• In acid-base titrations/reactions, are dealing with neutralization reactions (Use NmN Tables→ water is not a reactant)

            ○ N: neutralization reaction

            ○ M: mmols                                                                                                                                 

                      ■ In ice table, subtract number of mmols of limiting reactant

           ○ N: numbers

  • Millimoles:

          ○ Ex: 40 mL x 0.2 M = 8 mmol

                      ■ To convert back into concentration, do mmol/mL

  • Halfway point/halfway equivalence point: half of the analyte has been neutralized

           ○ At halfway point pH = pKa; molarity of weak acid and conjugate base is equal; buffer is most effective

  • Buffer Zone: region between the initial and eq. point; includes the halfway point
  • What if you combine equal amounts of weak acid and weak base?

           ○ Solution will be acidic if Ka (of conjugate acid) is larger than Kb (of conjugate base) b/c more H3O+ ions are produced than OH- ions

Strong Acid-Strong Base Titrations

  • They both dissociate completely

             ○ Strong acids: molarity of acid = molarity of H+                                               

             ○ Strong Base: molarity of base = molarity of OH-

  • The net ionic reaction for a strong acid–strong base titration is:
  • Don’t need to do double ICE table at equilibrium (only NmN)
  • pH is equal to 7 at the eq. point (only for strong + strong)

Weak Acid-Strong Base Titration

  • The weaker the acid being titrated, the smaller the vertical area around the equivalence point
  • pH at equivalence is above 7
  • At 0 mL base added: use WMX ICE table, use Ka to determine pH
  • Weak acid before eq point:

              ○ NmN ICE table first

              ○ Then Henderson-Hasselbalch

  • At eq point: Have to do double ICE tables (only at the eq point)

             ○ NmN ICE table first → will have conjugate base left over

             ○ Then, WMX ICE table, use Kb to find [OH-]

  • pH after equivalence:

              ○ NmN ICE table first → leftover strong base → do mmol/mL to find moles of [OH-] → find pOH- → find pH

Weak Base-Strong Acid Titration

  • Process is practically the same with some differences
  • pH at equivalence is below 7
  • At 0 mL acid added:

             ○ WMX ICE table, use Kb to determine pOH, then pH

  • Weak base before equivalence point:

              ○ NmN ICE table first → then Henderson-Hasselbalch (will have to use Kb to solve for pKa)

  • At equivalence point:

               ○ NmN ICE table first → will have conjugate acid left over

               ○ Then do WMX ICE table → use Ka to find [H+]

  • pH after equivalence:

               ○ NmN ICE table first → leftover strong acid → do mmol/mL to find moles of [H+] → find pH

Titration Curves

Strong Acid-Strong Base Titration

  • Before the eq point: → Have left over strong acid (H+) which is why the pH is below 7

  • For strong + strong only, the pH at eq. point is exactly 7
  • Everywhere beyond equivalence point: have excess OH- which is why the pH is above 7

Weak Acid-Strong Base Titration

Graph:

At eq point only the conjugate base is present which is why the eq point is above 7

           ○ Justify: b/c this reaction  takes place

Weak Base-Strong Acid Titration

  • In buffer zone 25mL is halfway point pH = pKa

               ○

  • At eq point only the conjugate acid is present which is why the eq point is below 7

           ○ Justify: because this reaction takes place

  • Beyond eq point have left over H+ 

Sketching a Titration Curve

  • Need to plot 3 data point:
  1. Starting PH
  2. pH at equivalence
  3. pH at the halfway point
  • If given pkB, can solve for pKa to find pH