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midterm2withanswers - Chem. 33 2nd Midterm SOLUTION SHEET...

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SOLUTION SHEET 1 of 6 Chem. 33 2 nd Midterm Date: Nov. 9, 2007 Student name: ___________________ Student SISD #: __________________ Maximum number of points: 10 1. (2 point) A mixture contains only NaCl and Fe(NO 3 ) 3 . A 0.456-g sample of the mixture is dissolved in water, and an excess of NaOH is added, producing a precipitate of Fe(OH) 3 by the following reaction: F e 3+ (aq) + 3 OH - (aq) Fe(OH) 3 (s) The precipitate is filtered, dried, and weighed. Its mass is 0.107 g. Calculate the following: a. the mass of iron in the sample b. the mass of Fe(NO 3 ) 3 in the sample ANSWER: a) Fe 3+ (aq) + 3 OH - (aq) Fe(OH) 3 (s) Fe(OH) 3 : 55.85 + 3(16.00) + 3(1.008) = 106.87 g/mol Fe g g 0559 . 0 Fe(OH) g 106.9 Fe g 55.85 x Fe(OH) 107 . 0 3 3 = b) Fe(NO 3 ) 3 : 55.85 + 3(14.01) + 9(16.00) = 241.86 g/mol 3 3 3 3 ) ( 242 . 0 Fe g 55.85 ) Fe(NO g 241.9 x 0559 . 0 NO Fe g Fe g =
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SOLUTION SHEET 2 of 6 2. (3 points) A buffer solution is prepared by dissolving 1 mole of formic acid (HCOOH, pKa = 3.75) and 1 mole of sodium formate (HCOONa) in enough water to make 1 L. a. Calculate the pH of this solution. b. 100 mL of a 1 M solution of HCl is added to the buffer solution. What is the pH? c.
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midterm2withanswers - Chem. 33 2nd Midterm SOLUTION SHEET...

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