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acids and bases Presentation Transcript

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