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Unformatted text preview: Version 034 – Exam 3 – Sutcliffe – (53770) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. THIS EXAM IS FOR Dr. SUTCLIFFE’s TTH SECTION ONLY. CHECK YOU BUB- BLED YOUR NAME, EID AND VERSION NUMBER CORRECTLY. 001 10.0 points In the reaction Cu 2+ + Fe → Cu + Fe 2+ 1. iron is reduced. 2. copper(II) is the reducing agent. 3. iron is oxidized. correct 4. copper is oxidized. Explanation: The oxidation number of an element in a monatomic ion is simply the charge on the ion, so Cu in Cu 2+ and Fe in Fe 2+ both have oxidation numbers of +2. The oxida- tion number of a free, uncombined element is zero. Oxidation is the loss of electrons, which corresponds to an algebraic increase in oxi- dation number. The oxidation number of Fe changes from 0 to +2, so Fe is oxidized. 002 10.0 points All of the following are strong acids except 1. hydrochloric acid. 2. nitric acid. 3. sulfuric acid. 4. acetic acid. correct Explanation: All of the acids, except for the acetic acid, hydrolyze completely in water to give H 3 O + . Acetic acid only partially hydrolyzes, produc- ing H 3 O + . 003 10.0 points A(n) 0.65 mole quantity of O 2 originally at 85 ◦ C is cooled such that it now occupies 4.0 L at 20. ◦ C. What is the final pressure exerted by the gas? 1. 3.9 atm correct 2. 0.92 atm 3. 1.1 atm 4. Not enough information is given. 5. 6.2 atm 6. 0.27 atm Explanation: T = 20 ◦ C + 273 = 293 K V = 4 . 0 L n = 0 . 65 mol Using the Ideal Gas Law, P V = n RT P = n RT V = (0 . 65 mol) (0 . 082058 L · atm mol · K ) (293 K) 4 . 0 L = 3 . 9 atm 004 10.0 points How many moles of hydrogen atoms does each mole of (NH 4 ) 2 CO 3 contain? 1. 1 mol 2. 8 mol correct 3. 12 mol 4. 4 mol 5. 2 mol Explanation: There are 8 mol H atoms in each molecule of (NH 4 ) 2 CO 3 . This same ratio holds for the number of moles of H in one mole of (NH 4 ) 2 CO 3 . This can be seen by starting with the atom to molecule ratio and convert- ing both atoms and molecules to moles using Version 034 – Exam 3 – Sutcliffe – (53770) 2 Avogadro’s number: ? mol H mol (NH 4 ) 2 CO 3 = 8 mol H atoms 1 molec (NH 4 ) 2 CO 3 × 1 mol H 6 . 022 × 10 23 atoms H × 6 . 022 × 10 23 molec (NH 4 ) 2 CO 3 1 mol (NH 4 ) 2 CO 3 = 8 mol H 1 mol (NH 4 ) 2 CO 3 The Avogadro’s number conversions cancel out leaving us with the same mol to mol ratio as the atom to molecule ratio. Therefore there are 8 mol H in one mole of (NH 4 ) 2 CO 3 . 005 10.0 points Nitroglycerin has a formula C 3 H 5 (NO 3 ) 3 . What is the molar mass of nitroglycerin? 1. 398 g 2. 309 g 3. 227 g correct 4. 65 g Explanation: 006 10.0 points How many moles of oxygen atoms (not molecules) are present in 1 . 61 × 10 25 molecules of dinitrogen pentoxide (N 2 O 5 )?...
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This note was uploaded on 03/11/2009 for the course CHEM 301 taught by Professor Wandelt during the Spring '08 term at University of Texas at Austin.

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Exam 3-solutions - Version 034 – Exam 3 – Sutcliffe –(53770 1 This print-out should have 25 questions Multiple-choice questions may continue

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