1. Acids and Bases Chapter 16 Acids and Bases

2. Acids and Bases Some Definitions Arrhenius  ________________:Substance that, when dissolved in water, increases the concentration of ________________.

3. Acids and Bases Some Definitions Brønsted–Lowry  Acid:________________  Base:________________

4. Acids and Bases A Brønsted–Lowry acid… …must have a removable (acidic) ________________. A Brønsted–Lowry base… …must have a pair of ________________ electrons.

5. Acids and Bases If it can be either…...it is ________________. HCO 3 - HSO 4 - H2OH2O

6. Acids and Bases What Happens When an Acid Dissolves in Water? Water acts as a Brønsted–Lowry base and abstracts a ________________ (H + ) from the acid. As a result, the ________________of the acid and a ________________ar e formed.

7. Acids and Bases Conjugate Acids and Bases: From the Latin word conjugare, meaning “to join together.” Reactions between acids and bases always yield their conjugate ________________ and ________________.

8. Acids and Bases Acid and Base Strength Strong acids are completely ________________ in water.  Their conjugate bases are quite weak. Weak acids only dissociate ________________ in water.  Their conjugate bases are weak bases.

9. Acids and Bases Acid and Base Strength Substances with negligible acidity do not ________________ in water.  Their conjugate bases are exceedingly strong.

10. Acids and Bases Acid and Base Strength In any acid-base reaction, the ________________ will favor the reaction that moves the ________________ to the stronger ________________. HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) H 2 O is a much stronger base than Cl -, so the equilibrium lies so far to the right K is not measured (K>>1).

11. Acids and Bases Acid and Base Strength Acetate is a stronger base than H 2 O, so the equilibrium favors the left side (K<1). HC 2 H 3 O 2 (aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 - (aq)

12. Acids and Bases Autoionization of Water As we have seen, water is ________________. In pure water, a few molecules act as bases and a few act as acids. This is referred to as ________________. H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq)

13. Acids and Bases Ion-Product Constant The equilibrium expression for this process is K c = [H 3 O + ] [OH - ] This special equilibrium constant is referred to as the ________________for water, K w. At 25°C, K w = 1.0  10 -14

14. Acids and Bases pH pH is defined as the negative base-10 logarithm of the hydronium ion concentration. pH = -log [H 3 O + ]

15. Acids and Bases pH In pure water, K w = [H 3 O + ] [OH - ] = 1.0  10 −-14 Because in pure water [H 3 O + ] = [OH - ], [H 3 O + ] = (1.0  10 -14 ) 1/2 = 1.0  10 -7

16. Acids and Bases pH Therefore, in pure water, pH = -log (1.0  10 -7 ) = 7.00 An ________________ has a higher [H 3 O + ] than pure water, so its pH is <7 A ________________ has a lower [H 3 O + ] than pure water, so its pH is >7.

17. Acids and Bases pH These are the pH values for several common substances.

18. Acids and Bases Other “p” Scales The “p” in pH tells us to take the negative log of the ________________ (in this case, hydrogen ions). Some similar examples are  pOH =−-log [OH - ]  pK w =− -log K w

19. Acids and Bases Watch This! Because [H 3 O + ] [OH - ] = K w = 1.0  10 -14, we know that −-log [H 3 O + ] + -log [OH - ] = -log K w = 14.00 or, in other words, pH + pOH = pK w = 14.00

20. Acids and Bases How Do We Measure pH? For less accurate measurements, one can use  Litmus paper “Red” paper turns blue above ~pH = 8 “Blue” paper turns red below ~pH = 5  An indicator

21. Acids and Bases How Do We Measure pH? For more accurate measurements, one uses a ________________, which measures the voltage in the solution.

22. Acids and Bases Strong Acids You will recall that the seven strong acids are HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 3, and HClO 4. These are, by definition, ________________ ________________ and exist totally as ________________ in aqueous solution. For the monoprotic strong acids, [H 3 O + ] = [acid].

23. Acids and Bases Strong Bases ________________________________ are the soluble hydroxides, which are the alkali metal and heavier alkaline earth metal hydroxides (Ca 2+, Sr 2+, and Ba 2+ ). Again, these substances dissociate completely in ________________ solution.

