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Logarithms, pH, pOH, pK a. LOGARITHMS LOGARITHMpower to which you must raise a base number to obtain the desired number.

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Presentation on theme: "Logarithms, pH, pOH, pK a. LOGARITHMS LOGARITHMpower to which you must raise a base number to obtain the desired number."— Presentation transcript:

1 Logarithms, pH, pOH, pK a

2 LOGARITHMS LOGARITHMpower to which you must raise a base number to obtain the desired number

3 Log (base 10) Logs (base 10) = exponent to which 10 must be raised to obtain desired number

4 Log (base 10) Logs (base 10) = exponent to which 10 must be raised to obtain desired number log 1 = 0 because 1 = 10 0

5 Log (base 10) Logs (base 10) = exponent to which 10 must be raised to obtain desired number log 1 = 0 because 1 = 10 0 Common log of a number that is a power of 10 is always a whole number

6 Log (base 10) log is exponent of 10 WITH ITS SIGN eg -4 log 10 -4 = -4 Fractional power of 10 on calculator, enter number and use log button, log (2 x 10 -4) = -3.7

7 Inverse log (base 10) Inverse log used to find number corresponding to log = 10 x

8 Inverse log (base 10) Inverse log used to find number corresponding to log = 10 x Whole integer log: use log (given number) with its sign as power of 10

9 Inverse log (base 10) Inverse log used to find number corresponding to log = 10 x Whole integer log: use log (given number) with its sign as power of 10 Decimal log: enter number WITH ITS SIGN Use the:

10 Inverse log (base 10) Inverse log used to find number corresponding to log = 10 x Whole integer log: use log (given number) with its sign as power of 10 Decimal log: enter number WITH ITS SIGN and use either 10 x button OR

11 Inverse log (base 10) Inverse log used to find number corresponding to log = 10 x Whole integer log: use log (given number) with its sign as power of 10 Decimal log: enter number WITH ITS SIGN and use either 10 x button OR [2 nd ][log] buttons

12 Example #1 – inverse log What number corresponds to a log= -5.34?

13 Inverse log –5.34 = 10 -5.34

14 Example #1 Solution [2 nd ]log –5.34 = 10 -5.34 = 4.6 x 10 -6

15 pH

16 A measure of the acidity of aqueous solutions

17 pH A measure of the acidity of aqueous solutions pH= - log [H 3 O + ]

18 pH A measure of the acidity of aqueous solutions pH= - log [H 3 O + ] pOH= - log [OH - ]

19 pH A measure of the acidity of aqueous solutions pH= - log [H 3 O + ] pOH= - log [OH - ] pK= - log [K eq ]

20 pH A measure of the acidity of aqueous solutions pH= - log [H 3 O + ] pOH= - log [OH - ] pK= - log [K eq ] p(anything) = - log (anything)

21 [H 3 O + ] from pH [OH - ] from pOH [H 3 O + ]= 10 - pH

22 [H 3 O + ] from pH [OH - ] from pOH [H 3 O + ]= 10 - pH [OH - ]= 10 - pOH

23 [H 3 O + ] from pH [OH - ] from pOH [H 3 O + ]= 10 - pH [OH - ]= 10 - pOH the higher the pH, the lower the [H 3 O + ] in the solution

24 pH in a NEUTRAL SOLUTION neutral solution: [H 3 O + ] = [OH - ] = 1.0 x 10 -7 M

25 pH in a NEUTRAL SOLUTION neutral solution: [H 3 O + ] = [OH - ] = 1.0 x 10 -7 M pH = pOH = 7.00

26 SUMMARY OF pH pHpOH acidic< 7

27 SUMMARY OF pH pHpOH acidic< 7 neutral 7

28 SUMMARY OF pH pHpOH acidic< 7 neutral 7 basic> 7

29 SUMMARY OF pH pHpOH acidic 7 neutral 7 basic> 7

30 SUMMARY OF pH pHpOH acidic 7 neutral 7 7 basic> 7

31 SUMMARY OF pH pHpOH acidic 7 neutral 7 7 basic> 7< 7

32 pH CHANGE change of 1 pH unit means [H 3 O + ] has undergone a 10-fold change

33 pH CHANGE change of 1 pH unit means [H 3 O + ] has undergone a 10-fold change pH 5 vs pH 6:

34 pH CHANGE change of 1 pH unit means [H 3 O + ] has undergone a 10-fold change pH 5 vs pH 6: change of one pH unit; change [ ] by factor of 10

