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Catalyst

Catalyst. Cool Acid/Base Reaction. Lecture 7.5 – Acid/Base Titrations. Today’s Learning Targets. LT 7.12 – I can interpret the titration curve for strong acid/base titration and I can calculate the equivalence point and unknown concentrations from titration data. Acid/Base Indicators.

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Catalyst

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  1. Catalyst

  2. Cool Acid/Base Reaction

  3. Lecture 7.5 – Acid/Base Titrations

  4. Today’s Learning Targets • LT 7.12 – I can interpret the titration curve for strong acid/base titration and I can calculate the equivalence point and unknown concentrations from titration data.

  5. Acid/Base Indicators • Indicators– Compounds that change color depending on pH. • Therefore, these compounds tell us the general pH of our solution based their color

  6. Titrations • Often, we have solutions of unknown concentrations • Titration – The controlled addition of solution of known concentration/volume to a solution of known volume, but unknown concentration. • Standard Solution – Solution whose concentration and volume with know precisely

  7. Acid/Base of known volume and concentration. Acid/Base of known volume and unknown concentration with an indicator.

  8. Strong Acid Titrated with Strong Base

  9. Strong Base Titrated with Strong Acid

  10. Equivalence Point • Equivalence Point– The point at which the two solutions used in a titration are present in equal amounts. • We use indicators to spot this point • For strong acid/strong base titrations, it occurs at pH = 7 • Moles of acid = moles of base at this point

  11. Calculating Concentration for Strong Acid/Strong Base Titrations Volume of base that was added in titration Molarity of base Mole Ratio from balanced chemical reaction Volume of unknown acid

  12. Class Example • If it takes 54 mL of 0.1 M NaOH to neutralize 12.5m L of an HCl solution, what is the concentration of the HCl?

  13. Table Talk • If it takes 14.0 mL of 0.051 M KOH to neutralize 22.5 L of an HNO3 solution, what is the concentration of the HNO3?

  14. Stop and Jot • It takes 25.40 mL of 1.1 M HBr to neutralize 32.5 L of an KOH solution, what is the concentration of the HBr?

  15. Weak Acid Titrated with Strong Base • When titrating a weak acid or base with a strong acid or base, the titration curve looks different. • Equivalence point does notoccur at pH = 7 • More on the calculations associated with these next week!

  16. Weak Acid Titrated with Strong Base

  17. Weak Base Titrated with Strong Acid

  18. Fill in the Box • In the grid provided, complete the 9 questions that are around the room. • Complete as many problems as possible.

  19. What is the pH of this base?

  20. Lecture 7.6 – Weak Acid/Base Equilibrium

  21. Today’s Learning Targets • LT 7.14 – I can explain the autoionization of water and utilize this definition to explain the Kw equation. • LT 7.15 – I can write the acid and base dissociation constants for a given weak acid or base.

  22. Woops! I Lied Again  • In an aqueous solution, there is no such thing as H+ • H+ reacts with water to make the hydronium ion, H3O+: • H+ + H2O  H3O+ • Therefore when we say [H+], we mean [H3O+]. You can use either in this class

  23. Autoionization of Water • Water can act as either an acid or a base. It is amphoteric, it can function as either an acid or a base. • Therefore, in a solution of water, we have the equilibrium of: • H2O (l) + H2O (l) H3O+ (aq) + OH- (aq) • We can calculate the equilibrium constant of this reaction to be: • This is a powerful equation because it allows us to interconvert, so it is appreviated as Kw: ⇌

  24. Where pH comes from… • We now know that: • Therefore we can do the following:

  25. Class Example • Calculate the [H+] in a solution of [OH-] = 0.010 M. Calculate the pH of the solution.

  26. Table Talk • Calculate the [OH-] in a solution of [H+] = 2 x 10-6 M. Calculate the pH of the solution.

  27. Weak acids/Ka ⇌ • Recall, a weak acid is partially dissociated. • Therefore, reactants and products are in equilibrium: • HA H+ + A- • The equilibrium constant can be written for all weak acids as: • The equilibrium constant for a weak acid equilibrium is known as the acid dissociation constant (Ka)

  28. Class Example ⇌ • You have a solution of the following acid: • HF (aq) + H2O (l) H3O+ (aq) + F- (aq) • Given that the equilibrium concentrations are [HF] = 0.562 M, [H3O+ ] = 4.5 x 10-2 M, and [F- ] = 8.9 x 10-3 M, calculate the value of Ka.

  29. Table Talk ⇌ • You have a solution of the following acid: • HOC6H5 (aq) + H2O (l) H3O+ (aq) + OC6H5- (aq) • Given that the equilibrium concentrations are [HOC6H5] = 0.062 M, [H3O+ ] = 1.5 x 10-4 M, and [OC6H5- ] = 3.1 x 10-5 M, calculate the value of Ka.

  30. Weak Bases/Kb ⇌ • Just like with weak acids, a weak acid partially dissociates • Therefore, reactants and products are in equilibrium: • B (aq) + H2O (l) HB+ (aq) + OH- (aq) • The equilibrium constant can be written for all weak acids as: • The equilibrium constant for a weak base equilibrium is known as the base dissociation constant (Kb)

  31. Relationship between Ka and Kb ⇌ • Consider the weak acid, NH4+: • NH4+ (aq) NH3 (aq) + H+ (aq) • Additionally, consider the base in the above reaction: • NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq) • The two equilibrium expressions can be written as: ⇌

  32. Relationship between Ka and Kb ⇌ ⇌ • We can add the two equations together to obtain: • NH4+ (aq) NH3 (aq) + H+ (aq) • + NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq) • H2O (l) H+ (aq) + OH- (aq) • When we add two equilibriums together, K is multiplied: ⇌

  33. Class Example • Calculate the Kb for the fluoride ion (Ka = 6.8 x 10-4)

  34. Table Talk • Calculate the Ka for the ammonium ion (Kb = 1.8 x 10-5)

  35. White Board Problems

  36. White Board Problems 1. You have a solution that has [H+] = 0.425 M. What is the [OH-] for the solution? 2. Calculate the [H+] in a solution of [OH-] = 0.05620 M. Calculate the pH of the solution. 3. Write the acid dissociation constant for HF 4. Write the base dissociation constant for NH3 5. Write the acid dissociation constant for HCNO (the first H is acidic). 6. The Ka for benzoic acid is 6.3 x 10-5. What is the value of the Kb for benzoic acid? 7. The Ka for nitrous acid is 4.5 x 10-4. What is the value of the Kb for nitrous acid?

  37. Exit Ticket • You titrate a strong acid with a strong base. Draw what the titration curve looks like in pH vs. Volume of Base Added graph. • You titrate 25.7 mL of of H2SO4with 67.8 mL of 0.678 M of CsOH. What is the molarity of the H2SO4 that was titrated? • You measure the [H+] of a solution to be 0.789 M. What is the pH? What is the [OH-]? • The Kb for pyridine (C5H5N) is 1.7 x 10-9. What is the value of pyridine’s Ka?

  38. Closing Time • Read: 4.6 and 16 • Homework: • Pre – Lab for Lab 12 due at start of class Monday/Tuesday

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