# HWK2 - Valenica Daniel Homework 2 Due 11:00 pm Inst...

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Valenica, Daniel – Homework 2 – Due: Sep 19 2007, 11:00 pm – Inst: Brodbelt 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Brodbelt CH301 Due Sept. 19, 2007, 11:00 pm Chapter 12 material, Part I 001 (part 1 of 1) 10 points How many moles of electrons would there be in one mole of He 2+ ? 1. 1 mol 2. 2 mol 3. 4 mol 4. none correct 5. 0.5 mol Explanation: 002 (part 1 of 1) 10 points The atomic weight of a newly discovered el- ement is 10.600 amu. It has two naturally occuring isotopes. One has a mass of 10.000 and a natural abundance of 70.000%. What is the isotopic mass of the other isotope? 1. 10.500 2. 9.0000 3. 10.600 4. 9.5000 5. 11.200 6. 12.000 correct 7. 11.500 8. 11.000 9. 10.000 Explanation: The atomic weight equals the sum of the isotopic masses times their natural abun- dance. We know one isotope’s natural abun- dance is 70%, so the other must make up 30%. Let x equal the unknown mass. (10 . 000)(0 . 70) + ( x )(0 . 30) = 10 . 600 7 . 0000 + 0 . 30 x = 10 . 600 0 . 30 x = 3 . 6000 x = 12 . 000 003 (part 1 of 1) 10 points How many protons and electrons are present in the Mg 2+ ion? 1. 14 protons, 12 electrons 2. 14 protons, 10 electrons 3. 12 protons, 14 electrons 4. 10 protons, 10 electrons 5. 10 protons, 12 electrons 6. 10 protons, 14 electrons 7. 14 protons, 14 electrons 8. 12 protons, 10 electrons correct 9. 12 protons, 12 electrons Explanation: Mg has atomic number 12; it has 12 protons and 12 electrons; Mg 2+ has only 10 electrons. 004 (part 1 of 1) 10 points A 200 nm photon has how many times the energy of a 700 nm photon?

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