acids and bases

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acids and bases

  1. 1. Chap 15 Acids and Bases Key components <ul><li>Bronsted-Lowery Acids and Bases </li></ul><ul><li>Conjugate Acid-Base Pairs </li></ul><ul><li>pH Scale </li></ul><ul><li>Strong and Weak Acids and Bases </li></ul><ul><li>K a , K b , and K w </li></ul><ul><li>Salt Solutions </li></ul><ul><li>Lewis Acids and Bases </li></ul><ul><li>Lab: Indicators and Titration Curve. </li></ul>
  2. 2. What are acids? What are bases? <ul><li>Acids: A solution which contains more H + than OH - . </li></ul><ul><li>Base: A solution which contains more OH - than H + . </li></ul>
  3. 3. Write the Equilibrium Equation for ionization of water. <ul><li>Write the equilibrium expression for this ionization. </li></ul><ul><li>Is pure water a good conductor electricity? Why? </li></ul><ul><li>In a given moment ionization take place at a rate of 1 out of 8 hundred million molecules. Then what? Autoionization </li></ul>
  4. 4. Water is excluded in the equilibrium expression for aqueous solutions. <ul><li>New Constant is formed because of this. </li></ul><ul><li>K w = ion product constant </li></ul><ul><li>K w = [H + ][OH - ] </li></ul><ul><li>K w = [H + ][OH - ] = 1.0 x10 -14 </li></ul><ul><ul><li>Memorize this expression </li></ul></ul>
  5. 5. Thus: <ul><li>Acid: greater [H + ] </li></ul><ul><li>Base: greater [OH - ] </li></ul><ul><li>Neutral: [H + ] = [OH - ] </li></ul><ul><li>Go to overhead 1 </li></ul>
  6. 6. The Proton in Water <ul><li>H 3 O + Hydronium ion </li></ul><ul><li>H + Hydrogen ion </li></ul><ul><li>on board notes 5 </li></ul>
  7. 7. Practice Problems Chapter 15 Page 641-644 <ul><li>Bronsted-Lowery (4,6,8) </li></ul><ul><li>Dissociation of water (10) </li></ul><ul><li>pH Scale (16-26 Even) </li></ul><ul><li>Weak acids/Weak bases (32,34,36) </li></ul><ul><li>K a and K b (42,44,46,48,52,54) </li></ul><ul><li>Diprotic and Polyprotic Acids (60,62) </li></ul><ul><li>Structure and Strength (66,68) </li></ul><ul><li>Acid-Base Properties for Salts (76,78,79) </li></ul><ul><li>Oxides and hydroxides (84,86) </li></ul><ul><li>Lewis Acid and Bases (90,92) </li></ul>
  8. 8. Bronsted -Lowery Acids and Bases. <ul><li>Acid: a substance capable of donating a proton. </li></ul><ul><li>Base: a substance capable of accepting a proton. </li></ul><ul><li>HCl + H 2 O  H 3 O + + Cl - </li></ul><ul><ul><li>Who is the acid, who is the base? </li></ul></ul>
  9. 9. NH 3 + HCl  NH 4 + + Cl - -Who is the acid, who is the base? <ul><li>NH 3 + H 2 O  NH 4 + + OH - </li></ul><ul><ul><li>Who is the acid, who is the base? </li></ul></ul>
  10. 10. Conjugate Acid-Base Pairs <ul><li>Conjugate: Joined together as a pair. </li></ul><ul><li>In any acid-base reaction, we can tie together the conjugate acid base pairs. </li></ul><ul><ul><ul><ul><ul><li>Overhead 3-6 </li></ul></ul></ul></ul></ul>
  11. 11. <ul><li>Amphoteric: A substance that is capable of acting as either acid or a base. </li></ul><ul><ul><ul><ul><ul><li>whiteboard </li></ul></ul></ul></ul></ul>
