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Titration

Titration. Titration of a Strong Acid by a Strong Base. Consider what happens to the pH of 25 mL of 0.2 M HCl as it is titrated with 25 mL of 0.2 M NaOH . This result is shown in the diagram to the right. The diagram is referred to as a ___________________ _____________.

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Titration

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  1. Titration

  2. Titration of a Strong Acid by a Strong Base Consider what happens to the pH of 25 mL of 0.2 M HCl as it is titrated with 25 mL of 0.2 M NaOH. This result is shown in the diagram to the right. The diagram is referred to as a ___________________ _____________. As you add base, [H+] ____________ and pH ___________ until what happens?

  3. Titration of a Strong Acid by a Strong Base Ex #1: The following quantities of 0.100 M NaOH have been added to 50.0 mL of 0.100 M HCl. Calculate the pH of the resulting solutions. 49.00 mL 50.00 mL 50.10 mL 51.00 mL

  4. Titration of a Strong Acid by a Strong Base Ex #1: The following quantities of 0.100 M NaOH have been added to 50.0 mL of 0.100 M HCl. Calculate the pH of the resulting solutions. 49.00 mL 50.00 mL 50.10 mL 51.00 mL Because the pH change for strong/strong titrations is large near the equivalence point, the indicator need not change color at exactly pH = 7. Phenolphthalein is often the choice for strong/strong titrations. Its color change occurs during a pH change of 8.3 to 10, but just a slight excess (a few drops) of the titrant will cause this change.

  5. Titration of a Weak Acid with a Strong Base Consider the titration of acetic acid with sodium hydroxide. HC2H3O2+ Na+ + OH- Na+ + C2H3O2- + H2O Calculating the pH of the weak acid depends on where you are in the titration process. Titration Process Before the titration starts Before the equivalence point is reached At the equivalence point After the equivalence point has been reached NaOH HC2H3O2

  6. Titration of a Weak Acid with a Strong Base Consider the titration of acetic acid with sodium hydroxide. Calculating the pH of the weak acid depends on where you are in the titration process. Titration Process Before the titration starts NaOH Initially, we just consider the acetic acid before any base is added. To calculate the pH, follow the same process as calculating the pH of a weak acid. HC2H3O2 HC2H3O2↔C2H3O2- + H2O

  7. Titration of a Weak Acid with a Strong Base Consider the titration of acetic acid with sodium hydroxide. Calculating the pH of the weak acid depends on where you are in the titration process. Titration Process 2) Before the equivalence point is reached NaOH Think about what species are present so that we approach the problem from the correct perspective. The equation shows that since both HC2H3O2 and C2H3O2-- are present, this becomes a _______ problem. HC2H3O2 HC2H3O2↔ C2H3O2- + H2O

  8. Titration of a Weak Acid with a Strong Base Consider the titration of acetic acid with sodium hydroxide. Calculating the pH of the weak acid depends on where you are in the titration process. Titration Process 3) At the equivalence point NaOH At the equivalence point, for a strong acid with a strong base, the pH = ______. This is not the case for a weak acid problem. Why? HC2H3O2 HC2H3O2+ Na+ + OH- Na+ + C2H3O2- + H2O

  9. Titration of a Weak Acid with a Strong Base Consider the titration of acetic acid with sodium hydroxide. Calculating the pH of the weak acid depends on where you are in the titration process. Titration Process After the equivalence point has been reached NaOH After the equivalence point has been reached, the additional OH-- has nothing left to react with so the pH is determined by __________________________________. HC2H3O2

  10. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. Since the molarities are equal and the acid is monoprotic, we will need _______ mL of NaOH to reach the equivalence point. Why is it important to realize this before we begin the problem? 25

  11. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration?

  12. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? Initially, we just consider the acetic acid before any base is added. To calculate the pH, follow the same process as calculating the pH of a weak acid.

  13. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  14. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  15. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  16. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  17. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  18. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  19. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  20. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  21. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  22. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  23. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  24. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  25. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  26. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  27. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  28. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  29. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 1) What is the pH before titration? HC2H3O2↔ H+ + C2H3O2-

  30. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 2) What is the pH after 10.00 mL of the base has been added? Think about what species are present so that we approach the problem from the correct perspective. The equation shows that since both HC2H3O2 and C2H3O2-- are present, this becomes a _______ problem. HC2H3O2↔ C2H3O2- + H2O

  31. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 2) What is the pH after 10.00 mL of the base has been added? HC2H3O2 + OH- C2H3O2- + H2O Use moles in this chart! Convert to M (divide by 35 x 10-3L) HC2H3O2↔ C2H3O2- + H2O

  32. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. 3) What is the pH when 25 mL of the base is added? At the equivalence point, for a strong acid with a strong base, the pH = ______. This is not the case for a weak acid problem. Why? HC2H3O2+ Na+ + OH- Na+ + C2H3O2- + H2O

  33. Titration of a Weak Acid with a Strong Base Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M NaOH. What is the pH after 26 mL of NaOH has been added? After the equivalence point has been reached, the additional OH-- has nothing left to react with so the pH is determined by ______________________________. 25mL reacts, 1mL of NaOH left

  34. Conclusions for Titrations of Weak Acids The pH of a weak acid is ___________ initially than a strong acid of the same concentration because The pH rises rapidly in the early part of a titration, but more slowly near the _____________ ________ because The pH at the equivalence point is not _________ because

  35. Titration of a Weak Acid with a Strong Base The titration curve for a weak acid with a strong base is similar to the curve for a strong acid with a strong base. Construct a titration curve for this problem and compare it to the curve for a strong/strong titration. NaOH HC2H3O2

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