2. Titration Curve
Plotting the pH of the solution being analyzed as a function of the amount of titrant added.
Equivalence (Stoichiometric) Point – point in the titration when enough titrant has been added to react exactly with the substance in solution being titrated.
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3. Neutralization of a Strong Acid with a Strong Base
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4. The pH Curve for the Titration of 50. 0 mL of 0. 200 M HNO3 with 0
The pH Curve for the Titration of 50.0 mL of M HNO3 with M NaOH
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5. The pH Curve for the Titration of 100. 0 mL of 0. 50 M NaOH with 1
The pH Curve for the Titration of mL of 0.50 M NaOH with 1.0 M HCI
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6. Weak Acid–Strong Base Titration
Step 1: A stoichiometry problem (reaction is assumed to run to completion) then determine concentration of acid remaining and conjugate base formed. Step 2: An equilibrium problem (determine position of weak acid equilibrium and calculate pH).
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7. CONCEPT CHECK!
Consider a solution made by mixing 0.10 mol of HCN (Ka = 6.2 × 10–10) with mol NaOH in 1.0 L of aqueous solution. What are the major species immediately upon mixing (that is, before a reaction)?
Major Species: HCN, Na+, OH-, H2O.
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8. Let’s Think About It… Why isn’t NaOH a major species?
Why aren’t H+ and CN– major species?
List all possibilities for the dominant reaction.
NaOH is a strong base and completely dissociates. HCN is a weak acid and does not dissociate very much.
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9. Let’s Think About It… The possibilities for the dominant reaction are:
H2O(l) + H2O(l) H3O+(aq) + OH–(aq)
HCN(aq) + H2O(l) H3O+(aq) + CN–(aq)
HCN(aq) + OH–(aq) CN–(aq) + H2O(l)
Na+(aq) + OH–(aq) NaOH
Na+(aq) + H2O(l) NaOH + H+(aq)
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10. Let’s Think About It… How do we decide which reaction controls the pH?
H2O(l) + H2O(l) H3O+(aq) + OH–(aq)
HCN(aq) + H2O(l) H3O+(aq) + CN–(aq)
HCN(aq) + OH–(aq) CN–(aq) + H2O(l)
In general, the best acid (HCN in this case) will tend to react with the best base (OH- will always be the best base, if present). Discuss how to calculate the K value for this reaction (note -- it is not a Ka or Kb expression). In this case, K = Ka / Kw = 62,000. We can assume the reaction goes to completion. In this problem, OH- is limiting.

11. Let’s Think About It… HCN(aq) + OH–(aq) CN–(aq) + H2O(l)
What are the major species after this reaction occurs?
After the reaction takes place, the major species are: HCN, CN-, H2O, Na+
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12. Let’s Think About It… Now you can treat this situation as before.
List the possibilities for the dominant reaction.
Determine which controls the pH.
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13. CONCEPT CHECK!
Calculate the pH of a solution made by mixing 0.20 mol HC2H3O2 (Ka = 1.8 × 10–5) with mol NaOH in 1.0 L of aqueous solution.
Major Species: HC2H3O2, Na+, OH-, H2O
Possibilities for reactions:
1) HC2H3O2(aq) + H2O  H3O+(aq) + C2H3O2-(aq)
2) H2O + H2O  H3O+(aq) + OH-(aq)
3) HC2H3O2(aq) + OH-(aq)  H2O + C2H3O2-(aq)
Reaction 3 is most likely. In general, the best acid (HC2H3O2 in this case) will tend to react with the best base (OH- will always be the best base, if present). Discuss how to calculate the K value for this reaction (note -- it is not a Ka or Kb expression). In this case, K = Ka/ Kw = 1.8 x 109. We can assume the reaction goes to completion. In this problem, OH- is limiting.
After the reaction takes place, the major species are: HC2H3O2, C2H3O2-, H2O, Na+
The primary reaction could be:
3) C2H3O2-(aq) + H2O  HC2H3O2(aq) + OH-(aq)
We will see that reactions 1 and 3 will give us the same answer (as long as "x" is negligible in calculations, or solved for exactly). In this case, though, Ka (reaction 1) is greater than Kb (reaction 3) and should be used. When students solve this, make sure they include the initial concentration of the conjugate base (they tend to forget and call it zero).
pH = 3.99
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14. Let’s Think About It… What are the major species in solution?
Why isn’t NaOH a major species?
Why aren’t H+ and C2H3O2– major species?
NaOH is a strong base and completely dissociates. HC2H3O2 is a weak acid and does not dissociate very much.
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15. Let’s Think About It…
What are the possibilities for the dominant reaction?