  12. 12. Conjugate Acid Base Strength <ul><li>The more easily a substance gives up a proton, the more difficult it is for that conjugate base to accept that proton. </li></ul><ul><ul><li>The stronger the acid the weaker the conjugate base. </li></ul></ul>
  13. 13. <ul><li>The more easily a base accepts a proton, the less readily its conjugate acid gives up a proton. </li></ul><ul><ul><li>The weaker the acid the stronger its conjugate base. </li></ul></ul><ul><ul><li>Overhead 7-8 </li></ul></ul>
  14. 14. The pH Scale <ul><li>pH = power hydrogen ion </li></ul><ul><li>Based on a negative logarithm with a base of 10. </li></ul><ul><li>It is only negative so that the pH turns out positive. </li></ul>
  15. 15. Logarithms <ul><li>Logarithm = the exponent 10 was raised to to achieve the number. </li></ul><ul><ul><ul><li>log10 = 1 (10 1 ) </li></ul></ul></ul><ul><ul><ul><li>log 100 = 2 (10 2 ) </li></ul></ul></ul><ul><ul><ul><li>log 49.23 = (10 1.692229836 ) </li></ul></ul></ul>
  16. 16. Antilogarithm <ul><li>Reverse of log process. </li></ul><ul><li>Antilogarithm= The number that corresponds to what 10 was raised to. </li></ul><ul><ul><ul><li>Antilog 1= 10 </li></ul></ul></ul><ul><ul><ul><li>Antilog 2= 100 </li></ul></ul></ul><ul><ul><ul><li>Antilog 1.69 = 49.23 </li></ul></ul></ul>
  17. 17. pH <ul><li>pH = -log[H + ] </li></ul><ul><li>What is the pH of neutral solution? </li></ul><ul><li>pH = -log(1.0x10 -7 ) =-(-7.00) </li></ul><ul><li>Answer is 7 (just plug log in and remember to change from a neg to a positive). </li></ul>
  18. 18. [H+] = 1.0 x 10 -3 : What is the pH? <ul><li>pH= -log(1.0 x 10 -3 ) = -(-3.00) = 3.00 </li></ul><ul><li>What is the pH of a solution in which [OH - ] = 2.0 x 10 -3 ? </li></ul><ul><li>[H + ] = K w /[OH - ] = 5.0 x 10 -12 </li></ul><ul><li>pH = -log(5.0 x 10 -12 ) = 11.30 </li></ul>
  19. 19. How do you find the hydrogen ion concentration when given the pH? <ul><li>To obtain the [H + ] when given pH, we must take the antilog of a -pH. </li></ul><ul><li>What is [H + ] if the pH is 3.80? </li></ul><ul><li>pH= -log[H + ] = 3.80 </li></ul><ul><li>log[H + ] = -3.80 (mult both sides by a neg 1) </li></ul><ul><li>[H + ] = antilog(-pH) antilong(-3.8) </li></ul>
  20. 20. <ul><li>[H + ] = antilog(-3.8) =10 -3.80 </li></ul><ul><li>10 -3.80 = 1.6 x 10 -4 M </li></ul><ul><li>Review </li></ul><ul><li>[H + ] = antilog(-pH) </li></ul><ul><li>pH = -log[H + ] </li></ul>
  21. 21. pOH <ul><li>pOH = -log[OH - ] </li></ul><ul><li>pH + pOH = -log K w =14 </li></ul><ul><ul><li>Thus pH + pOH = 14 </li></ul></ul>
  22. 22. Strong Acids and Strong bases <ul><li>Strong electrolytes: Solute that completely ionizes in solution and conducts electricity </li></ul><ul><li>Acids: HCl, HBr, HI, HNO 3 , HClO 4 </li></ul><ul><li>Bases: NaOH, KOH,Ca(OH) 2 , Alkali and Alkaline earth’s </li></ul>
  23. 23. Strong Acids and Strong Bases <ul><li>HA (aq)  H + (aq) + A - (aq) </li></ul><ul><li>BOH (aq)  B + (aq) + OH - (aq) </li></ul><ul><li>Notice the one-way arrow. </li></ul>
  24. 24. What is the pH of a 0.011 M solution of Ca(OH) 2 ?
