Titrations

acid–base titration

a solution of unknown concentration (analyte) reacts with a solution of known concentration (titrant)

equivalence point

1. number of moles of titrant=number of moles of analyte

2. neither reactant is in excess

3. the reaction is complete

titration curve

plot of the pH of the analyte solution versus the volume of the titrant added

strong acid—strong base titration

• curve begins acidic and turns basic after the equivalence point

• neutral at equivalence point

strong base—strong acid titration

• curve begins basic and turns acidic after the equivalence point

• neutral at equivalence point

weak acid—strong base titration

• pH = pK_a at the ½ - equivalence point

• basic at equivalence point

weak base—strong acid titration

• pH = pK_a at the ½ - equivalence point

• acidic at equivalence

polyprotic acid

acid that has more than one ionizable proton and dissociates in a stepwise manner

• Only the first dissociation step makes a significant contribution to [H₃O⁺] because the K_a gets significantly smaller with each step