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Unformatted text preview: Version 161 Exam One: Shear Shear (52375) 1 This printout should have 30 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 12.0 points When the reaction P 4 O 10 + KOH K 3 PO 4 + H 2 O is balanced, how much KOH is required to react with 3 moles of P 4 O 10 ? 1. 27 mol 2. 18 mol 3. 36 mol correct 4. 9 mol 5. 3 mol Explanation: n P 4 O 10 = 3.0 mol The balanced chemical equation for this reaction is P 4 O 10 + 12 KOH 4 K 3 PO 4 + 6 H 2 O . From the coefficients we see that 12 mol KOH are required for each mole of P 4 O 10 reacted. We use this ratio to calculate the moles of KOH required to react 3 mol P 4 O 10 : ? mol KOH = 3 mol P 4 O 10 12 mol KOH 1 mol P 4 O 10 = 36 mol KOH 002 10.0 points An electron in a hydrogen atom could un dergo any of the transitions listed below, by emitting light. Which transition would give light of the shortest wavelength? Hint: Think Planck, remember Bohr. You may also want to think about the Rydberg equation, but it is not necessary to do the calculations. 1. n = 4 to n = 1 correct 2. n = 3 to n = 1 3. n = 2 to n = 1 4. n = 4 to n = 2 5. n = 4 to n = 3 Explanation: Photons with shorter wavelengths have more energy than those with longer wave lengths. n = 1 is the lowest energy level, the energy increases as n increases. A transition from n = 4 to n = 1 will release more energy than any other option given. 003 10.0 points The photoelectric effect provided evidence for the (wave, particle)like behavior of light. The phenomenon of diffraction provided evidence for the (wave, particle)like behavior of light. 1. wave, particle 2. wave, wave 3. particle, wave correct 4. particle, particle Explanation: The photoelectric effect demonstrates par ticle behavior and diffraction wave behavior. 004 12.0 points Radio station KLBJ broadcasts at a frequency of 93 . 7 10 6 s 1 . Determine the length of the waves that corresponds to this frequency. 1. 2 10 8 m 2. 2 nm 3. 93.7 m 4. 3.20 nm 5. 3.20 m correct Explanation: Version 161 Exam One: Shear Shear (52375) 2 005 12.0 points The molecular formula for ethyl chloride (C 2 H 5 Cl). What is the molecular weight of ethyl chloride? 1. 48.5 grams/mol 2. 69.5 grams/mol 3. 64.5 grams/mol correct 4. 8 grams/mol 5. 34.0 grams/mol Explanation: The formula weight of a compound is based on the atomic weights of the elements in the compound. Each mole of C 2 H 5 Cl contains 2 mol of C, 5 mol of H, and 1 mol of Cl. We know the atomic masses of each of these elements from the periodic table. Using these atomic masses we calculate the grams of each of these elements in one mole of C 2 H 5 Cl: m C = 2 mol C 12 . 01 g C 1 mol C = 24 . 02 g C m H = 5 mol H 1 . 01 g H 1 mol H = 5 . 05 g H m Cl = 1 mol Cl 35 . 45 g Cl 1 mol Cl = 35 . 45 g Cl To get the mass of one mole of C 2 H 5 Cl we add the masses of the component parts. This is the formula weight: FW C 2 H 5 Cl = 24 .....
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This note was uploaded on 11/08/2010 for the course CHEM 301 taught by Professor Wandelt during the Spring '08 term at University of Texas at Austin.
 Spring '08
 wandelt
 Chemistry, Reaction

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