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178Exam3BKeyF06 - STACEY STOFFREGEN FALL 2006 CHEM 178 HOUR...

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STACEY STOFFREGEN CHEM 178 NAME FALL 2006 HOUR EXAM 3 RECIT. INSTR. RECIT. SECT. THIS EXAM CONSISTS OF 13 QUESTIONS ON 6 PAGES SEAT # Teaching Assistants and Recitation Sections FINAL EXAM Name Section Time Monday December 11, 2006 Alex Blom 2,5 9:00, 10:00 Gilman 1002 7:30am-9:30am Sayantan Bose 3,9 9:00, 12:10 Beth Prince 1,4,6 8:00, 10:00, 11:00 Matthew Soyk 7,8 11:00, 12:10 PAGE POINTS SCORE 1 18 pts _________ 2 16 pts _________ 3 22 pts _________ 4 12 pts _________ 5 20 pts _________ 6 12 pts _________ TOTAL 100 pts _________ SHOW ALL OF YOUR WORK ON THESE EXAM PAGES. NUMERICAL ANSWERS SHOULD BE GIVEN IN THE CORRECT NUMBER OF SIGNIFICANT FIGURES AND UNITS. PUT YOUR ANSWERS IN THE ANSWER SPACES. THE LAST PAGE CONTAINS A PERIODIC TABLE. THIS SHOULD BE REMOVED AND USED FOR REFERENCE AND SCRATCH PAPER. THIS IS A CLOSED-NOTE, CLOSED-BOOK EXAM. THE ANSWER KEY TO THIS EXAM WILL BE POSTED ON BULLETIN BOARD #6 IN THE HALLWAY EAST OF ROOM 1002 GILMAN AND ON THE COURSE WEBSITE
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1 1a. (8pts) The dissolution of limestone, CaCO 3 , by rainwater (pH 5-6) is the primary cause of sinkholes and the decomposition of buildings and monuments. The solubility of CaCO 3 is 6.7 × 10 -3 g/L. Calculate the solubility-product constant (K sp ) for CaCO 3 given the equilibrium expression below. CaCO 3 (s) Ca 2+ (aq) + CO 3 2- (aq) 9 5 5 sp 2 3 5 3 2 3 3 3 3 3 2 5 3 2 3 3 3 3 2 3 2 sp 10 4.5 ] 10 7 6 ][ 10 7 6 [ K L molCO 10 7 6 molCaCO 1 molCO 1 gCaCO 087 100 molCaCO 1 L gCaCO 10 7 6 L molCa 10 7 6 molCaCO 1 molCa 1 gCaCO 087 100 molCaCO 1 L gCaCO 10 6.7 ] ][CO [Ca K + + + × = × × = × = × × = × = . . . . . . . 1b. (4pts) Does the solubility of limestone increase, decrease, or remain the same when exposed to acid rain, pH 4.0? Provide justification for your answer. The solubility of CaCO 3 (s) will increase when exposed to acid rain according to Le Châtelier’s principle. Exposure to an increased concentration of H + ions results in the consumption of CO 3 2- to form HCO 3 - , driving the reaction of the dissolution of limestone to the right.
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