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CHEM301 F10 CA3A key

CHEM301 F10 CA3A key - CHEM301 Fall 2010 Dr Ruder 1 Class...

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CHEM301, Fall 2010 Dr. Ruder 1 Class Activity 3A Acids and Bases Part A : Acids/Bases and pKa values Model 1: Acid-Base Definitions Brønsted-Lowry Lewis Acid Donates H Accepts electron pair Base Accepts H Donates electron pair HA + H 2 O H 3 O + A acid base conj. Acid conj. base Questions: 1. (a). In the Brønsted-Lowry definition , what are the roles of an acid and a base? An acid donates a proton and a base accepts a proton. (b). Which reagent in Model 1 is the acid ( HA or H 2 O) and which is the base (HA or H 2 O )? 2 . (a). In the Lewis definition , what are the roles of an acid and a base? An acid accepts electrons and a base donates electrons. (b). Which reagent in Model 1 is the acid ( HA or H 2 O) and which is the base (HA or H 2 O )? 3. In the equation shown in Model 1, label the acid, base, conjugate acid and conjugate base. 4. (a). Which definition, Brønsted -Lowry or Lewis , best describes what occurs during the reaction shown below? Explain why one definition is favored. The Lewis definition is favored because there is not proton transfer in this reaction. Cl2 is the base because it donates electron. Al Cl Cl Cl Cl Cl + Al Cl Cl Cl Cl Cl acid base (b). Label each reactant as acid and base. Model 2: Acid Dissociation Constant, Ka and pKa 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: 5. (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 (circle one) strong / weak. (b). If Ka is large, the pkA is (circle one) small / large.
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