  25. 25. Weak Acids  partially ionized <ul><li>HA (aq)  H + (aq) + A - (aq) </li></ul><ul><li>Notice the arrow </li></ul><ul><li>This is an equilibrium reaction and all the rules of equilibrium can be applied to this equation </li></ul>
  26. 26. Equilibrium Expression <ul><li>K a = Acid- Dissociation Constant </li></ul><ul><li>The larger the value of K a the stronger the acid. </li></ul>
  27. 27. <ul><li>Calculating K a </li></ul><ul><li>A student prepared a 0.10 M solution of formic acid, HCHO 2 , and measured its pH at 25 o C to be 2.38. </li></ul><ul><ul><li>Calculate K a. </li></ul></ul><ul><ul><li>What percentage of formic acid is ionized. </li></ul></ul>
  28. 28. Niacin Overhead Question page 7
  29. 29. pH calculations of Weak Acids <ul><li>Calculate the pH of a 0.30 M Solution of acetic acid at 25 o C. What percent ionizes? </li></ul>
  30. 30. <ul><li>Calculate the pH of a 0.20 M solution of HCN. Percent ionization? </li></ul>
  31. 31. <ul><li>What is the pH of a 0.10 M Solution of niacin? </li></ul>
  32. 32. <ul><li>Calculate the percentage of HF molecules ionized in </li></ul><ul><ul><li>a) 0.10 M HF solution </li></ul></ul><ul><ul><li>b) 0.010 M HF solution </li></ul></ul><ul><ul><li>According to LeChatlier’s principle what is the result of diluting this solution by a factor of 10. Why? </li></ul></ul>
  33. 33. <ul><li>Calculate the percentage of niacin molecules ionized in </li></ul><ul><ul><li>in a 0.010 M solution. </li></ul></ul><ul><ul><li>in a 0.001 M solution. </li></ul></ul>
  34. 34. Polyprotic Acids <ul><li>An acid with more than one proton that can ionize. </li></ul><ul><li>K a1 , K a2 , K a3 </li></ul><ul><li>H 2 SO 3  H + + HSO 3 - K a = </li></ul><ul><li>HSO 3 -  H + + SO 3 - K a = </li></ul>
  35. 35. <ul><li>Calculate the pH and concentration of oxalate ion, [C 2 O 4 2 - ], in a 0.020 M solution of oxalic acid, H 2 C 2 O 4 . </li></ul><ul><li>Note: Two Parts: </li></ul><ul><ul><ul><ul><ul><li>1. 10 3 will determine pH </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>2. Use concentrations of the ions in K a1 to determine the concentration of the oxalic ion. </li></ul></ul></ul></ul></ul>
  36. 36. <ul><li>Consider polyprotic acids: Is the second ionization always less than the first ionization? Why? </li></ul>
  37. 37. Weak Bases <ul><li>Weak base + H 2 O  Conjugate Acid + OH - </li></ul><ul><li>Most common: </li></ul><ul><li>NH 3 + H 2 O  NH 4 + + OH - </li></ul><ul><li>What is the equilibrium Expression for this equation? </li></ul>
  38. 38. Calculate the [OH - ] in a 0.15M solution of NH 3 ? K b = 1.8 x 10 -5 <ul><li>What is the pOH? </li></ul><ul><li>What is the pH? </li></ul><ul><li>What is the relationship between K b and pH? </li></ul>
  39. 39. Which of the following compounds should have the highest pH as a 0.05 M solution? <ul><li>Pyridine: K b = 1.7 x 10 -9 </li></ul><ul><li>Methylamine :=K b 4.4 x 10 -4 </li></ul><ul><li>Nitrous Acid:=K a= 4.5 x10 -4 </li></ul>
  40. 40. Types of Weak Bases <ul><li>Two Types </li></ul><ul><ul><li>1. Neutral substances that contain an atom with lone pair of electrons that can serve as a proton acceptor. </li></ul></ul><ul><ul><li>NH 3 , NH 2 CH 3 , Caffeine, codeine, amphetamine, etc </li></ul></ul>