35 pH CHANGE change of 1 pH unit means [H 3 O + ] has undergone a 10-fold change pH 5 vs pH 6: change of one pH unit; change [ ] by factor of 10 pH 510X more acidic than pH 6

36 pH CHANGE change of 1 pH unit means [H 3 O + ] has undergone a 10-fold change pH 5 vs pH 6: change of one pH unit; change [ ] by factor of 10 pH 510X more acidic than pH 6 pH 4100X more acidic than pH 6

37 pK W K w = [H 3 O + ][OH - ] = 1.0 x 10 -14

38 pK W K w = [H 3 O + ][OH - ] = 1.0 x 10 -14 pH + pOH = 14.00 = pK w

39 pH of STRONG ACID

40 Example #2 Calculations Involving pH and pOH Calculate [H 3 O + ], pH, [OH - ], and pOH for a 0.015 M HNO 3 solution.

41 Example #2 Solution HNO 3 (aq) + H 2 O  H 3 O + (aq) + NO 3 - (aq) 0.015 M 0.015 M

42 Example #2 Solution HNO 3 (aq) + H 2 O  H 3 O + (aq) + NO 3 - (aq) 0.015 M 0.015 M pH = - log [H 3 O + ]

43 Example #2 Solution HNO 3 (aq) + H 2 O  H 3 O + (aq) + NO 3 - (aq) 0.015 M 0.015 M pH = - log [H 3 O + ] = - log 0.015 = - (-1.82) = 1.82

44 Example #2 Solution pH + pOH = 14.00

45 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH

46 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18

47 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18 pOH = - log [OH - ]

48 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18 pOH = - log [OH - ] 12.18 = - log [OH - ]

49 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18 pOH = - log [OH - ] 12.18 = - log [OH - ] [OH - ] = [2 nd ]log -12.18

50 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18 pOH = - log [OH - ] 12.18 = - log [OH - ] [OH - ] = [ 2 nd ] log -12.18 = 10 -12.18

51 Example #2 Solution pH + pOH = 14.00 pOH = 14.00 - pH = 14.00 - 1.82 = 12.18 pOH = - log [OH - ] 12.18 = - log [OH - ] [OH - ] = [2 nd ]log -12.18 =10 -12.18 = 6.7 x 10 -13 M

52 pH of STRONG BASE

53 Example #3 Calculations Involving pH and pOH Calculate [H 3 O + ], pH, [OH - ], and pOH for a 0.015 M Ca(OH) 2 solution.

54 Example #3 Solution Ca(OH) 2 (aq)  Ca 2+ (aq) + 2 OH - (aq)

55 Example #3 Solution Ca(OH) 2 (aq)  Ca 2+ (aq) + 2 OH - (aq) 0.015 M 2 x 0.015 M = 0.030 M

56 Example #3 Solution Ca(OH) 2 (aq)  Ca 2+ (aq) + 2 OH - (aq) 0.015 M 2 x 0.015 M = 0.030 M pOH = - log [OH - ]

57 Example #3 Solution Ca(OH) 2 (aq)  Ca 2+ (aq) + 2 OH - (aq) 0.015 M 2 x 0.015 M = 0.030 M pOH = - log [OH - ] = - log 0.030 = - (-1.52) = 1.52

58 Example #3 Solution pH + pOH = 14.00

59 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH

60 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48

61 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48 pH = - log [H 3 O + ]

62 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48 pH = - log [H 3 O + ] 12.48 = - log [[H 3 O + ]

63 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48 pH = - log [H 3 O + ] 12.48 = - log [[H 3 O + ] [H 3 O + ] = [2 nd ]log -12.48

64 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48 pH = - log [H 3 O + ] 12.48 = - log [[H 3 O + ] [H 3 O + ] = [2 nd ]log -12.48 = 10 -12.48

65 Example #3 Solution pH + pOH = 14.00 pH = 14.00 - pOH = 14.00 - 1.52 = 12.48 pH = - log [H 3 O + ] 12.48 = - log [[H 3 O + ] [H 3 O + ] = [2 nd ]log -12.48 =10 -12.48 =3.3 x 10 -13 M

66 pK a pK a = - log K a

67 pK a pK a = - log K a The lower the pK a, the stronger the acid

68 pK a pK a = - log K a The lower the pK a, the stronger the acid Used with weak acids Strong acid have K a approaching infinity

69 REVIEW Auto-ionization of H 2 O: K w = [H 3 O + ][OH - ] pH = - log [H 3 O + ] = - log [H + ] pOH = - log [OH - ] pK = - log K


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