zumdahl_chemprin_6e_csm_ch07

zumdahl_chemprin_6e_csm_ch07 - CHAPTER 7 ACIDS AND BASES...

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192 CHAPTER 7 ACIDS AND BASES Nature of Acids and Bases 16. a. H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) or H 2 O(l) H + (aq) + OH (aq) K = K w = [H + ][OH ] b. HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) or HF(aq) H + (aq) + F (aq) K = K a = ] HF [ ] F ][ H [ + c. C 5 H 5 N(aq) + H 2 O(l) C 5 H 5 NH + (aq) + OH (aq) K = K b = ] N H C [ ] OH ][ NH H C [ 5 5 5 5 + 17. An acid is a proton (H + ) donor, and a base is a proton acceptor. A conjugate acid-base pair differs by only a proton (H + ) in the formulas. C o n j u g a t e C o n j u g a t e A c i d B a s e B a s e o f A c i d A c i d o f B a s e a. H 2 CO 3 H 2 O HCO 3 H 3 O + b. C 5 H 5 NH + H 2 O C 5 H 5 N H 3 O + c. C 5 H 5 NH + HCO 3 C 5 H 5 N H 2 CO 3 18. a. HClO 4 (aq) + H 2 O(l) H 3 O + (aq) + ClO 4 (aq). Only the forward reaction is indicated because HClO 4 is a strong acid and is basically 100% dissociated in water. For acids, the dissociation reaction is commonly written without water as a reactant. The common abbreviation for this reaction is HClO 4 (aq) H + (aq) + ClO 4 (aq). This reaction is also called the K a reaction because the equilibrium constant for this reaction is designated as K a . b. Propanoic acid is a weak acid, so it is only partially dissociated in water. The dissociation reaction is CH 3 CH 2 CO 2 H(aq) + H 2 O(l) H 3 O + (aq) + CH 3 CH 2 CO 2 (aq) or CH 3 CH 2 CO 2 H(aq) H + (aq) + CH 3 CH 2 CO 2 (aq). c. NH 4 + is a weak acid. Similar to propanoic acid, the dissociation reaction is: N H 4 + (aq) + H 2 O(l) H 3 O + (aq) + NH 3 (aq) or NH 4 + (aq) H + (aq) + NH 3 (aq)
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CHAPTER 7 ACIDS AND BASES 193 19. The dissociation reaction (the K a reaction) of an acid in water commonly omits water as a reactant. We will follow this practice. All dissociation reactions produce H + and the conjugate base of the acid that is dissociated. a. HC 2 H 3 O 2 (aq) H + (aq) + C 2 H 3 O 2 ( a q ) K a = ] O H HC [ ] O H C ][ H [ 2 3 2 2 3 2 + b. Co(H 2 O) 6 3+ (aq) H + (aq) + Co(H 2 O) 5 (OH) 2+ (aq) K a = ] ) O H ( Co [ ] ) OH ( ) O H ( Co ][ H [ 3 6 2 2 5 2 + + + c. CH 3 NH 3 + (aq) H + (aq) + CH 3 NH 2 (aq) K a = ] NH CH [ ] NH CH ][ H [ 3 3 2 3 + + 20. Strong acids have a K a >> 1 and weak acids have K a < 1. Table 7.2 in the text lists some K a values for weak acids. K a values for strong acids are hard to determine so they are not listed in the text. However, there are only a few common strong acids so if you memorize the strong acids, then all other acids will be weak acids. The strong acids to memorize are HCl, HBr, HI, HNO 3 , HClO 4 , and H 2 SO 4 . a. HClO 4 is a strong acid. b. HOCl is a weak acid (K a = 3.5 × 10 8 ). c. H 2 SO 4 is a strong acid. d. H 2 SO 3 is a weak diprotic acid because the K a1 and K a2 values are less than 1. 21. The beaker on the left represents a strong acid in solution; the acid HA is 100% dissociated into the H + and A ions. The beaker on the right represents a weak acid in solution; only a little bit of the acid HB dissociates into ions, so the acid exists mostly as undissociated HB molecules in water.
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This note was uploaded on 11/30/2010 for the course CHE 141 taught by Professor Kerber during the Fall '07 term at SUNY Stony Brook.

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zumdahl_chemprin_6e_csm_ch07 - CHAPTER 7 ACIDS AND BASES...

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