CHEM301 F08 CA3Akey

CHEM301 F08 CA3Akey - CHEM301, Fall 2008 Dr. Ruder 1 Class...

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CHEM301, Fall 2008 Dr. Ruder 1 Class Activity 3A Acids and Bases Part A : Acids/Bases and pKa values Model 1: Acid-Base Definitions Arrhenius Brønsted-Lowry Lewis Acid Gives H 3 O + in water Donates H + Accepts electron pair Base Gives HO - in water Accepts H + Donates electron pair HA + H 2 O H 3 O + A Questions: 1. (a). In the Brønsted-Lowry definition , what is the role of an acid? (b). Which reagent in the reaction shown in Model 1, acts as an acid, HA or H 2 O? 2 . (a). In the Brønsted -Lowry definition , what is the role of a base? (b). Which reagent in the reaction shown in Model 1, acts as a base, HA or H 2 O? 3. (a). In the Lewis definition, what is the role of an acid? (b). Which reagent in the reaction shown in Model 1, acts as a Lewis acid, HA or H 2 O? 4. (a). In the Lewis definition, what is the role of a base? (b). Which reagent in the reaction shown in Model 1, acts as a Lewis base, HA or H 2 O? 5. In the equation shown in Model 1, label the acid, base, conjugate acid and conjugate base. 6. (a). Which definition, Brønsted -Lowry or Lewis, best describes what occurs during the reaction shown below? Explain why one definition is favored. Al Cl Cl Cl Cl Cl + Al Cl Cl Cl Cl Cl (b). Label each reactant as acid and base. Model 2: Acid Dissociation Constant, Ka and pKa
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CHEM301, Fall 2008 Dr. Ruder 2 The equilibrium constant (Keq) is equal to the concentration of the products over the concentration of the reactants. Since the concentration of water is constant in an acid-base reaction, the equation can be rearranged to define the acid dissociation constant, Ka:: H 3 O Ka = A HA H 2 O Keq = and pKa = -log Ka Questions: 7. (a). If Ka is large, would the concentration of products or the concentration of the reactants be larger? If Ka is large, the acid is
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CHEM301 F08 CA3Akey - CHEM301, Fall 2008 Dr. Ruder 1 Class...

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