1021JDBMidtermExamII(Chapters 4, 6 and 8.6C,E 9th Edition)Fall2009A(AnswerKey)

1021JDBMidtermExamII(Chapters 4, 6 and 8.6C,E 9th Edition)Fall2009A(AnswerKey)

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Dr. Jim Bloxton Answer Key CHEM 1021 Fall 2009 Lecture Midterm II (Chapters 4 and 6 and 8.6C,E From 9 th Edition) Or (Chapters 5 and 7 and 9.6C,E From 8 th Edition) Please put your name, recitation day and time at the top of this exam. All work and calculations for all problems must be shown. Include proper units for each calculation. 1. How does fluoride ion protect the enamel against tooth decay? Fluoride ions replace hydroxide ions in hydroxyapatite and this results in the formation of the less acid soluble fluoroapatite. 2. Would you expect the polar molecule methanol, CH 3 OH, to mix with water? Explain. The alcohol, methanol, CH 3 OH, is a polar molecule that can form hydrogen bonds with the polar molecule water and will mix with water since there are less than 4 carbons for each OH group in methanol. 3. Write the balanced net ionic equation for the reaction of an aqueous solution of, KHCO 3 (aq) with an aqueous solution of the strong acid, HI (aq) . H + (aq) + HCO 3 - (aq) CO 2(g) + H 2 O (l) 4. Calculate the formula weight of Mg 3 (PO 4 ) 2 . Show all calculations. Mg: 3 x 24.31 = 72.93 P: 2 x 30.97 = 61.94 O: 8 x 16.00 = 128.00 -------------------------------------- Formula weight = 262.87 amu and molar mass of Mg 3 (PO 4 ) 2 is 262.87 g/mol. 5. How many moles are found in 645 mg of Mg 3 (PO 4 ) 2 ? Show all calculations. 645 mg x 1 g -------------------------- = 0.645 g MM of Mg 3 (PO 4 ) 2 is 262.87 g/mol. 1000 mg 0.645 g n = ---------------- = 0.00245 mol Mg 3 (PO 4 ) 2 262.87 g/mol
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6. How many moles of magnesium ions are found in 5.88 x 10 24 formula units of Mg 3 (PO 4 ) 2 ? Show all calculations. 5.88 x 10 24 Mg 3 (PO 4 ) 2 formula units x 3 mol Mg 2+ ions ---------------------------------------------------------------------------------------------------- = 6.02 x 10 23 Mg 3 (PO 4 ) 2 formula units/ 1 mole Mg 3 (PO 4 ) 2 x 1 mol Mg 3 (PO 4 ) 2 Final answer = 29.3 mol Mg 2+ ions 7. What is hemodialysis? Hemodialysis is a method to purify blood when kidneys fail. The blood is circulated out of the body and filtered through a machine and circulated back into the body. 8.
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1021JDBMidtermExamII(Chapters 4, 6 and 8.6C,E 9th Edition)Fall2009A(AnswerKey)

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