency of the two acids to donate a proton.
For stronger acids, Ka is higher as the tendency of the acid to donate H+ is higher.
pH is measured with a pH meter or pH paper
pH depends on which acids and bases are present and their concentration.
The acidity constant Ka is a number that is a property of an acid-base conjugate pair.
Examples of these are
CH3CO2H (acid) and CH3CO2– (conjugate base)
NH4+ (acid) and NH3 (conjugate base)
Ka is an equilibrium constant. This number is equal to the combination of concentrations at equilbrium in the reaction quotient defined for the reaction of one mole of the acid with water.
acid + H2O 
H3O+ + conjugate base
Reaction quotient expressions have products in the numerator and reactants in the denominator. Each concentration is raised to a power equal to its coefficient in the balanced equation for the reaction.
The magnitude of Ka is the same for a particular acid-base conjugate pair irrespective of how the solution was prepared. This is because solutions of weak acids and bases reach equilibrium on mixing.
H3O+ + conjugate baseReaction quotient expressions have products in the numerator and reactants in the denominator. Each concentration is raised to a power equal to its coefficient in the balanced equation for the reaction.
| Ka = | [conjugate base ][H3O+] |
| [acid] | |
| number | reaction quotient |
The magnitude of Ka is the same for a particular acid-base conjugate pair irrespective of how the solution was prepared. This is because solutions of weak acids and bases reach equilibrium on mixing.
Because the form of the reaction quotient expression is the same for all acid-base conjugate pairs, comparison of Ka for two acid-base conjugate pairs indicates the relative tendency of the two acids to donate a proton.
For stronger acids, Ka is higher as the tendency of the acid to donate H+ is higher.
The forward reaction is more significant (higher [conjugate base] than [acid] at equilibrium).