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F04_E1A - Chemistry 111 Page 1 out of 5 Exam I Fall 2004...

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Chemistry 111 Page 1 out of 5 Exam I / Fall 2004 Answer Key Show all your work in the space provided in order to receive any credit at all! 1. Which of the following is the formula for potassium permanganate? (02 pts) a) PMnO 2 . b) KMnO 2 . c) PMnO 4 . d) KMnO 4 . e) K 2 MnO 4 . 2. Name the following compound: SO 3 . Sulfur Trioxide . (02 pts) 3. A certain sample of carbon graphite has 3.21 × 10 22 carbon atoms. What is the mass of this sample? (06 pts) This is a simple conversion from atoms to moles to number of grams… 3.21#10 22 C atoms # 6.022 #10 23 C atoms 1mol C # 1mol C 12.011g C = 0.640 g of C graphite. 4. How many oxygen atoms are there is a 22.22 g sample of Na 2 CO 3 (MW = 105.98)? (08 pts) This is similar to the previous question, but we are asking about number of O atoms, not sodium carbonate “molecules”. Therefore, 22.22 g Na 2 CO 3 # 105.98 g Na 2 CO 3 1mol Na 2 CO 3 # 1mol Na 2 CO 3 3 mol O # 1mol O 6.022 # 10 23 atoms = 3.789 × 10 23 O atoms . 5. An isotope of Calcium has a mass number of 45 and a charge of +2. This isotopic ion has 18 electrons, 20 protons, and 25 neutrons. (06 pts) Calcium is element #20, therefore it has 20 protons. Since the mass number is 45, then it must have (the difference) 25 neutrons. Finally, a charge of plus two tells us that it is missing two electrons. Therefore, it must have 18 electrons. 6. When the following operation is performed properly, we end up with 2 significant figures in the answer.
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