1. All the solutions have the same molality. 2. All the solutions have the same molarity.

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Clementine Banks
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1 I. (41 points) A. (12 points) Write your answers on the blanks provided. 1. Which of the following solutes would be more soluble in water? a. CH 3 OH or C 17 H 35 OH b. C 2 H 5 Cl or NaCl c. CHCl 3 or CCl 4 d. C 2 H 5 OH or H 3 C O CH 3 2. What are the optimal pressure (high or low) and temperature (high or low) conditions for dissolving a gas in water? a. pressure b. temperature B. (10 points) Determine whether the statements given below are true or false. Write Y if the statement is true, and N if the statement is false in the blanks provided. Do not usetorf.you should not need to do any calculations for this part. Consider 3 beakers. Each beaker has a solution made up of 1 mol of solute in 100 g of solvent. Each of the solutions has a different density. Beaker 1 has C 2 H 5 OH (ethyl alcohol) in water Beaker 2 has C 12 H 22 O 11 (sugar) in water Beaker 3 has NaCl in water 1. All the solutions have the same molality. 2. All the solutions have the same molarity. 3. Each of the three solutions has a different mass percent of solute. 4. The solutions in Beaker 1 and Beaker 3 have the same boiling point. 5. The solution in Beaker 2 has the lowest freezing point. C. (4 points) What is the boiling point of a 0.33 m solution of benzoic acid in phenol? Pure phenol boils at C and has a boiling point constant of 3.56 C/m. 1

2 D. (6 points) An aqueous solution of urea, CO(NH 2 ) 2 (M = g/mol) is prepared by dissolving g of urea in 456 g of water. 1. What is the mass percent of urea in the solution? 2. What is the molality of the solution. E. (4 points) Consider a m solution of a solute A in water. The density of the solution is 1.12 g/ml. What is the molarity of the solution? F. (5 points) What is the osmotic pressure of M solution of ammonium sulfate? 2

3 II. (42 points) A. (10 points) Consider the reaction 2X+Y Z H < 0 The rate law for the reaction is rate = k [X] [Y] 2 Answer the following questions in the blanks provided. a. What is the order of the reaction with respect to Y? b. What is the overall order of the reaction? c. The rate constant for the reaction at 25 Cis 1.0 L 2 /mol 2 -min. Would you expect the rate constant to increase if the reaction is done at 35 C? d. The rate constant is doubled when substance W is added. W does not get used up by the reaction. What is W called? e. How does W affect the activation energy? B. (15 points) Assume that a molecule A reacts with two B molecules in a one-step process to give AB Write a balanced equation for the reaction. 2. What is the rate law for this reaction? 4. If the initial rate of formation of AB 2 is 2.0 x 10 5 M/sec and the initial concentrations of A and B are 0.30 M, what is the value of the rate constant? 5. What are the units for k? 3

4 C. (9 points) Consider the following first order decompostion of A at a certain temperature. A products It takes 1.00 hour for 75% of A to decompose. 1. What is the half-life of A? 2. What is the rate constant for the decomposiion at that temperature? 3. What is the rate of decomposition at the same temperature when [A] is M? D. (8 points) Consider the following first order reaction at a certain temperature: SO 2 Cl 2 (g) SO 2 (g)+cl 2 (g) The half-life for the reaction at that temperature is 8.0 minutes. How long would it take to reduce the concentration of SO 2 Cl 2 to 1,0% of the original? 4

5 III. (42 points) A. (15 points) Consider the exothermic reaction 2NO(g) + Cl 2 (g) 2 NOCl (g) Which way will the equilibrium shift in response to the following changes? (Answer right, left, more information needed or no effect.) 1. Increased volume? 2. Increased temperature? 3. Increased volume and decreased temperature? 4. NO is added and the temperature is raised? 5. A catalyst is added? B. (8 points) Write a balance equation for the reaction of hydrogen gas with nitrogen dioxide gas to form ammonia gas and steam. Use that equation to write an expression for the equilibrium constant: Equation: Equilibrium constant expression: C. (4 points) 3. At a certain temperature, the following reaction has an equilibrium constant of O 2 (g) 4O 3 (g) What is the value of the equilibrium constant for the reaction below? 2O 3 (g) 3O 2 (g) 5

6 D. (15 points) Consider the following reaction at a certain temperature: SO 2 (g)+no 2 (g) SO 3 (g) + NO (g) 1. Calculate the equilibrium constant for the reaction at that temperature if at equilibrium the partial pressures are P SO2 =P NO2 = 0.50 atm, and P NO =P SO3 = 2.0 atm. 2. Assume that at equilibrium one has the partial pressures of the species given in Part(1). Then suppose enough SO 2 (g) and NO 2 (g) are added to raise both their partial pressures temporarily to 2.00 atm. What are the partial pressures of all species when equilibrium is re-established? To help you, you may fill in the table below. SO 2 NO 2 SO 3 NO P o P P eq P SO2 = P NO2 = P NO = P SO3 6

7 IV. (25 points) A. (15 points) A student dissolves 1.20 g of his unknown in g of tertiary butyl alcohol (TBA). Pure TBA has a freezing point of 24.5 C and a freezing point constant of 8.0 C/m. The solution has a freezing point of 20.5 C. 1. What is the freezing point depression? 2. What is the molality of the solution? 3. How many moles of solute are there in the solution? 4. What is the molar mass of the solute?. 7

8 B. (10 points) In a reaction involving the iodination of acetone, the following volumes were used to make up the reaction mixture: 15.0 ml of 4.0 M acetone 15.0 ml of 1.0 M HCl 10.0 ml of M I ml of H 2 O It takes seconds for the color of the iodine to disappear at 25 C. 1. What is the molarity of the acetone in the reaction mixture? 2. A second reaction mixture is made up where the concentration of I 2 is halved. All other concentrations are the same as in the original mixture. The following volumes were used to make the third reaction mixture: 15.0 ml of 4.0 M acetone 15.0 ml of 1.0 M HCl 5.0 ml of M I ml of H 2 O If the reaction is zero order in I 2, how long will it take the I 2 color to disappear at 25 C for the second reaction mixture? 8

9 BONUS (15 points) All or nothing. The bonus should be done only after you have completed the main part of this exam and checked your work for errors. The time allotted for this exam does not include time for the bonus. Trial and error solutions will not be accepted. Consider 100-proof (50% ethyl alcohol by volume) Scotch whisky. If the temperature were to drop to 10 C, could one still drink the Scotch? (i.e., Show by calculation that the whiskey is a liquid.) The density of ethyl alcohol (C 2 H 5 OH) is 0.79 g/ml. 9

Exam Review. Chapters

Exam Review. Chapters Exam Review Chapters 13 14.2 Chapter 13 Solutions Concepts of: Solution definitions and representations on the macroscopic and particle level Intermolecular forces Concentration units Solubility and temperature