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Unformatted text preview: Version 026 Exam 2 Mccord (52445) 1 This printout should have 30 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. McCord CH302 10am This exam is only for McCords MWF 10am CH302 class. 001 10.0 points What is the pH of a 0.020 M solution of hydrosulfuric acid, a diprotic acid? K a1 = 1 . 1 10 7 K a2 = 1 . 10 14 1. 5.22 2. 3.65 3. 7.00 4. 9.67 5. 4.33 correct 6. 4.69 7. 7.84 Explanation: Solve using ONLY the 1st ionization. So this works like any other monoprotic acid where the assumption [H + ] = radicalbig (Conc)( K a1 ) is valid. 002 10.0 points The figure represents a reaction at 298 K. b b b b b G A B C D E rxn progress Which statement is FALSE? 1. The position of equilibrium will change if the temperature is changed. 2. The standard free energy of reaction is negative. 3. K is less than 1. correct 4. Pure reactants are represented by point A. Explanation: K is greater than 1 because G is negative (point E has lower free energy than point A). 003 10.0 points Consider the following reaction: PCl 5 (g) PCl 3 (g) + Cl 2 (g) . At equilibrium, [PCl 5 ] = 2.00 M and [PCl 3 ] = [Cl 2 ] = 1.00 M. If suddenly 1.00 M PCl 5 (g), PCl 3 (g), and Cl 2 (g) are each added, calculate the equilibrium concentration of PCl 3 (g). 1. 1.35 M correct 2. 2.32 M 3. 2.18 M 4. 1.43 M 5. 3.35 M 6. 1.95 M Explanation: K = (1)(1) 2 = 0 . 5 after the addition each concentration in creases by 1 M and then the reaction must shift to the left to reestablish equilibrium. K = (2 x ) 2 (3 + x ) = 0 . 5 which converts to 0 = x 2 4 . 5 x + 2 . 5 Version 026 Exam 2 Mccord (52445) 2 The quadratic formula will yield two an swers for x . x = 0 . 64929 or 3 . 85078 The 3.85078 answer is not physically possible and therefore x = 0 . 64929. [PCl 3 ] = 2 x = 1 . 35078 M 004 10.0 points The conjugate base of H 2 SO 4 is: 1. H 3 O + 2. H 2 SO 3 3. H 3 SO + 4 4. SO 2 4 5. HSO 4 correct 6. OH 7. H 2 O Explanation: Remove one H + ion from a species to find its conjugate base. 005 10.0 points Which of the following would be equal to K a 4 for orthocarbonic acid, H 4 CO 4 ? 1. [HCO 3 4 ] [H + ] [CO 4 4 ] 2. [H + ] 4 [CO 4 4 ] [HCO 3 4 ] 3. [H + ] 4 [CO 4 4 ] [H 4 CO 4 ] 4. [H 4 CO 4 ] [H + ] 4 [CO 4 4 ] 5. [H + ] [CO 4 4 ] [HCO 3 4 ] correct Explanation: K a 4 for orthocarbonic acid, H 4 CO 4 , describes the 4 th deprotonation event. HCO 3 4 H + + CO 4 4 006 10.0 points A solution of HClO is mixed and found to have a pH of 3 . 99. Find what the initial concentration of HClO was for this solution. K a = 3 . 00 10 8 for HClO....
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 Spring '07
 Holcombe
 Equilibrium

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