Exam4Key - EXAM IV CHEM 103a Fall Semester, 2007 Created by...

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EXAM IV Name: ________ KEY_________________ CHEM 103a Fall Semester, 2007 Created by Dr. J. Pollard 100 points DO NOT REMOVE THIS PAGE SHOW ALL WORK FOR CREDIT /25 /30 /30 /15 /100
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Periodic Table (2 7 7) * Lanthanides 58 Ce 140.1 59 Pr 140.9 60 Nd 144.2 61 Pm (145) 62 Sm 150.4 63 Eu 152.0 64 Gd 157.3 65 Tb 158.9 66 Dy 162.5 67 Ho 164.9 68 Er 167.3 69 Tm 168.9 70 Yb 173.0 71 Lu 175.0
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1) (25) Flask A contains 500 ml of 2.5 M Na 2 CO 3 and flask B contains 300 ml of 2.5 M CaCl 2 . When mixed together, a precipitate forms. Show your work for credit. 2.5 M Na 2 CO 3 2.5 M CaCl 2 A B a) (2) Write the net ionic equation for the formation of the precipitate. 2 Na + (aq) + CO 3 2- (aq) + Ca 2+ (aq) + 2 Cl - (aq) 2 Na + (aq) + 2 Cl - (aq) + CaCO 3 (s) CO 3 2- (aq) + Ca 2+ (aq) CaCO 3 (s) b) (8) Calculate, in grams, the mass of the precipitate formed. - 2 3 3 2 - 2 3 3 2 3 2 3 2 CO mols 1.25 CO Na mol CO mol * CO Na L CO Na mol 5 . 2 * 1 CO Na L 5 . 0 = - 2 2 - 2 2 2 2 Ca mols 0.75 CaCl mol Ca mol * CaCl L CaCl mol 5 . 2 * 1 CaCl L 3 . 0 = = limiting reactant 3 3 - 2 3 - 2 CaCO mol CaCO g 100 * Ca mol CaCO mol * 1 Ca mols 75 . 0 = 75 g CaCO 3 (s) c) (12) What is the concentration of all remaining ions in solution? L 0.3 L 0.5 Na mols 2.5 CO Na mol Na mol 2 * CO Na L CO Na mol 5 . 2 * 1 CO Na L 5 . 0 3 2 3 2 3 2 3 2 + = + + = 3.125 M Na + L 0.3 0.5L Cl mols 1.5 CaCl mol Cl mol 2 * CaCl L CaCl mol 5 . 2 * 1 CaCl L 3 . 0 - 2 - 2 2 2 + = = 1.875 M Cl - CO 3 2- = 1.25 mols originally – 0.75 mols ppt w/Ca 2+ = 0.5 mols CO 3 2- remain in soln L 0.3 L 5 . 0 CO mols 5 . 0 - 2 3 + = 0.625 M CO 3 2- d) (3) If the mixture caused a reduction in the potential energy of the system, would the reaction be exothermic or endothermic?
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Exam4Key - EXAM IV CHEM 103a Fall Semester, 2007 Created by...

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