Chem 162-2011 Chapter 15A-Some Acid and base equilibria practice problems

Chem 162-2011 Chapter 15A-Some Acid and base equilibria practice problems

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Unformatted text preview: ACID AND BASE CONCEPTS CHEM 162-2007 EXAM II + ANSWERS CHAPTER 15A ACID & BASE EQUILIBRIA ACID AND BASE CONCEPTS 22. Solution A contains 50.0 mL of 0.10 M HCl Solution B contains 50.0 mL of 0.10 M CH 3 COOH Which statements are correct? X. Solution A has a lower pH than solution B Y. Solution A conducts electricity better than solution B Z. Solution A and solution B both require 50.0 mL of 0.10 M NaOH to reach the equivalence point. (a) Y and Z only (b) X and Y only (c) Z only (d) X and Z only (e) X, Y and Z X. Correct. The stronger acid is completely dissociated, providing a high [H 3 O + ]. The weaker acid provides much lower [H 3 O + ]. Y. Correct. Since HCl is a strong electrolyte, it conducts a strong electric current. Since CH 3 COOH is a weak electrolyte, it conducts a weak electric current. Z. Correct. A strong base reacts completely with any acid, whether it is a strong or a weak acid. CHEM 162-2007 EXAM II + ANSWERS CHAPTER 15A ACID & BASE EQUILIBRIA ACID AND BASE CONCEPTS 23. Consider the equation: Al(OH) 3 (s) + OH- (aq) Al(OH) 4- In this reaction, Al(OH) 3 is acting as a: (a) Bronsted acid (b) Bronsted base (c) Lewis acid (d) Lewis base (e) Arrhenius base (a) False. A Bronsted acid is one which shares protons. The Al(OH) 3 has no protons to share. (b) False. A Bronsted base is one which shares protons. The Al(OH) 3 is not sharing electrons. (c) True. A Lewis acid is one which receives electrons. This one is receiving electrons from the OH- . 1 (d) False. A Lewis base is one which shares its electrons. The Al(OH) 3 is not sharing electrons. (e) False. An Arrhenius base is one which donates a OH- . The Al(OH) 3 is not donating a OH- . CHEM 162-2007 EXAM II + ANSWERS CHAPTER 15A ACID & BASE EQUILIBRIA ACID AND BASE CONCEPTS 25. Phosphoric acid is a polyprotic acid with K a values: K a1 = 7.5 x 10-3 K a2 = 6.3 x 10-8 K a3 = 4.8 x 10-13 What is the value of the equilibrium constant for the reaction: HPO 4 2- + H 2 O H 3 O + + PO 4 3- (a) 6.3 x 10-8 (b) 4.8 x 10-13 (c) 1.6 x 10 7 (d) 1.3 x 10-12 (e) 2.1 x 10-2 H 3 PO 4 + H 2 O H 3 O + + H 2 PO 4- K a1 = 7.5 x 10-3 H 2 PO 4- + H 2 O H 3 O + + HPO 4 2- K a2 = 6.3 x 10-8 HPO 4 2- + H 2 O H 3 O + + PO 4 3- K a3 = 4.8 x 10-13 The equation given is identical to the third ionization, K a3 . Hence, K = K a3 = 4.8 x 10-13 . 13. Chem 162-2005 Exam II Acids and Bases - Chapter 14 Lewis acids and bases concepts Which of the following ions is the strongest Lewis acid? A . Al 3+ B. Mg 2+ C. CH 3 COO- D. Cl- E. Na + 2 A, B and E are Lewis acids; C and D are Lewis bases. The strongest Lewis acid should be the one that has the strongest affinity for electrons. This should be the one with the strongest positive charge, hence, Al 3+ ....
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Chem 162-2011 Chapter 15A-Some Acid and base equilibria practice problems

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