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Chapter 16: Acids and Bases

Petrucci • Harwood • Herring • Madura. GENERAL. Ninth Edition. CHEMISTRY. Principles and Modern Applications. Chapter 16: Acids and Bases. Juana Mendenhall, Ph.D. Assistant Professor Morehouse College. Objectives.

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Chapter 16: Acids and Bases

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  1. Petrucci • Harwood • Herring • Madura GENERAL Ninth Edition CHEMISTRY Principles and Modern Applications Chapter 16: Acids and Bases Juana Mendenhall, Ph.D. Assistant Professor Morehouse College General Chemistry: Chapter 16

  2. Objectives Calculate values of Ka for cations and Kb for anions from ionization constants of their conjugates and Kw of water, and calculate the pH values of salt solutions in which hydrolysis occurs Use the relative strengths of Brønsted-Lowry acids and bases to predict the direction of acid-base reactions. Predict whether certain oxides and hydroxo compounds are acidic, basic, or neutral. Define what an oxoacid is and predict the relative strengths of oxoacids from their molecular structures. General Chemistry: Chapter 16

  3. [NH3] [H+] Ka= [NH4+] 1.010-14 KW [NH3][H+] [OH-] Ka= = 5.610-10 = = 1.810-5 Kb [NH4+] [OH-] 16-7 Ions as Acids and Bases NH4+(aq)NH3(aq)+ H+(aq) base acid NH3(aq)+ H2O(l)NH4+(aq) + OH-(aq) [NH4+][OH-] Kb = base acid [NH3] H+(aq) + OH-(aq) H2O(l) [NH4+][OH-] KaxKb = [NH3][H+] Kw [OH-][H+] x = = [NH4+] [NH3] KaKb = Kw pKa + pKb = pKw = 14.00 General Chemistry: Chapter 16

  4. Calculate the a) base-dissociation constant, Kb, for the fluoride ion, F- Examples Ka = 6.8 x 10-4 b) Calculate the acid-dissociation constant, Ka, for the ammonium ion, NH4+ (Kb = 1.8 x 10-5) General Chemistry: Chapter 16

  5. Hydrolysis • is the reaction of ions with water to generate H+ or -OH. • Water (hydro) causing cleavage (lysis) of a bond. Na+ + H2O → Na+ + H2O No reaction No reaction Cl- + H2O → Cl- + H2O Hydrolysis NH4+ + H2O → NH3 + H3O+ General Chemistry: Chapter 16

  6. 16-8 Molecular Structure and Acid-Base Behavior • Why is HCl a strong acid, but HF is a weak one? • Why is CH3CO2H a stronger acid than CH3CH2OH? • There is a relationship between molecular structure and acid strength. • Bond dissociation energies are measured in the gas phase and not in solution. • Strength depends on properties of the solvent and temperature. General Chemistry: Chapter 16

  7. Strengths of Binary Acids HI HBr HCl HF Bond length 160.9 > 141.4 > 127.4 > 91.7 pm Bond energy 297 < 368 < 431 < 569 kJ/mol Acid strength 109 > 108 > 1.3106 >> 6.610-4 HF + H2O → [F-·····H3O+] F- + H3O+ ion pair H-bonding free ions General Chemistry: Chapter 16

  8. 16-9 Lewis Acids and Bases • Lewis Acid • A species (atom, ion or molecule) that is an electron pair acceptor. • Lewis Base • A species that is an electron pair donor. acid base adduct Since BF3 accepts electrons from NH3 it is a lewis acid General Chemistry: Chapter 16

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