HW1 - padilla(tp5647 – Homework 1 – Sutcliffe –(53770...

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Unformatted text preview: padilla (tp5647) – Homework 1 – Sutcliffe – (53770) 1 This print-out should have 25 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. 46. correct 2. Cannot be determined 3. 116. 4. 81. 5. 35. Explanation: For A Z X , A = mass number = # p + + # n and Z = atomic number = # p + . A = 81, so # n = A- # p + = 81- 35 = 46 002 10.0 points How many protons and electrons are present in the Mg 2+ ion? 1. 14 protons, 10 electrons 2. 10 protons, 10 electrons 3. 14 protons, 12 electrons 4. 12 protons, 14 electrons 5. 12 protons, 12 electrons 6. 10 protons, 12 electrons 7. 12 protons, 10 electrons correct 8. 10 protons, 14 electrons 9. 14 protons, 14 electrons 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. 121.75 amu correct 2. 121.54 amu 3. 122.38 amu 4. 121.17 amu 5. 122.15 amu 6. 123.45 amu Explanation: Average Atomic Mass = 0 . 5725(120 . 9038) + 0 . 4275(122 . 8831) = 121 . 75 amu 004 10.0 points The atomic weight of a newly discovered el- ement is 110.352 amu. It has two naturally occuring isotopes. One has a mass of 111.624 amu. The other has an isotopic mass of 109.875 amu. What is the percent abundance of the last isotope (109.875 amu)? 1. 72.7% correct 2. 62.5% 3. 27.3% 4. 54.2% 5. 37.5% 6. 45.8% Explanation: padilla (tp5647) – Homework 1 – Sutcliffe – (53770) 2 Let x = the percent abundance of the last isotope. Then the percent abundance of the first isotope would be 1- x . Remember that x is the decimal form of the percent, and is some fraction of 1. (109 . 875) x + (111 . 624)(1- x ) = 110 . 352 109 . 875 x + 111 . 624- 111 . 624 x = 110 . 352- 1 . 749 x =- 1 . 272 x = 0 . 727 = 72 . 7% 005 10.0 points What is the formula for the simplest sta- ble compound formed between fluorine and nitrogen? 1. NF 3 correct 2. N 3 F 3. N 2 F 3 4. NF 2 Explanation: N has 5 valence e- and wants to share 8 e- ....
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HW1 - padilla(tp5647 – Homework 1 – Sutcliffe –(53770...

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