A2 Chemistry – Acid Base Equilibria – 2012 -2013 – T. A. Aoudi

pH = – log[H+]

[H+]= Ka × [weak acid]

Weak acid,HA

[H+] =

Buffer (acidic)

[Weak acid]

[Conj. base] Ka ×

[OH–]= Kb× [weak base]

[H+] =

Kw

[OH–]

Weak base Buffer (basic)

[OH–] =

[H+] =

Kb × [Weak base]

[Conj. acid]

Kw

[OH–]

Strong base

[H+] =

[OH–]

Kw

CH3NH2(aq) + H2O = CH3NH3+(aq) + OH–

KOH (aq) K+(aq) + OH–(aq)

Use Kw to find [H+]

Strong acid (monobasic)

[H+] = [strong acid]

[H+] = Kw at any temp.

Pure(de–ionised) water

[H+] = [OH-]