1. Basic concepts: Acid-Base chemistry & pH 1.Recognizing acid/base and conjugate base/acid 2.Calculation of pH, pOH, [H 3 O + ], [OH - ] 3.Calculating pH for solutions of strong acids/base 4.Ionization constant: K a, K b 5.Polyprotic acid (and associated K a values) 6.pK a, pK b 7.Acid-Base properties of salts 8.Predicting direction of acid-base reaction 9.Types of acid-base reactions 10.Calculations with equilibrium constants

2. © 2009, Prentice-Hall, Inc. Defining Acids & Bases Arrhenius – An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions. – A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions.

3. © 2009, Prentice-Hall, Inc. Some Definitions Brønsted-Lowry – An acid is a proton donor. – A base is a proton acceptor. A Brønsted-Lowry acid… …must have a removable (acidic) proton. A Brønsted-Lowry base… …must have a pair of nonbonding electrons

4. © 2009, Prentice-Hall, Inc. If it can be either… …it is amphiprotic. HCO 3 - HSO 4 - H2OH2O

5. Acids Acids can be: monoprotic: example HC 3 H 3 O 2 Diprotic: example H 2 SO 4 Polyprotic: example H 3 PO 4 ……We’ll talk more about these later.

6. © 2009, Prentice-Hall, Inc. What Happens When an Acid Dissolves in Water? Water acts as a Brønsted-Lowry base and abstracts a proton (H + ) from the acid. As a result, the conjugate base of the acid and a hydronium ion are formed.

7. © 2009, Prentice-Hall, Inc. Conjugate Acids and Bases The term conjugate comes from the Latin word “conjugare,” meaning “to join together.” Reactions between acids and bases always yield their conjugate bases and acids.

8. Strong acids and bases almost completely ionize in water (~100%): K strong >> 1 (product favored) Weak acids and bases ionize in water to only a small extent (<<100%): K weak << 1 (Reactant favored) Equilibrium Constants for Acids & Bases

9. ionization constant The relative strength of an acid or base can also be expressed quantitatively with an equilibrium constant, often called an ionization constant. For the general acid HA, we can write: ConjugateacidConjugatebase Equilibrium Constants for Acids & Bases

10. © 2009, Prentice-Hall, Inc. Dissociation Constants The greater the value of K a, the stronger is the acid.

11. ionization constant The relative strength of an acid or base can also be expressed quantitatively with an equilibrium constant, often called an ionization constant. For the general base B, we can write: ConjugatebaseConjugateAcid Equilibrium Constants for Acids & Bases

12. © 2009, Prentice-Hall, Inc. Weak Bases Bases react with water to produce hydroxide ion.

13. © 2009, Prentice-Hall, Inc. Weak Bases K b can be used to find [OH - ] and, through it, pH.

14. © 2009, Prentice-Hall, Inc. Acid and Base Strength Strong acids are completely dissociated in water. – Their conjugate bases are quite weak. Weak acids only dissociate partially in water. – Their conjugate bases are weak bases.

15. © 2009, Prentice-Hall, Inc. K a and K b K a and K b are related in this way: K a  K b = K w Therefore, if you know one of them, you can calculate the other.

16. Acids ConjugateBases Increase strength Ionization Constants for Acids/Bases

17. © 2009, Prentice-Hall, Inc. Polyprotic Acids… …have more than one acidic proton If the difference between the K a for the first dissociation and subsequent K a values is 10 3 or more, the pH generally depends only on the first dissociation.

18. Logarithmic Scale of Relative Acid Strength, pK a Many chemists use a logarithmic scale to report and compare relative acid strengths. pK a =  log(K a ) The lower the pK a, the stronger the acid. AcidHCO 3  HClOHF pK a 10.327.463.14 Equilibrium Constants for Acids & Bases

19. © 2009, Prentice-Hall, Inc. Calculating K a from the pH The pH of a 0.10 M solution of formic acid, HCOOH, at 25  C is 2.38. Calculate K a for formic acid at this temperature. We know that [H 3 O + ] [COO - ] [HCOOH] K a =

20. © 2009, Prentice-Hall, Inc. Calculating K a from the pH The pH of a 0.10 M solution of formic acid, HCOOH, at 25  C is 2.38. Calculate K a for formic acid at this temperature. To calculate K a, we need the equilibrium concentrations of all three things. We can find [H 3 O + ], which is the same as [HCOO - ], from the pH.

