F03_E1A - Chemistry 111 Page 1 out of 5 Exam I / Fall 2003...

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Chemistry 111 Page 1 out of 5 Exam I / Fall 2003 Answer Key Show all your work in order to receive any credit at all! 1. Name the following compounds. Spelling counts. (02 pts each) a) Ca(MnO 4 ) 2 Calcium permanganate . b) P 4 O 6 Tetraphosphorus hexaoxide . 2. How many hydrogen atoms are there in a 2.34 g sample of phosphoric acid (H 3 PO 4 , MW = 97.99)? (08 pts) This is just a huge conversion factor… 2.34 g H 3 PO 4 × 1 mol H 3 PO 4 97.99 g H 3 PO 4 × 3 mol H 1 mol H 3 PO 4 × 6.022 × 10 23 H atoms 1 mol H = 4.31 × 10 22 H atoms . 3. A 50.0 mL solution of K 3 PO 3 is prepared to be 2.00 M. How many moles of K 3 PO 3 are present in that solution? (06 pts) Very simple question. It is based on the definition of molarity. Remember that… N = M × V 2.00 mol L × 0.0500 L = 0.100 moles . 4. The empirical formula for a certain compound is CH 2 O. If you determine during a colligative properties experiment that the molecular weight of this compound is 180.1, what would be its molecular formula? (04 pts) The empirical weight is approximately 30. How many times can you fit 30 into 180.1? Six times! Therefore, the molecular formula is: C 6 H 12 O 6 .
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Chemistry 111 Page 2 out of 5 Exam I / Fall 2003 Answer Key 5. How many protons, neutrons, and electrons are there in one isotope of 58 Mn +2 ? (06 pts) There are 25 protons, 33 neutrons, and 23 electrons. 6. Look at the calculation shown below. How many significant figures should we have in the answer? (03 pts) 23.45 × 0.055555 97.1 + 5.3 Well, the denominator must be solved first and it is an addition. The rules for addition are different from multiplication and division. Therefore, we check the decimal places.
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This note was uploaded on 02/08/2010 for the course CHEM 111 taught by Professor Kenney during the Spring '08 term at Case Western.

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F03_E1A - Chemistry 111 Page 1 out of 5 Exam I / Fall 2003...

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