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Week 2 Key Practice Problems

Week 2 Key Practice Problems - CHEMISTRY 201X Practice...

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CHEMISTRY 201X August 27-31, 2007 Practice Problems (KEY) (15) Locate the following elements in the Periodic Table; indicate whether it is a metal, metalloid, or nonmetal; identify common charges its ions may adopt. (a) Chromium Transition metal; 2+, 3+, 6+ (b) Xenon Noble gas; 0 (c) Phosphorus Metalloid; 3+. 5+; 3 (d) Zinc Metal; 2+ (e) Arsenic Metalloid; 3+. 5+; 3 (f) Gallium Metal; 3+ (16) Calculate the percentage by mass of the indicated element in the corresponding compound: (a) carbon in ascorbic acid, HC 6 H 7 O 6 ; FW = 176.14 g/mol; % C = 6(12.01 g) / 176.14 g × 100% = 40.91 % C (b) nitrogen in ammonium sulfate; (NH 4 ) 2 SO 4 FW = 132.17 g/mol; % N = 2(14.01 g) / 132.17 g × 100% = 21.20 % N (c) tin in tin(II) fluoride; SnF 2 FW = 156.7 g/mol; % Sn = (118.7 g) / 156.7 g × 100% = 75.75 % Sn (d) sodium in sodium chloride. NaCl FW = 58.44 g/mol; % Na = (22.99 g) / 58.44 g × 100% = 39.34 % Na (17) Determine the empirical and molecular formulas of each of the following substances: (a) Epinephrine, which contains 59.0% C, 7.1% H, 26.2% O and 7.7% N by mass. Its MW is approximately 180 g/mol. Take 100 g. 59.0 g C / 12.01 g/mol = 4.92 mol C 8.92 (9) 7.1 g H / 1.01 g/mol = 7.03 mol H 12.8 (13) 26.2 g O / 16.00 g/mol = 1.64 mol O 2.98 (3) 7.7 g N / 14.01 g/mol = 0.55 mol N (1) C 9 H 13 NO 3
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