Answer Key_Exam 3 - Version 044 Exam 3 rowland (53210) 1...

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Unformatted text preview: Version 044 Exam 3 rowland (53210) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Choose the pair of concentrations that cannot be in a given aqueous solution at 25 C. 1. [H 3 O + ] = 10 14 M : [OH ] = 1 M 2. Any of these could exist. correct 3. [H 3 O + ] = 10 3 M : [OH ] = 10 11 M 4. [H 3 O + ] = 10 M : [OH ] = 10 15 M 5. [H 3 O + ] = 10 7 M : [OH ] = 10 7 M Explanation: All of these concentrations are possible. Re- call that pH can exist beyond the 1-14 range, but at 25 C, pH + pOH = 14 always applies. 002 10.0 points According to the Arrhenius Theory, an acid produces ? and a base produces ? . 1. hydroxide ions (OH ); hydrogen ions (H + ) 2. protons; electrons 3. hydrogen ions (H + ); hydroxide ions (OH ) correct 4. electrons; protons Explanation: The Arrhenius theory of acids and bases defines acids as substances which ionize in water to produce hydrogen ions and bases as substances which in water give off hydroxide ions. 003 10.0 points What is [OH ] in a 0.0050 M HCl solution? 1. 5 . 10 3 M 2. 6 . 6 10 5 M 3. 1 . 0 M 4. 1 . 10 7 M 5. 2 . 10 12 M correct Explanation: [OH ] = 0 . 0050 M Since HCl is a strong acid, it completely dissociates and H + is 0 . 0050 M. HCl H + + Cl K w = [H + ][OH ] = 1 10 14 [OH ] = K w [H + ] = 1 10 14 . 0050 = 2 10 12 M 004 10.0 points Carbonic acid (H 2 CO 3 ) is a diprotic acid with K a1 = 4 . 2 10 7 and K a2 = 4 . 8 10 11 . The ion product for water is K w = 1 . 10 14 . What is the [H 3 O + ] concentration in a saturated carbonic acid solution that is 0.037 molar? 1. 7 . 4 10 2 M 2. 4 . 2 10 7 M 3. 6 . 5 10 4 M 4. 1 . 2 10 4 M correct 5. 3 . 7 10 20 M Explanation: 005 10.0 points Calculate the concentration of H 2 SO 3 present in 0 . 123 M Na 2 SO 3 (aq). 1. None of these 2. 4 . 16667 10 8 M Version 044 Exam 3 rowland (53210) 2 3. 8 . 33333 10 8 M 4. 3 . 33333 10 13 M 5. 1 . 33333 10 12 M 6. 6 . 66667 10 13 M correct Explanation: K a1 = 0 . 015 K a2 = 1 . 2 10 7 K w = 1 10 14 The equilibrium reactions of interest are now the base forms of the carbonic acid equi- libria, so K b values should be calculated for the following changes: SO 2 3 (aq) + H 2 O( ) OH (aq) + HSO 3 (aq) K b1 = K w K a2 = 1 10 14 1 . 2 10 7 = 8 . 33333 10 8 . HSO 3 (aq) + H 2 O( ) OH (aq) + H 2 SO 3 (aq) K b2 = K w K a1 = 1 10 14 . 015 = 6 . 66667 10 13 ....
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This note was uploaded on 01/30/2010 for the course GOV 312L taught by Professor Madrid during the Fall '07 term at University of Texas at Austin.

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Answer Key_Exam 3 - Version 044 Exam 3 rowland (53210) 1...

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