acids, bases, pH + buffers

week 7, question 3

ka expression for weak acid

Ka = [H+]² / [HA]

assumptions of weak acids

[H+] = [A-]

ionic product of water

Kw = [H+] [OH-] = 10^-14

ionisation of water is

endothermic = eqm shifts RIGHT if temp is INCREASED = Kw INCREASES = pH DECREASES

weak acids

partially dissociate

strong acids

completely dissociate

pKa =

-log[Ka]

buffer solutions

resist changes in pH when a small amount of acid/base is added

pH of buffers

<7

how are buffers made

mixture of weak acid and one of its salts (conjugate base)

salt/conjugate base

completely dissociates (buffers)

higher Ka =

stronger acid

pH of acidic buffer solution

[H+] = Ka [A-] / [HA]

lower Pka =

stronger acid

Henderson-Hasselbalch equation

pH= pKa​ + log([A−]​ / [HA])