  41. 41. Types of Weak Bases <ul><ul><li>2. Anions of weak acids (Conjugate Bases) </li></ul></ul><ul><ul><li>HS - </li></ul></ul><ul><ul><li>CO 3 2- </li></ul></ul>
  42. 42. Example <ul><li>NaClO </li></ul><ul><li>Na + ClO - </li></ul><ul><li>Why is ClO - a base? </li></ul>
  43. 43. <ul><li>A solution is made by adding solid sodium hypochlorite to enough water to make a 2L solution. If the solution has a pH of 10.50, how many moles of NaClO were added to the water? </li></ul>
  44. 44. <ul><li>A solution of NH 3 in water has a pH of 10.50. What is the molarity of the solution? </li></ul>
  45. 45. Relation Between K a & K b <ul><li>What happens when we add an acid to a base? </li></ul><ul><li>HCl + NaOH  H 2 O + NaCl water salt </li></ul><ul><li>What happens when we add an acid reaction to a base reaction? </li></ul>
  46. 46. <ul><li>NH 4 +  NH 3 + H + </li></ul><ul><li>NH 3 + H 2 O  NH 4 + + OH - </li></ul><ul><li>Net ionic Equation </li></ul><ul><li>H 2 O  H + + OH - K = [H + ][OH - ]/[H 2 O] </li></ul>
  47. 47. Remember Reaction 1 + Reaction 2 = Reaction 3 (sum) <ul><li>K 1 x K 2 = K 3 (products) </li></ul><ul><li>K a x K b = [H + ][OH - ] all the other species in the pr oducts cancel out and </li></ul><ul><li>K w = [H + ][OH - ] </li></ul><ul><li>K w = K a x K b </li></ul>
  48. 48. Don’t Get Freaked Out <ul><li>pK a + pK b = pK w = 14.00 </li></ul><ul><li>(-logK a )+(-logK b ) = (-logK w ) </li></ul><ul><li>pH + pOH = 14.00 </li></ul>
  49. 49. <ul><li>Calculate K b for F - . </li></ul><ul><li>Calculate K a for NH 3 . </li></ul><ul><li>Which of the following anions has the largest base-dissociation constant, PO 4 3- , NO 2 - , or N 3 - ? Overhead 21 </li></ul>
  50. 50. 5 points: Acid Base Properties of Salts <ul><li>1. Salts can be acids or bases and are always completely ionized. </li></ul><ul><li>2. Anions of salts derived from weak acids are able to hydrolyze H 2 O. What does this mean? </li></ul><ul><li>A - + H 2 O  HA + OH - </li></ul>
  51. 51. 5 Points: Acid Base Properties of Salts <ul><li>3. Anions of strong acids do not hydrolyze water. IE: NO 3 - Thus, no [H + ] so pH is not influenced. </li></ul>
  52. 52. 5 Points: Acid Base Properties of Salts <ul><li>4. Some salt anions derived from acids have ionizable protons and can be an acid or a base. IE: HSO 3 - = amphoteric </li></ul>
  53. 53. Predict whether the salt Na 2 HPO 4 will form an acidic or basic solution when dissolved in water. Overhead 22
  54. 54. <ul><li>Predict whether the dipotassium salt of citric acid, K 2 HC 6 H 5 O 7 , will form an acidic or basic solution in water. </li></ul>
  55. 55. What can you do? <ul><li>Indicate whether each of the following substances will form an acidic, basic, or neutral solution. </li></ul><ul><li>A. KC 2 H 3 O 2 </li></ul><ul><li>B. NaHCO 3 </li></ul><ul><li>C. CH 3 NH 3 Br </li></ul><ul><li>D. KNO 2 </li></ul><ul><li>E. NH 4 CN </li></ul>
  56. 56. 5 Points: Acid Base Properties of Salts <ul><li>5. All cations save alkali and heavy alkaline earths(Ca 2+ , Sr 2+ , Ba 2+ , Ra 2+ ) act as weak acids in water solutions and they also hydrolyze water. </li></ul>
