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# HW1 - Lin(cgl286 Homework 1 Lyon(52370 1 This print-out...

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Unformatted text preview: Lin (cgl286) Homework 1 Lyon (52370) 1 This print-out should have 40 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. This HW assignment is due Feb. 4 by 11PM. 001 10.0 points The part of an element that never changes is its 1. electric charge. 2. atomic mass. 3. atomic number. correct 4. oxidation number. Explanation: 002 10.0 points What is the total mass of the protons in a typical ammonia (NH 3 ) molecule? The mass of a proton is 1 . 673 10- 24 g, of a neutron 1 . 675 10- 24 g, and of an electron 9 . 109 10- 28 g. 1. 9 . 109 10- 27 g 2. 1 . 172 10- 23 g 3. 1 . 675 10- 23 g 4. 1 . 673 10- 23 g correct 5. None of these 6. 1 . 1711 10- 23 g 7. 6 . 3763 10- 27 g Explanation: m p = 1 . 673 10- 24 g m n = 1 . 675 10- 24 g m e = 9 . 109 10- 28 g Number Number Number protons neutrons electrons N 7 7 7 H 3 3 3 HN 3 10 7 10 The total mass of the protons is m = 10(1 . 673 10- 24 g) = 1 . 673 10- 23 g 003 10.0 points How many protons are present in one iron(III) ion? 1. 26 correct 2. 25 3. 27 4. 28 5. 29 Explanation: The atomic number of an element is equal to the number of protons in that elements nucleus. The number of protons defines an el- ement and cannot be changed without chang- ing the element. Iron has an atomic number of 26. 004 10.0 points The atom with 68 neutrons and 50 protons has a mass number of 1. 18. 2. 68. 3. 118. correct 4. Cannot be determined from the informa- tion given. 5. 50. Explanation: Mass number = # p + + # n = 68 + 50 = 118 Lin (cgl286) Homework 1 Lyon (52370) 2 005 10.0 points How many neutrons are in one atom of Cs- 134? 1. 79 correct 2. 2 3. 55 4. 134 Explanation: 006 10.0 points The number of neutrons in an atom of 81 Br is 1. Cannot be determined 2. 35. 3. 81. 4. 116. 5. 46. correct Explanation: For A Z X , A = mass number = # p + + # n and Z = atomic number = # p + . A = 81, so # n = A- # p + = 81- 35 = 46 007 10.0 points The number of fundamental particles in the 160 64 Gd atom is 1. 128 neutrons, 96 protons, and 96 elec- trons. 2. 64 neutrons, 160 protons, and 160 elec- trons. 3. 160 neutrons, 64 protons, and 64 elec- trons. 4. 224 neutrons, 64 protons, and 64 elec- trons. 5. 96 neutrons, 64 protons, and 64 electrons. correct Explanation: The number in the lower left-hand corner to an elements symbol is that elements atomic number; i.e. , its number of protons. The 64 in this example means that Gd has 64 pro- tons. However, for any atom, the number of electrons would be the same if the atom is neutral, it will need to have equal numbers of protons and electrons. The number in the up- per left-hand corner is the mass number of this particular isotope. The mass number is sim- ply the sum of the number of protons (which is fixed) and neutrons (which varies, identify- ing individual isotopes). 64 units of this mass of 160 must be attributable to the protons, so the remaining 96 must be neutrons.the remaining 96 must be neutrons....
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HW1 - Lin(cgl286 Homework 1 Lyon(52370 1 This print-out...

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