ch304 hw6 - dh2964 Homework 6 Walker (53970) This print-out...

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dh2964 – Homework 6 – Walker – (53970) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. NOTE CHANGE TO DUE DATE, because exam03 is on a Wednesday. NOTE CHANGE TO DUE DATE. See Quest For latest due date inFormation. 001 1.0 points The atomic masses For elements are 1. relative masses determined by comparison with a standard reFerence. correct 2. the same as the atomic number. 3. unknown. 4. actual masses determined by weighing individual atoms. Explanation: 002 1.0 points Nitroglycerin has a Formula C 7 H 19 (NO 3 ) 2 . What is the molar mass oF nitroglycerin? 1. 309 g 2. 227 g correct 3. 398 g 4. 65 g Explanation: 003 1.0 points What is the weight oF a single molecule oF CO 2 ? 1. 44 g 2. 6 . 0 × 10 23 g 3. 6 . 0 × 10 - 23 g 4. 7 . 31 × 10 23 g 5. 7 . 31 × 10 - 23 g correct Explanation: We don’t have a direct method oF looking up the mass in grams oF a single molecule, but we can determine the mass in grams oF a mole oF molecules. This is the Formula weight oF the compound and is based on the atomic weights oF the elements in the compound. Each mole oF CO 2 contains 1 mol oF C and 2 mol oF O. We know the atomic masses oF each oF these elements From the periodic table. Using these atomic masses we calculate the Formula weight oF CO 2 : ±W CO 2 = 1 mol C · 12 . 0107 g C 1 mol C + 2 mol O · 15 . 9994 g O 1 mol O = 44 . 0095 g CO 2 mol CO 2 Now we know the grams per mole oF CO 2 . We also know there are Avogadro’s number oF molecules per mole. We can use Avogadro’s number to convert From moles to grams: ? g CO 2 molec CO 2 = 44 . 0095 g CO 2 mol CO 2 × 1 mol CO 2 6 . 022 × 10 23 molec CO 2 = 7 . 30812 × 10 - 23 g / molec 004 1.0 points How many atoms are contained in 1 . 5 × 10 - 2 moles oF iron (atomic weight 55.85)? 1. 6 . 022 × 10 23 atoms 2. ( 1 . 5 × 10 - 2 ) (55.85) atoms 3. ( 1 . 5 × 10 - 2 ) ( 6 . 022 × 10 23 ) atoms cor- rect 4. Not determinable From the inFormation given 5. ( 1 . 5 × 10 - 2 ) (55 . 85) ( 6 . 022 × 10 23 ) atoms Explanation: n = 1 . 5 × 10 - 2 mol
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dh2964 – Homework 6 – Walker – (53970) 2 There are Avogadro’s number of iron (Fe) atoms in one mole of Fe atoms. ? Fe atoms = 1 . 5 × 10 - 2 mol Fe × 6 . 02 × 10 23 atoms Fe 1 mol Fe = ( 1 . 5 × 10 - 2 ) ( 6 . 022 × 10 23 ) 005 1.0 points Which of the following contains the smallest number of molecules? 1. 5.0 g H 2 O 2. 5.0 g N 2 3. 5.0 g O 2 4. 5.0 g CO 2 correct Explanation: H 2 O has the smallest atomic weight and CO 2 has the largest atomic weight. The one with the smallest atomic weight would have the most moles per 5.0 grams. It would therefore also have the most molecules per 5.0 grams. The one with the largest atomic weight would have the fewest moles per 5.0 grams; it would therefore also have the fewest molecules per 5.0 grams: n = 5 . 0 g CO 2 × 1 mol CO 2 44 g CO 2 × 6 . 02 × 10 23 molec 1 mol = 6 . 8 × 10 22 molec CO 2 006 1.0 points Which has more molecules: a gram of CO
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ch304 hw6 - dh2964 Homework 6 Walker (53970) This print-out...

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