  57. 57. 5 Points of Acid Base Properties of Salts <ul><li>Ionize/ no hydrolyze </li></ul><ul><li>Li + </li></ul><ul><li>Na + With this in mind, </li></ul><ul><li>K + Ca + the presence of </li></ul><ul><li>Rb + Sr + any of these ions </li></ul><ul><li>Cs + Ba + in solution does </li></ul><ul><li>Fr + Ra + not influence pH. </li></ul>
  58. 58. Consider Aluminum <ul><li>AlCl 3 </li></ul>
  59. 59. pH of a solution of a salt <ul><li>We can predict qualitatively the pH by considering the cations and anions from which the salt was composed. </li></ul>
  60. 60. This can only be done by considering a “Normal Salt”.One without ionizable proton. <ul><li>ie: Not normal NaH 2 PO 4 NaHCO 3 </li></ul>
  61. 61. 4 Rules for predicting pH of a salt. <ul><li>1. Salts derived from a strong base and strong acid have a cation and anion that do not hydrolyze. pH= 7 </li></ul>
  62. 62. <ul><li>2. Salts derived from a strong base and a weak acid have an ion that acts as a relatively strong conjugate base. pH>7 </li></ul>
  63. 63. <ul><li>3. Salts derived from a weak base and a strong acid have a cation that acts as a relatively strong conjugate acid. pH<7 </li></ul>
  64. 64. <ul><li>4. Salt derived from a weak base and a weak acid where both the cation and anion hydrolyze. pH- depends on the extent to which ion hydrolyzes. </li></ul>
  65. 65. Use all 9 rules to solve for the following problems .(1-5)explains why (6-9) work . <ul><li>1. Salts ionize </li></ul><ul><li>2. Anions of weak acids hydrolyze water creating an OH - (base) </li></ul><ul><li>3. Anions of strong acids do not hydrolyze.(pH- not influenced) </li></ul><ul><li>4. Amphoteric anions can act as an acid or a base. </li></ul><ul><li>5. Cations (save heavy alkaline earths/alkali) hydrolyze and act as weak acids. </li></ul>
  66. 66. 9 Rules <ul><li>6. Salts derived from a strong acid and strong base do not hydrolyze. pH=7 </li></ul><ul><li>7. Salts derived from a strong base and weak acid= anion that acts a relatively strong conjugate base. pH>7 </li></ul><ul><li>8. Salts derived from a strong acid and weak base= cation that acts as a relatively strong conjugate acid. pH<7 </li></ul><ul><li>9. Salts derived from a weak acid and weak base= ? Depends on K a and K b. </li></ul>
  67. 67. List the following solutions in order of increasing pH <ul><li>0.1 M Co(ClO 4 ) </li></ul><ul><li>0.1 M RbCN </li></ul><ul><li>0.1 M Sr(NO 3 ) 2 </li></ul><ul><li>0.1 M KC 2 H 3 O 2 </li></ul>
  68. 68. Of the following pairs of salts, which one form the more acidic 0.010 M solution <ul><li>1. NaNO 3 or Fe(NO 3 ) 3 </li></ul><ul><li>2. KBr or KBrO </li></ul><ul><li>3. CH 3 NH 3 Cl or BaCl 2 </li></ul><ul><li>4. NH 4 NO 2 or NH 4 NO 3 </li></ul>
  69. 69. Stomach
  70. 70. Stomach
  71. 71. Which solution will be acidic? <ul><li>1. LiBr </li></ul><ul><li>2. NaBr </li></ul><ul><li>3. NH 4 NO 2 </li></ul><ul><li>4. Fe(NO 3 ) 3 </li></ul><ul><li>5. NaCN </li></ul>
  72. 72. Acid Base behavior and Chemical Structure <ul><li>What is polarity? </li></ul><ul><li>What is electronegativity? </li></ul><ul><li>What is bond Energy? </li></ul>
