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Chapter 9

Chapter 9. Acids and Bases. Autoionization of water. Equation Hydronium ion No free H + , . Autoionization. Dynamic equilibrium. Problem. Write the equilibrium expression for the autoionization of water. In pure water at 25 o C, . Therefore…. K w =

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Chapter 9

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  1. Chapter 9 Acids and Bases

  2. Autoionization of water • Equation • Hydronium ion • No free H+,

  3. Autoionization • Dynamic equilibrium

  4. Problem • Write the equilibrium expression for the autoionization of water. • In pure water at 25oC,

  5. Therefore… • Kw = • How much ion is present, relatively speaking? A lot or a little? • If [H+] increases… what must happen to [OH-]?

  6. Produce H+ Neutralize bases to produce salt water Produce OH- Neutralize acids to produce salt water What are Acids/Bases? Acids Bases

  7. Indicators • Litmus, blue and red • Universal • Phenolphthalein • Red cabbage juice • Phenol red

  8. No equilibrium HCl HI HClO4 Strong Acids

  9. No equilibrium Ba(OH)2 Strong Bases

  10. Practice I • What is the concentration of hydronium ion in a 0.0400 M solution of HNO3?

  11. Practice II • What is the [OH-] in a solution of KOH that ha a concentration of 0.320 M?

  12. Practice III • What is the [H+] in a 0.400 M solution of H2SO4?

  13. Practice IV • What is the [OH-] in a solution of HCl that has a [H+]= 0.00300 M?

  14. Practice V • What is the [H+] in a 0.0500 M Ba(OH)2?

  15. pH • Logarithmic scale • pH

  16. pH • So… if [H+] = • pH = • Pure water

  17. pH • To find [H+] given pH, use • [H+] =

  18. pH scale 1 7 14 Acid Neutral Base

  19. pOH • Calculated the same way, but using [OH-] • pH + pOH = • From Kw =

  20. Weak Acids and Bases • If the acid/base is not one of the strong, it is considered weak • Majority of acids and bases • React with water,

  21. Practice I • Write the equilibrium expression for formic acid reacting with water • Keq =

  22. Practice II • Repeat the above for NH3 reacting with water • Keq = • Also called

  23. Conjugate Acids and Bases • Write the reaction between nitrous acid, HNO2 and water • Write the reaction between nitrite ion and water

  24. Ka and Kb • Multiply • Cancel items that cancel • What do you get?

  25. Practice • What is Ka for carbonate ion if Kb = 2.19 x 10-4

  26. pKa and pKb • Determining Ka from pKa

  27. Polyprotic acids • Write the dissociations for H3PO4, a weak acid. There are three steps • Ka1 = 5.93 e-3 • Ka2 = 6.32 e-8 • Ka3 = 4.84 e-13

  28. Salts and Hydrolysis • Ions of a strong acids or bases • Ions of weak acids and bases

  29. Practice • Predict whether each of the following will make an acidic, basic, or neutral solution. • Mg(NO)3 • K2CO3 • NH4NO3

  30. Buffers • Resist changes in pH • Why do companies make buffered aspirin?

  31. Buffer system • Conjugate acid/base pair • Concentrations of each must be about equal

  32. Sponge factor • One ion acts as a sponge for • One ion acts as a sponge for • Greater concentration of acid and base, greater the ability to resist pH changes

  33. Henderson-Hasselbalch [Base] • pH = pKa + log • Tells you what changes in pH will happen with addition of acid or base [Acid]

  34. Practice • Calculate the pH of a solution that is 0.00600 M acetic acid and 0.0080 M sodium acetate. • What is the pH if the concentration of acetic acid is changed to 0.0090 M?

  35. Practice • Determine the buffer system ions to use to have a system pH of 6.1 +/- 0.3

  36. Carbon Dioxide • CO2(aq) + H2O(l) H2CO3(aq) • H2CO3(aq) + H2O(l) H3O+(aq) + HCO3- • pKa • Used in blood to maintain pH at 7.45 • How?

  37. Blood buffer system • Use Henderson-Hasselbalch • pH = pKa + log [HCO3-(aq)] [CO2(aq) +H2CO3(aq)]

  38. Blood buffer system • pKa = • pH-pKa = • So… the rest of the equation must equal 1 • Log 10 = • Therefore the ratio of HCO3-/(CO2+H2CO3) =

  39. Blood buffer system • CO2 is constantly being replaced by metabolic processes and is present in the blood

  40. Blood buffer system • CO2 is constantly lost • If CO2 is removed too fast… problems arise

  41. Smokers • Inhale CO2 • Look at Henderson-Hasselbalch

  42. Respiratory Acidosis • When CO2 not removed or is added from the environment • pH falls • Death

  43. Equations • CO2(aq) + H2O(l) H2CO3(aq) • H2CO3(aq) + H2O(l) H3O+(aq) + HCO3- • LeChatlier’s principal

  44. Respiratory Alkalosis • CO2 removed too fast • Hyperventilation

  45. Metabolic Acidosis • Body attempts to compensate by adding CO2 • Help buffer system by adding HCO3-

  46. Metabolic Alkalosis • Eating too many Rolaids • Add NH4Cl

  47. Titration • Lab experiment • React an acid and base to form water • Measure the endpoint with indicator • Use MaVa = MbVb

  48. Practice • What volume of 0.200 M NaOH is needed to completely neutralize 40.00 mL of 0.0855 M HCl?

  49. Practice II • What volume of 0.250 M KOH is needed to neutralize 50.0 mL of 0.250 M H2SO4?

  50. Practice III • What is the concentration of HCl if 35.00 mL of the acid are neutralized by 61.50 mL of 0.500 M NaOH?

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