# HW1 - momin(rrm497 Homework 1 Sutclie(53120 This print-out...

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momin (rrm497) – Homework 1 – Sutcliffe – (53120) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The number of neutrons in an atom of 81 Br is 1. 116. 2. 46. correct 3. Cannot be determined 4. 81. 5. 35. Explanation: For A Z X , A = mass number = # p + + # n 0 and Z = atomic number = # p + . A = 81, so # n 0 = A - # p + = 81 - 35 = 46 002 10.0 points How many protons and electrons are present in the Mg 2+ ion? 1. 14 protons, 14 electrons 2. 10 protons, 10 electrons 3. 14 protons, 10 electrons 4. 10 protons, 12 electrons 5. 10 protons, 14 electrons 6. 14 protons, 12 electrons 7. 12 protons, 14 electrons 8. 12 protons, 12 electrons 9. 12 protons, 10 electrons correct Explanation: Mg has atomic number 12; it has 12 protons and 12 electrons; Mg 2+ has only 10 electrons. 003 10.0 points A newly discovered element has two isotopes. One has an atomic weight of 120.9038 amu with 57.25% abundance. The other has an atomic weight of 122.8831 amu. What is the atomic weight of the element? 1. 122.15 amu 2. 121.17 amu 3. 121.54 amu 4. 122.38 amu 5. 123.45 amu 6. 121.75 amu correct Explanation: Average Atomic Mass = 0 . 5725(120 . 9038) + 0 . 4275(122 . 8831) = 121 . 75 amu 004 10.0 points Which of these elements does NOT exist as a diatomic molecule in its most stable form? 1. nitrogen 2. oxygen 3. fluorine 4. carbon correct 5. iodine Explanation: H, N, O, F, Cl, Br, and I all exist in nature as diatomic molecules. 005 10.0 points Which compound is an ionic compound? 1. ZnS correct

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momin (rrm497) – Homework 1 – Sutcliffe – (53120) 2 2. SiF 4 3. P 2 O 5 4. NCl 3 5. AsCl 3 Explanation: 006 10.0 points The density of octane is 0.702 g/cm 3 . What is the mass of 65.00 cm 3 of octane?
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