Homework 2-solutions

Homework 2-solutions - fernandez (jf23742) Homework 2...

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1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices before answering. This assignment covers electromagnetic ra- diation and atomic structure. The due date is September 17, 2008, at 11:00 pm. 001 10.0 points How many moles of electrons would there be in one mole of He 2+ ? 1. 2 mol 2. 1 mol 3. none correct 4. 4 mol 5. 0.5 mol Explanation: 002 10.0 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. 10.600 2. 11.000 3. 10.000 4. 11.200 5. 10.500 6. 9.0000 7. 11.500 8. 9.5000 9. 12.000 correct 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 10.0 points How many protons and electrons are present in the Mg 2+ ion? 1. 14 protons, 10 electrons 2. 12 protons, 10 electrons correct 3. 12 protons, 12 electrons 4. 12 protons, 14 electrons 5. 10 protons, 12 electrons 6. 14 protons, 12 electrons 7. 10 protons, 10 electrons 8. 14 protons, 14 electrons 9. 10 protons, 14 electrons Explanation: Mg has atomic number 12; it has 12 protons and 12 electrons; Mg 2+ has only 10 electrons. 004

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This note was uploaded on 07/27/2009 for the course CH 89959 taught by Professor Cowley during the Spring '09 term at University of Texas.

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Homework 2-solutions - fernandez (jf23742) Homework 2...

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