1. Acids and Bases Chapter 14

2. Classifying Acids Organic acids contain a carboxyl group or -COOH -- HC 2 H 3 O 2 & citric acid. Inorganic acids -- HCl, H 2 SO 4, HNO 3. Oxyacids -- acid proton attached to oxygen– H 3 PO 4. more oxygen the stronger the acid Monoprotic -- HCl & HC 2 H 3 O 2 Diprotic -- H 2 SO 4 Triprotic -- H 3 PO 4

3. Models of Acids and Bases Arrhenius Concept: Acids produce H + in solution, bases produce OH  ion. Brønsted-Lowry: Acids are H + donors, bases are proton acceptors. HCl + H 2 O  Cl  + H 3 O + acid base acid base

4. Bronsted-Lowry Model The Bronsted-Lowry Model is not limited to aqueous solutions like the Arrhenius Model. NH 3(g) + HCl (g) ----> NH 4 Cl (s) This is an acid-base reaction according to Bronsted-Lowry, but not according to Arrhenius!

5. Hydronium Ion Hydronium ion is a hydrated proton -- H + Hydronium ion is a hydrated proton -- H +. H 2 O. The H + ion is simply a proton. It has a very high charge density, so it strongly is attracted to the very electronegative oxygen of the polar water molecule.

6. Conjugate Acid/Base Pairs HA(aq) + H 2 O(l)  H 3 O + (aq) + A  (aq) conj conj conj conj conj conj conj conj acid 1 base 2 acid 2 base 1 conjugate base: everything that remains of the acid molecule after a proton is lost. conjugate acid: formed when the proton is transferred to the base. Which is the stronger base--H 2 O or A - ?

7. HF(aq) + OH-(aq) -> F-(aq) + H 2 O(l) HCl + OH-  Cl- + H2O HCl + OH-  Cl- + H2O HCl + NH 3  Cl- + NH 4 +

8. The relationship of acid strength and conjugate base strength for acid- base reactions.

9. Acid Strength -Its equilibrium position lies far to the right. (HNO 3 ) -Yields a weak conjugate base. (NO 3  ) Strong Acid:

10. Acid Strength (continued) -Its equilibrium lies far to the left. (CH 3 COOH) -Yields a much stronger (water is relatively strong) conjugate base than water. (CH 3 COO  ) Weak Acid:

11. Acid Dissociation Constant (K a ) HA(aq) + H 2 O(l)  H 3 O + (aq) + A  (aq) K a values for common acids are found in Table 14.2 on page 663.

13. HCOOH(aq) + H20 (l)  COOH - (aq) + H30 + (aq) HClO4(aq) + H20 (l)  ClO4- (aq) + H3O+(aq)

14. A strong acid is nearly 100 % ionized, while a weak acid is only slightly ionized.

15. Diagram a represents a strong acid, while b represents a weak acid which remains mostly in the molecular form.

17. Water as an Acid and a Base Water is amphoteric (it can behave either as an acid or a base). H 2 O + H 2 O  H 3 O + + OH  conj conj conj conj acid 1 base 2 acid 2 base 1 acid 1 base 2 acid 2 base 1

18. Ion product Constant, K w K w is called the ion-product constant or dissociation constant. K w = 1  10  14 M 2 at 25°C neutral solution [H + ] = [OH - ] = 1.0 x 10 -7 M acidic solution [H + ] > [OH - ] [H + ] > 1.0 x 10 -7 M basic solution [H + ] 1.0 x 10 -7 M No matter what the concentration of H + or OH - in an aqueous solution, the product, K w, will remain the same for that Temp.

19. [H + ] & [OH - ] Calculations Calculate the [H + ] for a 1.0 x 10 -5 M OH -. K w = [H + ][OH - ] [H + ] = K w /[OH - ] [H + ] = 1.0 x 10 -14 M 2 /1.0 x 10 -5 M [H + ] = [H + ] = 1.0 x 10 -9 M

20. [H + ] & [OH - ] Calculations Continued Calculate the [OH - ] for a 10.0 M H +. K w = [H + ][OH - ] [OH - ] = K w /[H + ] [OH -] = 1.0 x 10 -14 M 2 /10.0 M [OH - ] = [OH - ] = 1.0 x 10 -15 M

21. The pH Scale pH =  log[H + ] pH in water usually ranges from 0 to 14. K w = 1.00  10  14 = [H + ] [OH  ] pK w = 14.00 = pH + pOH As pH rises, pOH falls (sum = 14.00).

22. pH scale and pH values for common substances. A pH of 1 is 100 times more acidic than a pH of 3.

23. Logarithms -log 1.00 x 10 -7 = 7.000 7.000 characteristicmantissa The number of significant digits in 1.00 x 10 -7 is three, therefore, the log has three decimal places. The mantissa represents the log of 1.00 and the characteristic represents the exponent 7.