21. © 2009, Prentice-Hall, Inc. Calculating K a from pH Now we can set up a table… [HCOOH], M[H 3 O + ], M[HCOO - ], M Initially0.1000 Change - 4.2  10 -3 + 4.2  10 -3 At Equilibrium 0.10 - 4.2  10 -3 = 0.0958 = 0.10 4.2  10 -3

22. © 2009, Prentice-Hall, Inc. Calculating K a from pH [4.2  10 -3 ] [0.10] K a = = 1.8  10 -4

23. © 2009, Prentice-Hall, Inc. Calculating Percent Ionization Percent Ionization =  100 In this example [H 3 O + ] eq = 4.2  10 -3 M [HCOOH] initial = 0.10 M [H 3 O + ] eq [HA] initial Percent Ionization =  100 4.2  10 -3 0.10 = 4.2%

24. Calculating K a from experimental data such as pH: The pH of a 0.100M solution of propanioic acid (CH 3 CH 2 CO 2 H) is 2.94. What is the value of Ka for propanoic acid? 1.Write the ionization equation for this weak acid 2.Determine the equilibrium expression 3.Based on pH, determine the [H 3 O + ] 4.Develop an ICE chart.

25. Use the equilibrium constant to determine the pH of a solution containing a weak acid or base. What is the pH of 0.050M CH 3 COOH? Ka = 1.8x10-5 1.Establish equation for ionization of CH3COOH 2.Set up an ICE chart 3.Determine equilibrium concentrations of [H3O+] 4.Calculation pH

26. © 2009, Prentice-Hall, Inc. pH of Basic Solutions What is the pH of a 0.15 M solution of NH 3 ? [NH 4 + ] [OH - ] [NH 3 ] K b = = 1.8  10 -5 NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq)

27. © 2009, Prentice-Hall, Inc. pH of Basic Solutions Tabulate the data. [NH 3 ], M[NH 4 + ], M[OH - ], M Initially0.1500 At Equilibrium 0.15 - x  0.15 xx

28. © 2009, Prentice-Hall, Inc. pH of Basic Solutions (1.8  10 -5 ) (0.15) = x 2 2.7  10 -6 = x 2 1.6  10 -3 = x 2 (x) 2 (0.15) 1.8  10 -5 =

29. © 2009, Prentice-Hall, Inc. pH of Basic Solutions Therefore, [OH - ] = 1.6  10 -3 M pOH = -log (1.6  10 -3 ) pOH = 2.80 pH = 14.00 - 2.80 pH = 11.20

30. © 2009, Prentice-Hall, Inc. Effect of Cations and Anions 1.An anion that is the conjugate base of a strong acid will not affect the pH. 2.An anion that is the conjugate base of a weak acid will increase the pH. 3.A cation that is the conjugate acid of a weak base will decrease the pH.

31. © 2009, Prentice-Hall, Inc. Effect of Cations and Anions 4.Cations of the strong Arrhenius bases will not affect the pH. 5.Other metal ions will cause a decrease in pH. 6.When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base, the affect on pH depends on the K a and K b values.

32. Anions that are conjugate bases of strong acids (for examples, Cl  or NO 3 . These species are such weak bases that they have no effect on solution pH. Acid–Base Properties of Salts

33. Anions such as CO 3 2  that are the conjugate bases of weak acids will raise the pH of a solution. Hydroxide ions are produced via “Hydrolysis”. Acid–Base Properties of Salts

34. Alkali metal and alkaline earth cations have no measurable effect on solution pH. Since these cations are conjugate acids of strong bases, hydrolysis does not occur. Acid–Base Properties of Salts

35. Basic cations are conjugate bases of acidic cations such as [Al(H 2 O) 6 ] 3+. Acidic cations fall into two categories: (a) metal cations with 2 + and 3 + charges and (b) ammonium ions (and their organic derivatives). All metal cations are hydrated in water, forming ions such as [M(H 2 O) 6 ] n+. Acid–Base Properties of Salts

36. Acid – Base Properties of Ions in a water Solution Decide effect of the cation on pH. Decide effect of the anion on pH. Combine the effect of the two Ka>Kb =acidic, Kb>Ka = basic) SpectatorBasicAcidic Anion Cl - NO 3 - Br - ClO 4 - I - (anion of strong acids) C 2 H 3 O 2 - F - CO 3 2- PO 4 3- (CB of weak acid) CationLi + Ca + Na + Sr 2+ K + Ba 2+ (cation of strong base) NH 4 + Mg 2+ Al 3+ Transition metal ions (CA of weak base)

