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Chemistry Warm-up-solutions

Chemistry Warm-up-solutions - nanni(arn437 Chemistry...

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nanni (arn437) – Chemistry Warm-up – CNS – (87654) 1 This print-out should have 32 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Simplify parenleftbigg u 3 - 2 w parenrightbigg 4 Your answer should be written with all ex- ponents expanded as far as they can go. De- note division using \ , and use the minimum number of parenthesis consistent with order of operations. Correct answer: u 1 2 / (16 w 4 ). Explanation: First we expand the exponent over the things included in the outer parenthesis, and then we simplify as much as we can: parenleftbigg u 3 - 2 w parenrightbigg 4 = ( u 3 ) 4 ( - 2) 4 w 4 = u 1 2 16 w 4 002 10.0points Simplify (2 z 5 w 3 )(5 w 7 )(2 z ) Your answer should be written with all ex- ponents expanded as far as they can go. De- note division using \ , and use the minimum number of parenthesis consistent with order of operations. Correct answer: 20 * ( z 6 ) * ( w ( 10)). Explanation: We simply multiply all the like terms, re- membering that ( a n )( a m ) = a n + m . So, the right answer is 2 · 5 · 2 z 5+1 w 3+7 = 20 z 6 w 10 003(part1of4)10.0points Balance the following chemical equation by finding values for a,b,c, and d. a C 2 H 5 OH(l) + b O 2 (g) c CO 2 (g)+ d H 2 O(g) What is a? Correct answer: 1. Explanation: In a chemical reaction matter is neither created nor destroyed. So, we proceed by counting elements on both sides. C 2 H 5 OH(l) + O 2 (g) CO 2 (g)+ H 2 O(g) Carbon appears only once on each side of the equation, so to balance the C, we put a 2 in front of the CO 2 and a 1 in front of the C 2 H 5 OH(l) Next the hydrogen. Each molecule of C 2 H 5 OH contains 6 hydrogen atoms. To bal- ance the H, we put a 3 in front of the water. Finally, we match the oxygen in the prod- ucts with the number of oxygen atoms needed in the reactants. On the right hand side of the equation we have 7 oxygen atoms. To balance the oxygen we recognize that there is 1 oxygen atom in C 2 H 5 OH(l) so we need to put a 3 in front of the O 2 (g) The balanced reaction is: 1 C 2 H 5 OH(l) + 3 O 2 (g) 2 CO 2 (g)+ 3 H 2 O(g) 004(part2of4)10.0points What is b? Correct answer: 3. Explanation: See the explanation for part 1. 005(part3of4)10.0points What is c? Correct answer: 2. Explanation: See the explanation for part 1. 006(part4of4)10.0points What is d?
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nanni (arn437) – Chemistry Warm-up – CNS – (87654) 2 Correct answer: 3. Explanation: See the explanation for part 1. 007 10.0points Calculate the volume of a sphere with radius of 3.0 μ m. Answer in cm 3 , to 2 significant digits. Note : Volume formulae are provided in ALEKS Your answer must be within ± 5.0% Correct answer: 1 . 1 × 10 - 10 cm 3 . Explanation: The volume of a sphere is given by V = 4 3 πr 3 . Thus, we find that the volume of the sphere is 4 3 π (3 μ m) 3 = 113 . 097 μ m 3 Now converting to cm 3 V ol cm 3 = 113 . 097 μ m 3 · parenleftbigg 1m 10 6 μ m parenrightbigg 3 · parenleftbigg 10 2 cm 1m parenrightbigg 3 = 113 . 097 μ m 3 · parenleftbigg 1m 3 10 18 μ m 3 parenrightbigg · parenleftbigg 10 6 cm 3 1m 3 parenrightbigg = 113 . 097 μ m 3 parenleftbigg 1cm 3 10 12 μ m 3 parenrightbigg = 1 . 13097 × 10 - 10 cm 3
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