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conjugate conjugate base acid acid base a) :NH₂ + : + H b) + + 4.5 According to the Lewis acid-base definition, an acid is an electron pair acceptor and a base is an electron pair donor. a) Lewis acid b) Lewis base c) Lewis acid d) Lewis base e) both 4.6 a) 10⁴ b) 16 c) 10⁻³⁸ d) -6 4.7 The acidity constant, Kₐ, is a measure of the acidic strength of a compound. The pKₐ is by definition -log Kₐ. As the strength of an acid increases, its Kₐ increases and its pKₐ decreases. For example, C₂H₂ in (b) has a larger pKₐ than water. Therefore it is a weaker acid than water. a) stronger b) weaker c) stronger d) weaker 4.8 The weaker the acid, the stronger its conjugate base. If the Kₐ of a compound's conjugate acid is larger than that of water (or the pKₐ of the compound's conjugate acid is smaller than that of water), then the compound is a stronger base than hydroxide ion. a) stronger b) stronger c) weaker d) weaker 4.9 The equilibrium favors the formation of the more stable compounds. In the case of acid-base reactions, the weaker acid and the weaker base are favored. For example, in (a) the acid CH₃NH₂ has a lower Kₐ than the acid CH₃CO₂H. Thus CH₃NH₂ is a weaker acid than CH₃CO₂H. Therefore the equilibrium favors the reactants. a) favors reactants b) favors products 50