1. Weak Acid/Strong Base calculations
Acids & Bases
Lesson 12
Titration Curves &
Weak Acid/Strong Base calculations

2. Titration Curves
 A titration curve is a graph of the pH changes that occur during an acid-base titration versus the volume of acid or base added.
The equivalence point is the end of a titration where the stoichiometry of the reaction is exactly satisfied, or moles H+ = moles OH-.
The transition point refers to when an indicator changes color and [HInd] = [Ind-].

3. Three types of Titrations
Strong acid and strong base
Weak acid and strong base
Weak base and strong acid

4. 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.
Look at the salts produced, if
Rule of thumb Salt Equivalence Point
SA + SB Neutral 7
WA + SB Basic 9
WB + SA Acidic 5

5. 1. Titration Curve: Strong Acid and Strong Base
HCl KOH → KCl HOH neutral salt
Indicator pH = 7 Bromothymol Blue- see Ind Chart
50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl
We start here
The pH of 0.10 M HCl is 1.0
The pH of 0.10 M KOH is 13.0 pH
Volume .10 M KOH added 14 7 25 50
0.10 M KOH
0.10 M HCl
Neutral Salt pH = 7.0

6. 2. Titration Curve: Weak Acid and Strong Base
HCN KOH → KCN H2O basic salt
Indicator pH = 9 Phenolphthalein- see ind. chart
20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH
is added to
We end here pH = 3
We start here pH = 14 pH
Volume 1.0 M HCN added 14 7
1.0 M KOH
Basic Salt pH = 9
1.0 M HCN 10 20

7. 3. Titration Curve: Strong Acid and Weak Base
HCl NH3 → NH4+ + Cl- acid salt
Indicator pH = 5 Methyl Red- see ind chart
60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl
1.0 M NH3 pH  10 pH
Volume 1.0 M NH3 added 14 7
Acid Salt pH  5 30 60
1.0 M HCl pH = 0

8. 4. Match the Curve with the ReactionpH
Volume .10 M KOH added 14 7 25 50
A. 3HCl Al(OH)3 → AlCl HOH
B. HCl KOH → KCl + HOH
C. HCN KOH → KCN + HOH

9. 5. Match the Curve with the ReactionpH
Volume 1.0 M NH3 added 14 7 30 60
A. 3HCl Al(OH)3 → AlCl HOH
B. HCl KOH → KCl + HOH
C. HCN KOH → KCN + HOH

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

11. 3 Types of Titrations
Strong acid and strong base Weak acid and strong base Weak base and strong acid

12. Strong acid and Strong base
They produce neutral salts and water.
We have practiced these calculations before.

13. Weak acid and strong base
We expect to produce a basic solution.
Therefore, equivalence point at pH > 7
Indicators around pH = 9; between (8-10)
Rules found through experiments to make your life EASY.

14. Weak acid and strong base

15. Weak acid and strong base
Rules:
pKa = pH ½  means pH when half Volume is used, NOT HALF pH!!!!
Ka = 10 –pKa or Ka = 10-pH ½
Ka = [ H3O+]1/ where [ H3O+]1/2 can be found from pH 1/2
[Acid]equilibrium = [ H3O+]2 … this [H3O+] is found from pH initial
Ka Ka found from above equation
[Acid]original= [Acid]eq + [H3O] from pH initial

16. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of Furoic acid with NaOH.
28.8mL = volume of NaOH required to get to equivalence point
2.021 = initial pH of furoic acid solution
3.170 = pH at 14.4mL point of titration
A) Calculate the Ka value for furoic acid

17. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of Furoic acid with NaOH.
28.8mL = volume of NaOH required to get to equivalence point
2.021 = initial pH of furoic acid solution
3.170 = pH at 14.4mL point of titration
B) Calculate the initial concentration of the furoic acid solution

18. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of Furoic acid with NaOH.
28.8mL = volume of NaOH required to get to equivalence point
2.021 = initial pH of furoic acid solution
3.170 = pH at 14.4mL point of titration
C) Calculate the concentration of the NaOH used.

19. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of Furoic acid with NaOH.
28.8mL = volume of NaOH required to get to equivalence point
2.021 = initial pH of furoic acid solution
3.170 = pH at 14.4mL point of titration
D) Is the titration mixture acidic, basic or neutral at the equivalence point?

20. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of Furoic acid with NaOH.
28.8mL = volume of NaOH required to get to equivalence point
2.021 = initial pH of furoic acid solution
3.170 = pH at 14.4mL point of titration
E) Suggest a suitable indicator for the titration

21. Weak acid and strong base
TRY: The following data was obtained during the titration of 25.0 mL of propanoic acid,
with M NaOH.
Initial pH= 2.950
Volume of NaOH used= 23.8 mL
pH at 11.9 mL = 4.873
A) What is Ka for propanoic acid?

22. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of propanoic acid,
with M NaOH.
Initial pH= 2.950
Volume of NaOH used= 23.8 mL
pH at 11.9 mL = 4.873
B) What is the concentration for propanoic acid based on the [NaOH] and the volumes of the reactants?

23. Weak acid and strong base
The following data was obtained during the titration of 25.0 mL of propanoic acid,
with M NaOH.
Initial pH= 2.950
Volume of NaOH used= 23.8 mL
pH at 11.9 mL = 4.873
C) What is the concentration of propanoic acid as calculated from your value of Ka, found in part,a and the initial pH value?

24. Homework
#129 on page 177