weak acid strong base titration curve

A. Point 1

• to get pH: Do a RICE problem with the [initial] of acid

• before titration begins

B. Region A

• before equivalence point

• middle part of this region doesnt change much because its a buffer

• to get pH: determine moles of acid remaining and moles of conjugate base produced, divide both by new total volume, plug into H-H equation

• [HA] > [A-] in this region before midpoint

C. Point 3

• indicator should have a pka = pH at this point

• to get pH: determine moles of conjugate base produced, divide by new total volume, use RICE problem of conjugate base with water to determine pH

• moles of acid you started with equals moles of base added

• indicator should (if chosen correctly) change colour here

• equivalence point

• can be seen on pH curve by picking a point half-way up rapid rise region

• can be used to calculate molarity or weight % of analyte

D. Region B

• to get pH: determine moles of base/titrant remaining, divide by new total volume, and take -log[base] and subtract by 14

• beyond equivalence point

• excess base has been added beyond the point at which all the acid has been neutralized

• [HA] = 0 pretty much

• [A-] can be ignored but is present

E. Point 2

• moles of base added equals half the moles of acid you started with

• volume of titrant added equals half the volume of titrant added at equivalence point

• [HA] = [A-]

• half-equivalence point

• pH = pKa

• midpoint

• can be used to determine identity of unkown acid based on Ka