Acids Lesson 18 Titration Curves

Titration Curves  A titration curve is a graph of the pH versus the volume in a titration. The equivalence point is the end of a titration where the stoichiometry of the reaction is exactly satisfied. moles H+ = moles OH- The transition point is when an indicator changes color and [HInd] = [Ind-].

Choosing an Indicator When you choose an indicator, you must pick one so that the transition point of the indicator matches the equivalence point of the titration.   Rule of thumb Salt Equivalence Point Neutral 7 Basic 9 Acidic 5

is added to 1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH neutral salt pH = 7 Bromothymol Blue- see page 7 data 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl is added to We start here pH Volume 0.10 M KOH added 14 7 25 50

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + H2O basic salt Indicator pH = 9 Phenolphthalein- see page 7 data 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH is added to pH Volume 1.0 M HCN added 14 7 10 20

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4Cl acid salt Indicator pH = 5 Methyl Red- see page 7 data 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 30 60

6. Match the Curve with the Reaction pH Volume .10 M KOH added 14 7 25 50 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH C. HCN + KOH → KCN + HOH B. HCl + KOH → KCl + HOH

6. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 30 60 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

6. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 30 60 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH