Name Student ID # CHEMISTRY 122 [Tyvoll] PRACTICE EXAM II Spring 2008 1 2 3 4 5 Possibly Useful Information: 1) ( ) ( ) ( ) ( ) ( ) d (H 2 O) = 1.00 g/ml 2) ( ) ( ) ( ) ( ) ( ) R = 0.0821 L atm/mol K 3) ( ) ( ) ( ) ( ) ( ) N = 6.022 x 10 23 c = 3.0 x10 8 m/s 4) ( ) ( ) ( ) ( ) ( ) h = 6.63 x 10-34 J s 5) ( ) ( ) ( ) ( ) ( ) 1 W = 1 J/s 1 calorie = 4.184 J 6) ( ) ( ) ( ) ( ) ( ) 1 L = 1000 cm 3 7) ( ) ( ) ( ) ( ) ( ) c(h 2 O) = 4.184 J/g 0 C 8) ( ) ( ) ( ) ( ) ( ) K P = K C (RT) Δn(gas) 9) ( ) ( ) ( ) ( ) ( ) 10) ( ) ( ) ( ) ( ) ( ) 11) ( ) ( ) ( ) ( ) ( ) 12) ( ) ( ) ( ) ( ) ( ) 13) ( ) ( ) ( ) ( ) ( ) 14) ( ) ( ) ( ) ( ) ( ) 15) ( ) ( ) ( ) ( ) ( ) Points Missed: Part I Part II Grade (100 Points Possible)
Chemistry 122 (Tyvoll) PRACTICE EXAM II Spring 2008 Name (Please neatly print your name in the space above) Part I. Multiple Choice (3 points each -- Total points = 45) 1. Which of the following hypothetical steps is predicted to be exothermic? 1. pure solvent separated solvent molecules 2. pure solute separated solute molecules 3. separated solvent and solute molecules solution. 4. pure solvent and pure solute heterogeneous mixture 5. not enough information is provided to answer this question 2. Calculate the molality of methanol in a solution prepared by dissolving 59.3 g methanol, CH 3 OH, (32.04 g/mol) in 150 g ethanol. 1. 19.8 m 4. 0.0123 m 2. 0.0156 m 5. 12.3 m 3. 15.6 m 3. Consider the reaction A 2 B, where the value of K C is 1.4 10 8. Which statement about the system at equilibrium is correct? 1. The amount of A is very close to the amount of B. 2. The amount of A is slightly less than the amount of B. 3. The amount of A is much larger than the amount of B. 4. The amount of A is much less than the amount of B. 5. More information is needed to answer the question. 4. Consider the equilibrium reaction, N 2 (g) + 3 F 2 (g) 2 NF 3 (g) In a particular experiment, the following concentrations are found at equilibrium: [N 2 ] is 0.048 M, [F 2 ] is 0.093 M, and [NF 3 ] is 6.55 10-5 M. What is the value of the equilibrium constant? 1. 5.33 4. 2.2 10-36 2. 0.0147 5. 9.0 10 3 3. 1.1 10-4 5. What is the mole fraction of biphenyl, C 12 H 10 (154.2 g/mol), in a 0.555 m C 12 H 10 solution in benzene, C 6 H 6 (78.1 g/mol)? 1. 0.0416 4. 0.555 2. 0.0434 5. 0.0445 3. 0.445 2
6. At 1123 K, a dynamic equilibrium exists between carbon monoxide, carbon dioxide and solid carbon: C (s) + CO 2 (g) 2 CO (g) ΔH = + 172.5 kj If K C = 0.153, what is the value of K p for this reaction? 1. K p = 0.153 4. K p = 1.66 x 10-3 2. K p = 10.7 5. K p = 14.1 3. K p = 7.09 x 10-2 7. Predict which one of the following pairs of compounds would form a solution. 1. Solute: KI Solvent: CCl 4 2. Solute: CH 3 OH Solvent: CCl 4 3. Solute: CCl 4 Solvent: CH 3 CH 2 OH 4. Solute: CH 3 (CH 2 ) 8 CH 2 OH Solvent: H 2 O 5. Solute: CH 2 Cl 2 Solvent: CH 3 (CH 2 ) 8 CH 3 8. Which one of the following best describes what occurs in a reaction system when it reaches a state of dynamic equilibrium? 1. all concentrations of reactants and products are the same 2. the sum of the reactant concentrations equals the sum of the product concentrations 3. the number of collisions per unit time is the same for all species present 4. the rates for both forward and reverse reaction processes are the same 9. Which of the following solutions has the lowest freezing point? 1. 1.0 m glucose in water 4. 1.0 m NaHSO 4 in water 2. 1.0 m NaCl in water 5. pure water 3. 1.0 m Na 2 SO 4 in water 10. Identify the acids/bases on respective sides of the equation: HCO 3 1- + OH 1- CO 3 2- + H 2 O 1. acid + base acid + base 4. acid + base base + acid 2. base + acid acid + base 5. acid + acid base + base 3. base + acid base + acid 11. Which of the following is not true in a dynamic equilibrium describing a saturated solution? 1. Solid crystallizes from solution. 2. Solid dissolves into solution. 3. Concentration of dissolved solute remains constant. 4. Quantity of un-dissolved solute remains constant. 5. Rate of dissolving is double the rate of crystallization. 3
