Acid-Base Titrationsprogressive addition of one reactant to

another in measured volumes until an endpoint is reached.

equivalence point (mL) is when the mole

ratio is exactly satisfied, volume used for stoichiometry

is shown by an indicator which changes color at the endpoint (pH)

Buffering: area where the pH is constant/little change even thought the titrant is being added.

pH Titration Curves Titration of Sample with Titrant

A. Strong Base with a Strong Acid

Titration of NaOH with HCl

-sudden pH change, steep curve-endpoint is at pH = 7-H30+

(aq) + OH-(aq) H20(l)

B. Weak acid with a Strong Base

Titration of HCN with NaOH

-less steep curve

-endpoint is pH>7,

-Ex) HCN(aq) + OH-(aq) CN-(aq) + H20(l), CN- is a weak base so

pH>7

then CN-(aq) + H20(l ) HCN(aq) + OH-(aq) , OH- increases pH

C) Weak Base with a Strong Acid

Titration of NH3 with HCl

-less steep curve

-endpoint is pH<7

-Ex) NH3(aq) + H30+(aq) NH4

+(aq) + H20(l), NH4

+ is a weak acid so

pH<7

then NH4+

(aq) + H20(l ) NH3(aq) + H30+(aq) , H30+ decreases pH

D. Weak Base with Weak Acid

Titration of F- with HCN

-difficult to see endpoint without curve-pH stays near 7, either acidic or basic depending on Ka/Kb- F-

(aq) + HCN (aq) HF(aq) + CN-(aq)