  73. 73. Hydrogen atoms can act as acids, bases or neither. <ul><li>HCl = Acid </li></ul><ul><li>NaH = Base </li></ul><ul><li>H-C in CH 4 = Neutral </li></ul>
  74. 74. The Strength of an acid depends on three factors. <ul><li>1. Polarity of H-X bond. </li></ul><ul><li>2. Strength of H-X bond. </li></ul><ul><li>3. Stability of Conjugate Base. make a conclusion about stable conjugate base at the end of this section. </li></ul>
  75. 75. Overhead # 30 <ul><li>1. Metal hydrides are bases or neutral. </li></ul><ul><li>2. Non-metal hydrides are neutral or acidic. (save NH 3 ) </li></ul>
  76. 76. Overhead # 30 <ul><li>3. Vertical row of non-metals has a tendency toward increasing acidity with increasing atomic number. </li></ul>
  77. 77. Oxyacids- When O-H bonds and additional O are bound to a central atom. <ul><li>O-H can be an acid or a base. </li></ul>
  78. 78. General Rule 1 <ul><li>1 . As the ability of Y to attract electrons increases, the acidity of the substance will also increase. 2 reasons </li></ul><ul><ul><li>A. Y’s EN  : O - H is more polar and thus favors the loss of H + . </li></ul></ul><ul><ul><li>B. Because the conjugate base is usually an anion, its stability generally increases as the electronegativity of Y increases. The reverse reaction is not going to happen that easily due to Y’s EN. Example </li></ul></ul>
  79. 79. General Rule #2 <ul><li>For oxyacids that have the same central atom Y, acid strength increases as the number of oxygen atoms attached to Y increases. Note: This is true of the addition of any relative electronegative anion. </li></ul>
  80. 80. Arrange the compound according to increasing acid strength. <ul><li>1. AsH 3 , HI, NaH, H 2 O </li></ul><ul><li>2. H 2 SeO 3 , H 2 SeO 4 , , H 2 O </li></ul>
  81. 81. <ul><li>In each of the following pairs, choose the compound that leads to the more acidic (or more less) solution. </li></ul><ul><li>1. HBr or HF </li></ul><ul><li>2. PH 3 or H 2 S </li></ul><ul><li>3. HNO 2 or HNO 3 </li></ul><ul><li>4. H 2 SO 3 or H 4 SiO 4 </li></ul>
  82. 82. Carboxyl Acids <ul><li>COOH- Group </li></ul><ul><li>Formic Acid- ant and wasp acid </li></ul><ul><li>Benzoic Acid </li></ul><ul><li>Acetic Acid </li></ul>
  83. 83. <ul><li>What happens to the acidity if CH 3 COOH is changed to CF 3 COOH? </li></ul>
  84. 84. Lewis Acids and Bases <ul><li>Lewis Acids: Electron pair acceptor. </li></ul><ul><li>Lewis Base: Electron Pair donor. </li></ul><ul><li>All species that were classified as a Bronsted-Lowery/Arrhenius acid or base can also be classified Lewis Acid or base. </li></ul>
  85. 85. However, Lewis Acids and bases have an advantage. <ul><li>More species can be classified as Lewis Acids or a Bases because we are not referring to only H + ions(Protons). </li></ul><ul><li>To see the big picture you need the Lewis structure for viewing. </li></ul><ul><li>For Example: H + + NH 3  NH 4 + </li></ul>
  86. 86. Other Examples <ul><li>CO 2 + H 2 O  Carbonic Acid= dead fish. </li></ul><ul><li>NH 3 + BF 3 </li></ul><ul><li>Fe 3+ in Water </li></ul>

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