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CHM1046 Spring 2008 Practice Exam II KEY_1

CHM1046 Spring 2008 Practice Exam II KEY_1 - CHM1046 Spring...

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CHM1046 Spring 2008 Practice Exam II KEY Show all work for full credit; Circle or write in final answers when appropriate. Name: ______________________________ Rec. Sec#: _____________ 1) What is the molality of 13.82% by mass sulfuric acid? The molar mass of H 2 SO 4 is 98.08 g/mol. Answer: ___ c ________ a. 0.1409 m 13.82% is 13.82 g H 2 SO 4 /100g solution b. 1.409 m Divide 13.82 g/98.08 g/mol = 0.1409mol c. 1.635 m m is in mol solute/kg solvent and 100g solution is 86.18g d. 13.55 m solvent and 13.82g solute. e. 15.73 m m = 0.1409 mol H 2 SO 4 /86.18g solvent = 1.635 m 2) Determine the heat of solution of NaOH given the thermodynamic equations below. Na(s) + ½ O 2 (g) + ½ H 2 (g) NaOH(s) H o f = -425.9 kJ/mol Na(s) + ½ O 2 (g) + ½ H 2 (g) NaOH(aq, 1 m ) H o f = -469.2 kJ/mol Answer: _____ b __________ a. -895.1 kJ/mol Want NaOH(s) NaOH(aq, 1 m ) b. -43.3 kJ/mol So –(-425.9 kJ) + -469.2 kJ = -43.3 kJ c. +1.102 kJ/mol d. +43.3 kJ/mol e. +895.1 kJ/mol 3) The Henry’s Law constant for N 2 in water at 37 o C is 8.2 x 10 -7 M/mmHg. What is the equilibrium concentration of N 2 in water when the partial pressure of N 2 is 634 mmHg? Answer: _____ b ________ a. 1.3 x 10 -9 M S g = K H P g = 8.2x10 -7 M/mmHg(634 mmHg) = b. 5.2 x 10 -4 M 5.2 x 10 -4 M c. 1.9 x 10 -2 M d. 1.9 x 10 3 M e. 7.7 x 10 8 M

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4) Ideally, colligative properties depend only on the _________ a __________ a. concentration of solute particles in a solution. b. identity of the solute particles in a solution. c. color of a solution. d. hydrated radii of the molecules or ions dissolved in a solution. e. partial pressure of the gases above the surface of a solution. 5) What is the freezing point of a solution containing 4.78 g of naphthalene (molar mass = 128.2 g/mol) dissolved in 32.0 g paradichlorobenzene? The freezing point of pure paradichlorobenzene is 53.0 o
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