2 - Chem 4 Mandatory Homework Assignment Fall 2009 ANSWERS...

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Chem 4 Mandatory Homework Assignment Fall 2009 ANSWERS Ben’s Section’s Questions: 1BY. (5 pts) The molar mass of element Z in a natural sample is 81.73 g mol –1 . Element Z has THREE naturally occurring isotopes: Z-79 (molar mass 78.9257 g/mol), Z-81 (molar mass 80.9264 g/mol), and Z-83 (molar mass 82.9307 g/mol). It is known that Z-79 is exactly two times more abundant in nature than Z-81. What are the percentage abundances of each of these THREE isotopes? 2BY. (10 pts) In the search for new drugs to treat diseases like cancer and AIDS, medicinal chemists have turned their attention toward derivatives of nucleosides. One such compound, GS1 (MM = 284.29 g/mol), has a ring nitrogen replaced with a sulfur. Analysis of a 115.0 mg sample of GS1 (which contains C, H, N, S and O) showed the presence of 48.58 mg of carbon, 4.88 mg of hydrogen, 22.67 mg of nitrogen and 12.97 mg of sulfur. Determine the empirical and molecular formula of GS1 . 3BY. ( 10 pts ) An analytical chemist mixes 32.0 mL of 0.269 M nickel (II) chloride with 37.0 mL of 0.260 M potassium hydroxide. Write a balanced equation, calculate the maximum number of grams of the solid (if any) that will be formed and the amount (in grams) of the reagent in excess left at the end of the reaction. 4BY. ( 10 pts ) Tetraphosphorous trisulfide can be made by the following reaction: P 4 + S 8 ⎯→ P 4 S 3 ( unbalanced ) If 133 grams of phosphorous (P 4 ) is mixed with 126 grams of sulfur (S 8 ) , how many grams of the product can be formed? How much of which element will be left over? Lee’s Sections’ Questions: 1LH. (5 pts) The molar mass of element Z in a natural sample is 80.73 g mol –1 . Element Z has THREE naturally occurring isotopes: Z-79 (molar mass 78.9257 g/mol), Z-81 (molar mass 80.9264 g/mol), and Z-83 (molar mass 82.9307 g/mol). It is known that Z-79 is exactly two times more abundant in nature than Z-81.
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This note was uploaded on 01/30/2012 for the course CHEM 6A taught by Professor Pomeroy during the Summer '08 term at UCSD.

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2 - Chem 4 Mandatory Homework Assignment Fall 2009 ANSWERS...

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