H2O(l) + H2O(l) H3O+(aq) + OH–(aq)
HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2–(aq)
HC2H3O2(aq) + OH–(aq) C2H3O2–(aq) + H2O(l)
Na+(aq) + OH–(aq) NaOH(aq)
Na+(aq) + H2O(l) NaOH + H+(aq)
Which of these reactions really occur?
See Slide 12.
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16. Let’s Think About It… Which reaction controls the pH?
H2O(l) + H2O(l) H3O+(aq) + OH–(aq)
HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2–(aq)
HC2H3O2(aq) + OH–(aq) C2H3O2–(aq) + H2O(l)
How do you know?
See Slide 12.
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17. Let’s Think About It… K = 1.8 × 109 HC2H3O2(aq) + OH– C2H3O2–(aq)
Before
0.20 mol mol
Change
–0.030 mol –0.030 mol
mol
After
0.17 mol
0.030 mol
K = 1.8 × 109
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18. Steps Toward Solving for pH
HC2H3O2(aq) +
H2O
H3O+
+ C2H3O2-(aq)
Initial
0.170 M ~0
0.030 M
Change –x +x
Equilibrium
0.170 – x x x
Ka = 1.8 × 10–5
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19. EXERCISE!
Calculate the pH of a mL solution of M acetic acid (HC2H3O2), which has a Ka value of 1.8 × 10–5.
pH = 2.87
pH = 2.87
Major Species: HC2H3O2, H2O
Dominant reaction: HC2H3O2(aq) + H2O  H3O+(aq) + C2H3O2-(aq)
The mL is not necessary to know for this problem.
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20. CONCEPT CHECK!
Calculate the pH of a solution made by mixing mL of a M solution of acetic acid (HC2H3O2), which has a Ka value of 1.8 × 10–5, and 50.0 mL of a 0.10 M NaOH solution.
pH = 4.74
Major Species: HC2H3O2, Na+, OH-, H2O
Dominant reaction: HC2H3O2(aq) + OH-(aq)  H2O + C2H3O2-(aq)
In general, the best acid (HC2H3O2 in this case) will tend to react with the best base (OH- will always be the best base, if present). Discuss how to calculate the K value for this reaction (note -- it is not a Ka or Kb expression). In this case, K = Ka/Kw = 1.8 x 109. We can assume the reaction goes to completion. In this problem, OH- is limiting.
After the reaction takes place, the major species are: HC2H3O2, C2H3O2-, H2O
Primary reaction is: HC2H3O2(aq) + H2O  H3O+(aq) + C2H3O2-(aq)
When students solve this, make sure they include the initial concentration of the conjugate base (they tend to forget and call it zero).
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21. CONCEPT CHECK!
Calculate the pH of a solution at the equivalence point when mL of a M solution of acetic acid (HC2H3O2), which has a Ka value of 1.8 × 10–5, is titrated with a 0.10 M NaOH solution.
pH = 8.72
Major Species: HC2H3O2, Na+, OH-, H2O
Dominant reaction: HC2H3O2(aq) + OH-(aq)  H2O + C2H3O2-(aq)
In general, the best acid (HC2H3O2 in this case) will tend to react with the best base (OH- will always be the best base, if present).
At the equivalence point, there are the same number of moles of HC2H3O2(aq) + OH-(aq) to exactly react due to the 1:1 ratio in the balanced equation. This turns out to be mol of both the acid and base in this case. This means that mL of NaOH had to be added.
After the reaction takes place, the major species are: C2H3O2-, H2O, Na+
Primary reaction is: C2H3O2-(aq) + H2O  OH-(aq) + HC2H3O2(aq)
Now use an ICE chart to determine the equilibrium concentrations and finally the pH. Take note that the initial concentration of C2H3O2-(aq) is M (0.010 mol / L).
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22. The pH Curve for the Titration of 50. 0 mL of 0. 100 M HC2H3O2 with 0
The pH Curve for the Titration of 50.0 mL of M HC2H3O2 with M NaOH
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23. The pH Curves for the Titrations of 50. 0-mL Samples of 0
The pH Curves for the Titrations of 50.0-mL Samples of 0.10 M Acids with Various Ka Values with 0.10 M NaOH
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24. The pH Curve for the Titration of 100. 0 mL of 0. 050 M NH3 with 0
The pH Curve for the Titration of mL of M NH3 with 0.10 M HCl
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25. Marks the end point of a titration by changing color.
The equivalence point is not necessarily the same as the end point (but they are ideally as close as possible).
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26. The Acid and Base Forms of the Indicator Phenolphthalein
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27. The Methyl Orange Indicator is Yellow in Basic Solution and Red in Acidic Solution
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28. Useful pH Ranges for Several Common Indicators
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