The catalytic efficiency of an enzyme is called its

Chapter 18, Problem 18.168

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The catalytic efficiency of an enzyme is called its activity and refers to the rate at which it catalyzes the reaction. Most enzymes have optimum activity over a relatively narrow pH range, which is related to the pH of the local cellular fluid. The pH pro- files of three digestive enzymes are shown. 829 PH3BCl3(s) is introduced into a 3.0-L container at a certain temperature, 8.4?103 mol of PH3 is present at equilibrium: (a) Find Kc for the reaction at this temperature. (b) Draw a Lewis structure for the reactant. 18.172 A 1.000 m solution of chloroacetic acid (ClCH2COOH) freezes at 1.93?C. Find the Ka of chloroacetic acid. (Assume the molarities equal the molalities.) 18.173 Sodium stearate (C17H35COONa) is a major component of bar soap. The Ka of the stearic acid is 1.3?105 . What is the pH of 10.0 mL of a solution containing 0.42 g of sodium stearate? 18.174 Calcium propionate [Ca(CH3CH2COO)2; calcium propanoate] is a mold inhibitor used in food, tobacco, and pharmaceuticals. (a) Use balanced equations to show whether aqueous calcium propionate is acidic, basic, or neutral. (b) Use Appendix C to find the resulting pH when 8.75 g of Ca(CH3CH2COO)2 dissolves in enough water to give 0.500 L of solution. 18.175 A site in Pennsylvania receives a total annual deposition of 2.688 g/m2 of sulfate from fertilizer and acid rain. The ratio by mass of ammonium sulfate/ammonium bisulfate/sulfuric acid is 3.0/5.5/1.0. (a) How much acid, expressed as kg of sulfuric acid, is deposited over an area of 10. km2 ? (b) How many pounds of CaCO3 are needed to neutralize this acid? (c) If 10. km2 is the area of an unpolluted lake 3 m deep and there is no loss of acid, what pH would be attained in the year? (Assume constant volume.) 18.176 (a) If Kw ? 1.139?1015 at 0?C and 5.474?1014 at 50?C, find [H3O] and pH of water at 0?C and 50?C. (b) The autoionization constant for heavy water (deuterium oxide, D2O) is 3.64?1016 at 0?C and 7.89?1015 at 50?C. Find [D3O] and pD of heavy water at 0?C and 50?C. (c) Suggest a reason for these differences. 18.177 HX ( ? 150. g/mol) and HY ( ? 50.0 g/mol) are weak acids. A solution of 12.0 g/L of HX has the same pH as one containing 6.00 g/L of HY. Which is the stronger acid? Why? 18.178 The beakers below depict the aqueous dissociations of weak acids HA (blue and green) and HB (blue and yellow); solvent molecules are omitted for clarity. If the HA solution is 0.50 L, and the HB solution is 0.25 L, and each particle represents 0.010 mol, find the Ka of each acid. Which acid, if either, is stronger? PH3BCl3(s) BA PH3(g) BCl3(g). Enzyme activity pH Pepsin Salivary amylase Trypsin 2 4 6 8 10 Salivary amylase begins digestion of starches in the mouth and has optimum activity at a pH of 6.8; pepsin begins protein digestion in the stomach and has optimum activity at a pH of 2.0; and trypsin, released in pancreatic juices, continues protein digestion in the small intestine and has optimum activity at a pH of 9.5. Calculate [H3O] in the local cellular fluid for each enzyme. 18.169 Acet