24. pH & Significant Figures pH in [H + ] # decimal places pH -------> # Significant Figure in [H + ] [H + ] pH # Significant Figures [H + ] -------> # decimal places pH pH = - log [H + ][H + ] = 10 (-pH) [H + ] = 1.0 x 10 -5 MpH = 5.00

25. pH Calculations What is the pOH, [H + ], & [OH - ] for human blood with a pH of 7.41? pH + pOH = 14.00 pOH = 14.00 - pH pOH = 14.00 - 7.41 pOH = 6.59

26. pH Calculations Continued What is the pOH, [H + ], & [OH - ] for human blood with a pH of 7.41? pH = - log [H + ] [H + ] = antilog (-pH) [H + ] = antilog (-7.41) [H + ] = 3.9 x 10 -8 M Note: The number of significant figures in the antilog is equal to the number of decimal places in the pH.

27. pH Calculations Continued What is the pOH, [H + ], & [OH - ] for human blood with a pH of 7.41? pOH = - log [OH - ] [OH - ] = antilog (-pOH) [OH - ] = antilog (-6.59) [OH - ] = 2.6 x 10 -7 M Note: The number of significant figures in the antilog is equal to the number of decimal places in the pOH.

28. Review Book 338-340 1-22

29. pH of Strong Acid Solutions Calculate the pH of a 0.10 M HNO 3 solution. Major species are: H +, NO 3 -, Sources of H + are from HNO 3 and H 2 O -- amount from water is insignificant.  [H + ] = 0.10 M pH = - log [H + ] pH = - log [0.10] pH = - log [0.10] pH = 1.00 pH = 1.00 Note: The number of significant figures in the [H + ] is the same as the decimal places in the pH.

30. A solution is prepared by adding 15.8g of HCl to enough water to make a total volume of 400.ml What is the pH of the solution ?

31. Solving Weak Acid Equilibrium Problems -Write equilibrium expression for dominant equilibrium. -Use an ice table.

32. pH of Weak Acid Solutions Calculate the pH of a 0.100 M HOCl solution. K a HOCl = 3.5 x 10 -8 K a HOCl = 3.5 x 10 -8 Major species: HOCl and HOH  HOCl will be only significant source of [H + ]. K a = 3.5 x 10 -8 = [H + ][OCl - ]/[HOCl]

33. pH of Weak Acid Solutions Continued ICE ICE [HOCl] [OCl - ] [H + ] [HOCl] [OCl - ] [H + ] Initial (mol/L) 0.100 0 0 Change (mol/L) - x + x + x Equil. (mol/L) 0.100 - x 0 + x 0 + x

34. pH of Weak Acid Solutions Continued K a = 3.5 x 10 -8 = [H + ][OCl - ]/[HOCl] 3.5 x 10 -8 = [x][x]/[0.100 - x] K a is more than 100 x smaller than concentration, x can be neglected in the denominator. K a = 3.5 x 10 -8 = [x][x]/[0.100] x 2 = 3.5 x 10 -9 x = 5.9 x 10 -5 M

35. pH of Weak Acid Solutions Continued Approximation check: % dissociation = (x/[HOCl] o ) (100%) % dissociation = (5.9 x 10 -5 /0.100)(100%) % dissociation = 0.059 % This is much less than 5 % and therefore the approximation was valid.

36. Percent Dissociation (Ionization) The percent dissociation calculation is exactly the same as the one to check the 5 % approximation.

37. pH of a weak acid practice Calculate the Ph of a.500M aqueous solution of formic acid,HCOOH (Ka=1.77x10 -4) Rb324

38. pH of a weak acid practice II Calculate the pH of a.200 M HCA Solution with a Ka=7.45x10 -4 Rb324-325

40. Bases Bases are often called alkalis because they often contain alkali or alkaline earth metals. “Strong” and “weak” are used in the same sense for bases as for acids. strong = complete dissociation (hydroxide ion supplied to solution) NaOH(s)  Na + (aq) + OH  (aq)

41. Bases (continued) weak = very little dissociation (or reaction with water) H 3 CNH 2 (aq) + H 2 O(l)  H 3 CNH 3 + (aq) + OH  (aq) K b calculations are identical to K a calculations.

42. Calculate the pH of a solution made by adding 4.63 g of LiOH into water for a total volume of 400 ml Calculate the pH of a.350M solution of CH 3 NH 2 (Kb=4.38x10 -4 )

43. What is the pH of a 0.100 M solution of ammonia (NH 3 ) (K b = 1.8x10 -5 )?

44. Kw =Ka x Kb

45. Calculate the pH of a.500M KF solution at 25dc Kb for = 1.4.0x10 -11 text689

46. pH =8.31

47. pH of a Salt Calculate the pH of a.500M NaNO 2 solution at 25dc (Ka for HNO 2 = 4.0x10 -4 Rb334

48. 8.55

49. Ph of a salt practice acid Calculate the pH of a.010M AlCl 3 solution. Ka Value for Al(H 2 O 6 ) 3+ is 1.4x10 -5

50. Calculate the pH of a.010M NH 4 Cl solution. Kb Value for NH 3 is 5.6x10 -10

51. pH=5.13

52. Polyprotic Acids... can furnish more than one proton (H + ) to the solution.

53. Calculate the pH of a 5.0M H3PO4 solution and the equilibrium concentrations of H 3 PO 4, H 2 PO 4 -, HPO 4 -2, PO 3 -3 Ka 1 = 7.5 x10 -3 Ka 2 = 6.2 x10 -8 Ka 3 = 4.8 x10 -13Rb 331-332