Chapter 15 Acids and Bases Part II Georgia Gwinnett College Chem 1212K Fall 2013 B Shepler Chapter 15 1 Conjugate Acids and Bases The conjugate of an acid often an anion can act as a base The stronger the acid the weaker is its conjugate base The conjugate of a base often a cation can act as an acid The stronger the base the weaker is its conjugate acid The Ka and Kb of a conjugate acid base pair are related K a K b K w Chapter 15 2 Conjugates Continued Conjugates of Acids The conjugate of a strong acid is neutral The conjugate of a weak acid is a weak base Conjugates of Bases The conjugate or counter ion of a strong base is neutral The conjugate of a weak base is a weak acid Small highly charged cations are weak acids Chapter 15 3 Small Highly Charge Metal Cations Most cations except alkali metals and alkaline earth metals from slightly acidic solutions Al3 aq 6H2O l Al H2O 63 aq Chapter 15 4 Examples Classify the following anions as a weak base or neutral C2H3O2 NO3 SO2 Cl Classify the following cations as a weak acid or neutral Na Fe3 CH3NH3 Chapter 15 5 Classifying Salts as Acidic Basic or Neutral Consider the cation and anion individually Determine whether the anion is basic or neutral Determine whether the cation is acidic or neutral If anion is basic and cation is acidic then compare their Kb and Ka The larger one wins Remember that the relationship KaxKb Kw only works for conjugate pairs However you can use this if you only know the dissociation constant of one half of a conjugate pair Chapter 15 6 Chapter 15 7 Chapter 15 8 Example Classify the following as acidic basic or neutral SrBr2 Ba C2H3O2 2 Cr NO3 2 NH4Cl NH4ClO Chapter 15 9 Example Calculate the pH of 0 30 M RbNO2 Chapter 15 10 Lewis Acids and Bases We have a third definition of acids and bases that is still broader than the Bronsted Lowry Definition Lewis Acids and Bases A Lewis acid Electron pair acceptor A Lewis base Electron pair donor Examples H NH3 BF3 NH3 Chapter 15 11 Example Classify each species as a Lewis Acid or Lewis Base Fe 3 NH3 CN Identify the Lewis acid and Lewis base from the reactants Fe3 aq 6H2O l Fe H2O 63 aq CH3 3N g BF3 g CH3 3NBF3 s Chapter 15 12