24. Acids and Bases Dissociation Constants For a generalized acid dissociation, the equilibrium expression would be This equilibrium constant is called the ____________________________, K a. [H 3 O + ] [A - ] [HA] K c = HA (aq) + H 2 O (l) A - (aq) + H 3 O + (aq)

25. Acids and Bases Dissociation Constants The greater the value of K a, the stronger the ________________.

26. Acids and Bases 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 + ] [HCOO - ] [HCOOH] K a =

27. Acids and Bases 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.

28. Acids and Bases Calculating K a from the pH pH = -log [H 3 O + ] 2.38 = -log [H 3 O + ] -2.38 = log [H 3 O + ] 10 −-2.38 = 10 log [H 3 O + ] = [H 3 O + ] 4.2  10 -3 = [H 3 O + ] = [HCOO - ]

29. Acids and Bases 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 +4.2  10 −3 At Equilibrium 0.10 - 4.2  10 -3 = 0.0958 = 0.10 4.2  10 -3

30. Acids and Bases Calculating K a from pH [4.2  10 -3 ] [0.10] K a = = 1.8  10 -4

31. Acids and Bases 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

32. Acids and Bases Calculating Percent Ionization Percent Ionization =  100 4.2  10 -3 0.10 = 4.2%

33. Acids and Bases Calculating pH from K a Calculate the pH of a 0.30 M solution of acetic acid, HC 2 H 3 O 2, at 25°C. HC 2 H 3 O 2 (aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 - (aq) K a for acetic acid at 25°C is 1.8  10 -5.

34. Acids and Bases Calculating pH from K a The equilibrium constant expression is [H 3 O + ] [C 2 H 3 O 2 - ] [HC 2 H 3 O 2 ] K a =

35. Acids and Bases Calculating pH from K a We next set up a table… [C 2 H 3 O 2 ], M[H 3 O + ], M[C 2 H 3 O 2 − ], M Initially0.3000 Change−-x+x+x+x+x At Equilibrium 0.30 − x  0.30 xx We are assuming that x will be very small compared to 0.30 and can, therefore, be ignored.

36. Acids and Bases Calculating pH from K a Now, (x) 2 (0.30) 1.8  10 -5 = (1.8  10 -5 ) (0.30) = x 2 5.4  10 -6 = x 2 2.3  10 -3 = x

37. Acids and Bases Calculating pH from K a pH = −-log [H 3 O + ] pH = −-log (2.3  10 -3 ) pH = 2.64

38. Acids and Bases 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.

39. Acids and Bases Weak Bases Bases react with water to produce ________________.

40. Acids and Bases Weak Bases The equilibrium constant expression for this reaction is [HB] [OH - ] [B − ] K b = where K b is the ____________________________ constant.

41. Acids and Bases Weak Bases K b can be used to find [OH - ] and, through it, pH.

42. Acids and Bases 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)

43. Acids and Bases 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

44. Acids and Bases 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 =

45. Acids and Bases 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

46. Acids and Bases 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.

47. Acids and Bases Reactions of Anions with Water Anions are ________________. As such, they can react with water in a _________________________to form OH - and the conjugate acid: X - (aq) + H 2 O (l) HX (aq) + OH - (aq)

48. Acids and Bases Reactions of Cations with Water Cations with acidic ________________ (like NH 4 + ) will lower the pH of a solution. Most metal ________________ that are hydrated in solution also lower the pH of the solution.

49. Acids and Bases Reactions of Cations with Water Attraction between nonbonding electrons on oxygen and the metal causes a shift of the electron density in water. This makes the O-H bond more ________________ and the water more ________________. Greater charge and smaller size make a cation more ________________.

50. Acids and Bases Effect of Cations and Anions 1.An ________________ 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 ________________ the pH. 3.A cation that is the conjugate acid of a weak base will ________________ the pH.

51. Acids and Bases Effect of Cations and Anions 4.________________ of the strong Arrhenius bases will not affect the pH. 5.Other metal ions will cause a ________________ 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.

52. Acids and Bases Factors Affecting Acid Strength The more ________________ the H-X bond and/or the weaker the H-X bond, the more ________________ the compound. Acidity ________________ from left to right across a row and from top to bottom down a group.

53. Acids and Bases Factors Affecting Acid Strength In oxyacids, in which an OH is bonded to another atom, Y, the more ________________ Y is, the more ________________ the acid.

54. Acids and Bases Factors Affecting Acid Strength For a series of oxyacids, acidity ________________ with the number of oxygens.

55. Acids and Bases Factors Affecting Acid Strength ________________ in the conjugate bases of carboxylic acids stabilizes the base and makes the conjugate acid more acidic.

56. Acids and Bases Lewis Acids Lewis acids are defined as ________________ acceptors. Atoms with an empty ________________ orbital can be Lewis acids.

57. Acids and Bases Lewis Bases Lewis bases are defined as ________________ donors. Anything that could be a Brønsted–Lowry base is a ________________ base. Lewis bases can interact with things other than protons, however.