12. The greatest gas solubility in water is predicted under what conditions? 1. high T, high partial pressure 2. high T, low P. 3. low T, low P 4. low T, high P 5. solubility of gases cannot be predicted. 13. The conjugate acid of H 2 PO 4 is 3 1. PO 4 2 2. H 2 PO 4 3. H 2 PO 4 4. H 3 PO 4 + 5. H 3 PO 4 14. Which one of the following is the weakest acid? 1. HF 3. HBr 2. HCl 4. HI 15. What is the total number of moles of ions in 0.250 L of 0.391 M Na 2 CO 3, a strong electrolyte? 1. 0.391 mol 4. 0.196 mol 2. 0.0978 mol 5. 0.587 mol 3. 0.293 mol 4
Part II - Total points = 55. Answer each of the following questions. SHOW ALL WORK! 1. (10 points) Osmotic pressure measurements are routinely used in the determination of molecular weights for high molecular proteins. An African swine fever virus-induced protein (p12) was studied in virus-infected Vero cells using the monoclonal antibody 18B.B11. If an aqueous solution containing 539 mg of p12 protein per 100 ml at 25 0 C has an osmotic pressure of 8.35 mmhg, calculate the molar mass of the p12 protein in g/mol and in kda if 1 Dalton (Da) = 1 g/mol. 1 atm = 760 mmhg You must show all work for credit or partial credit! 5
2. (10 points) At high temperatures, like those found in internal combustion automobile engines, N 2 reacts with O 2 to produce NO (g), a primary air pollutant. Consider this reaction, at 2300 K where, N 2 (g) + O 2 (g) 2 NO (g) K C = 1.7 x 10-3 If 0.300 mol NO (g) are placed into a 20.0 L reaction vessel and heated to 2300 K, calculate the equilibrium concentrations of all three species (N 2, O 2 and NO). Show all work, including the appropriate ICE table, for credit! Is this reaction reactant-favored or product-favored at 2300 K? Explain briefly. 6
3. (10 points) When 1.50 g of a newly synthesized, molecular, nonelectrolyte compound were dissolved in exactly 75.0 g of hexane, C 6 H 14, the freezing point of the solution was lowered from 6.50 0 C (pure hexane) to 2.70 0 C for the solution. For hexane, K f = 20.2 0 C/molal. (a) Calculate the molality of the solution. Show all work for partial credit! (b) Calculate the molar mass of the solute. Show all work for partial credit! 7
4. (10 points) Consider the reaction in which 2 NH 3 ( g) N 2 (g) + 3 H 2 (g), where ΔH = + 92.2.28 kj at 298 K. If N 2 (g), H 2 (g) and NH 3 (g) are initially in equilibrium in a reaction vessel, how will each of the following changes affect the equilibrium concentrations shown below? Assume constant volume except for the last case. Answer the question by writing I (increase), D (decrease) or NC (no change) in each of the blanks provided. Change [NH 3 ] [H 2 ] K C Some H 2 is removed from the container The temperature is increased The pressure of the NH 3 is decreased The volume of the container is increased 5. (10 points) Hydrogen gas can be generated at room temperature (298 K) in a reaction between methane gas and water vapor: CH 4 (g) + H 2 O (g) CO ( g) + 3 H 2 (g), where K C = 0.94. If the initial concentrations of the gaseous species are [CH 4 ] = 0.100 M, [H 2 O] = 0.100 M, [CO] = 0.0500 M and [H 2 ] = 0.200 M, will more H 2 be formed, will it decompose to make more CH 4 and H 2 O once the mixture achieves equilibrium at 2300 K, or is the system already at equilibrium? Make the appropriate calculations and then clearly discuss your results for credit on this question. 8
6. (5 points) According one text, a 0.92% (w/v) NaCl (0.16 M) solution is isotonic with the fluid in red blood cells. Another solution used, D5W, is 5.5% (w/v) solution (0.31 M) of glucose in water and is also isotonic with the fluid in red blood cells. Explain how these solutions can have such different concentrations and still both be isotonic with the fluid in red blood cells. Also explain what might happen if the concentration of NaCl in such a saline solution that was in contact with red blood cells was less than 0.92%. You must be complete and specific to receive credit on these questions! 9