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ch304 exam2 solution_pdf

# ch304 exam2 solution_pdf - Version 067 Exam02 Walker(53970...

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Version 067 – Exam02 – Walker – (53970) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. There may be cases in which more than one answer seems correct. In all cases, select the BEST answer for the question. 001 8.0 points From the list below, select the groups which are allotropes. 1. carbon, silicon, germanium 2. graphite, diamond, C-60 (fullerene) cor- rect 3. carbon dioxide, oxygen 4. carbon dioxide, carbon monoxide Explanation: Allotropes are different forms of the same element in the same physical state. Graphite, diamond, and C-60 (fullerene) are all different forms of solid carbon. 002 8.0 points What is the energy of a photon of light with a frequency of 6 . 0 × 10 14 s - 1 ? 1. 1 . 2 × 10 - 18 J 2. 5 . 0 × 10 - 7 J 3. 1 . 2 × 10 18 J 4. 1 . 3 × 10 - 27 J 5. 3 . 9 × 10 - 19 J correct Explanation: Energy is equal to Planck’s constant times frequency. Planck’s constant is 6 . 6262 × 10 - 34 J · s, and the frequency is given, so E = h ν = ( 6 . 6262 × 10 - 34 J · s )( 6 . 0 × 10 14 s - 1 ) = 3 . 9 × 10 - 19 J 003 8.0 points Why does stratospheric ozone protect us from harmful radiation that O 2 cannot? 1. Being so high in the atmosphere the ozone can absorb the harmful radiation before it gets to the troposphere where the O 2 concentra- tion is the highest. 2. Ozone absorbs radiation whose energy is suffficient to cause biological damage but not high enough to be absorbed by O 2 . correct 3. Since the mass of ozone is greater than the mass of O 2 , it is a better UV absorber. 4. Ozone is produced and destroyed by a complicated series of reactions that require the absorption of UV radiation. 5. Ozone scatters light more strongly that O 2 , thus redirecting it away from the surface of the Earth. Explanation: Oxygen has one bond, of bond order 2 · · · · O · · · · O and ozone two bonds, each of bond order 1.5 · · · · O ·· O · · · · ·· O · · · · ·· O ·· O · · · · O because it exhibits resonance. The higher the order of a bond, the higher the energy required to break it. UV-C protons have sufficient energy to break a bond in either oxygen or ozone; UV-B photons only have enough energy to break a bond in ozone. Thus only ozone protects us from UV-B radiation.

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