37. Acid–Base Properties of Salts: Practice

39. 3. Acid-base properties of salts of a weak acid or weak base: Identify if the following ions contribute toward an aqueous solution being acid, basic or neutral. If acidic or basic, write a net ionic equation to explain the behavior: 1.NO 3 - 2. PO 4 3- 3. HCO 3 -

40. pH calculation of a salt solution What is the pH of a 0.10M solution of NH 4 Cl? The K b of NH 3 = 1.8x10 5- 1.Identify equilibrium equation. 2.Identify dissociation constant 3.Develop an ICE chart 4.Complete calculations 5.Determine pH from [H 3 O+]

41. According to the Brønsted–Lowry theory, all acid–base reactions can be written as equilibria involving the acid and base and their conjugates. All proton transfer reactions proceed from the stronger acid and base to the weaker acid and base. Predicting the Direction of Acid–Base Reactions

42. When a weak acid is in solution, the products are a stronger conjugate acid and base. Therefore equilibrium lies to the left. All proton transfer reactions proceed from the stronger acid and base to the weaker acid and base. Predicting the Direction of Acid–Base Reactions

43. Strong acid (HCl) + Strong base (NaOH) Net ionic equation Mixing equal molar quantities of a strong acid and strong base produces a neutral solution. Types Acids–Base Reactions

44. Weak acid (HCN) + Strong base (NaOH) Mixing equal amounts (moles) of a strong base and a weak acid produces a salt whose anion is the conjugate base of the weak acid. The solution is basic, with the pH depending on K b for the anion. Types Acids–Base Reactions

45. Weak acid: Strong Base Calculate the pH of solution prepared by mixing 100mL of O.1M HC 2 H 3 O 2 + 0.1M NaOH. (step one) HC 2 H 3 O 2 + NaOH  Na+(aq) + C 2 H 3 O 2 - (aq) + H 2 O(l) (step two) C 2 H 3 O 2 - (aq) + H 2 O(l) ↔ HC 2 H 3 O 2 (aq) + OH - (aq)

46. Strong acid (HCl) + Weak base (NH 3 ) Mixing equal amounts (moles) of a weak base and a strong acid produces a conjugate acid of the weak base. The solution is basic, with the pH depending on K a for the acid. Types Acids–Base Reactions

47. Weak acid (CH 3 CO 2 H) + Weak base (NH 3 ) Mixing equal amounts (moles) of a weak acid and a weak base produces a salt whose cation is the conjugate acid of the weak base and whose anion is the conjugate base of the weak acid. The solution pH depends on the relative K a and K b values. Types Acids–Base Reactions

48. pH Stoichiometry Problem: Calculate the pH for the following reaction: 1.50 ml of 0.10M Nitric acid is combined with 50 ml of 0.15M Barium Hydroxide. 2.50mL of 1.25M acetic acid is mixed with 50 ml of 2.0M sodium hydroxide.

49. © 2009, Prentice-Hall, Inc. Lewis Acids Lewis acids are defined as electron-pair acceptors. Atoms with an empty valence orbital can be Lewis acids. Lewis structure-central atom is missing a pair of electrons Example: metal cations, non-metal oxides-CO 2

50. © 2009, Prentice-Hall, Inc. Lewis Bases Lewis bases are defined as electron-pair donors. Anything that could be a Brønsted-Lowry base is a Lewis base. Lewis bases can interact with things other than protons, however. Lewis dot structure exhibits lone pair electrons on central atom. Example: NH 3, H 2 O

51. Lewis Acid/Base General equation for a Lewis acid-base reaction: A (acid) + B: (base)  B  A (adduct) The A-B adduct is called a coordinate covalent bond. ex: formation of the hydronium ion (H 3 O + ), H + = Lewis Acid H 2 O = Lewis Base H 3 O + = Adduct

52. p. 794

53. Properties of Acid-Base behavior Trends for Binary Acids (H-X) – Atomic radius – Electronegativity – Both factors impact bond strength (remember strong acids give up H+ so acid strength increases when bond strength decreases) Trends for Oxy-Acids (H-O-X) – Electronegativity (Increase X-O bond increases acid strength) – Number of oxygen atoms (resonance)

54. p. 792

55. Fig. 17-11, p. 792 Unique adduct compounds involving transition metals. Generally characterized by their colors.

56. Example: Coordinate complexes Unique adduct compounds involving transition metals. Generally characterized by their colors.