Chem 204 Spring 2014 Name PRACTICE EXAM I. There are 9 pages (counting this one) and a periodic table.

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1 Chem 204 Spring 2014 ame TA/Section PRACTICE EXAM I This Examination is worth 100 points. There are 9 pages (counting this one) and a periodic table. o books, notes, cellphones, anything with earbuds/earphones, or laptops; you may only have out pencils or pens and a scientific calculator. Write directly on the exam. You have two hours to complete this exam. You may leave early if you are done early. When you turn your exam in, you must show your university ID card to the proctor/ta. Constants and conversions that you might need are given on the next page. Good luck! 1

2 Constants and Conversions A = Avogadro's number = x mol -1 h = x J s c = 3.00 x 10 8 m s -1 charge on one electron = e = x C ε0 = x C 2 J -1 m -1 me = mass of electron = x kg 1 atomic mass unit = x kg k = k B = Boltzmann s constant = x J K -1 1 cm -1 = x J R = L atm K -1 mol -1 = J K -1 mol -1 1 ev = x J K = C 1 J = 1 kg m 2 s -2 z = hertz = s torr = 1 atm = 14.7 psi = bar = mb 1000 L = 1 m 3 Formulas (P + a(n 2 /V 2 )) (V - nb) = nrt ln (P) = - vap /RT + S vap /R ln(p 2 /P 1 ) = ( vap /R) [(1/T 1 ) (1/T 2 )] -b ± b 2-4ac x = for ax 2 + bx + c = 0 2a Equilibrium Constants at 25 C AgCl: Ksp = 1.6 x AgBr: Ksp = 7.7 x AgI: Ksp = 1.5 x

3 I. (60 points). Multiple Choice. Circle the letter of the best answer. 5 points each. o partial credit. 1. Ammonia, 3, is a gas at P = 1 atm, T = 25 C. Ammonia can be liquefied at C (P = 1 atm). Methylamine, C 3 2, is also a gas at P = 1 atm, T = 25 C. Methylamine can be liquefied at -6.4 C (P = 1 atm). What do these experimental data tell us about these molecules? a. Methylamine is not as good at hydrogen bonding as ammonia. b. The London dispersion interactions between methylamine molecules must be larger than those between ammonia molecules. c. It must be easier to achieve a supercritical fluid state for methylamine compared to ammonia. d. If you were to liquefy methylamine and ammonia and cool them both to T = -50 C (P = 1 atm), methylamine would have the higher vapor pressure. e. The polarizabilities of these molecules are the same. f. More than one of the above. g. one of the above. 2. Can one 2 S molecule hydrogen-bond to another 2 S molecule? a. o. b. Yes. 3. Which of the molecules below is the most lipophilic? Circle the whole molecule. C 2 2 C C C 2 C 3

4 4. Which of the molecules below has the largest Kow? Circle the whole molecule. C 2 2 C C C 2 C 5. True or false: The enthalpy change for the process of liquid vaporization ( A(l) à A (g) ) will almost always be negative. a. True. b. False. 6. You take 10.0 grams of solid copper(ii) phosphate, Cu3(P4) 2, and put it in a beaker. You add ml of water to the beaker at T = 298 K. The solid does not appear to dissolve. You wait a long time and eventually measure the equilibrium concentration of Cu 2+ (aq) in the water to be 5.01 x 10-8 M. What is the Ksp of copper(ii) phosphate? a x10-8 b x10-14 c x10-15 d x10-37 e x10-37 f x10-37 g x10-43 h x10-43 i x10-44 j x

5 7. The approximate strength of an average hydrogen bond is a. 2 kj/mol b. 20 kj/mol c. 200 kj/mol d kj/mol 8. CdS is a semiconductor that has a bandgap of 2.4 ev. What is the longest wavelength of light that CdS can absorb? a. 517 nm b nm c nm d. 1.5 x10 19 nm e. 1.3 x nm 9. The enry s Law constant for nitrogen in water, at 20 C, is 7.0 x 10-4 mol L -1 atm -1. The enry s Law constant for helium in water, at 20 C, is 3.7 x 10-4 mol L -1 atm -1. Which gas is more soluble in water at 20 C? a. nitrogen b. helium c. These numbers cannot tell you anything about solubility. 10. Vegard s Law says what? a. The partial pressure of a gas over a liquid determines the density of the solution. b. The structural properties of a solid solution are a linear function of the composition of the solution. c. The solubility of one metal in another is determined by the metallic radii. d. The further down the periodic table you go, the larger the bandgap for semiconductors. 11. If you mix 5.00 ml of 1.25 x M Ag 3 with 5.00 ml of 2.50 x 10-4 M ai at 25 C, will anything precipitate? a. Yes. b. o. c. ow am I supposed to figure that out?? 12. Which one of the following statements about metals is TRUE? a. Solid solutions of metals are called alloys. b. Metals are characterized by a partially filled electronic band. c. The properties of solid solutions of metals can be quite different from the pure metals alone. d. All of the above are true. e. one of the above are true. 5

6 For the remainder of the exam: you must show clear work in order to earn any partial credit. II. (10 points). The freezing point of pure water is 0.00 C, and the freezing point of pure benzene is 5.5 C. When a 5.00% by mass solution of acetic acid, C 3 C, is made in water, the freezing point of the solution is 1.72 C. When a 5.00% by mass solution of acetic acid is made in benzene, the freezing point of the solution is 3.18 C. The k f for water is 1.86 K kg mol 1, and k f for benzene is 5.12 K kg mol 1. (a) What is the experimentally-determined molecular weight (molar mass) of acetic acid from the aqueous solution data? (b) What is the experimentally-determined molecular weight of acetic acid from the benzene data? (c) Compare your answers from (a) and (b) to the theoretical molecular weight of acetic acid. Suggest an explanation for the behavior of acetic acid in water vs. benzene. (int: draw molecular structures). 6

7 III. (10 points). The vapor pressure of chlorine dioxide, Cl 2, is 155 torr at C and 485 torr at 0.00 C. What is the normal boiling point of Cl 2? 7

8 IV. (5 points). ormal fish need a minimum of 4 mg of 2 gas per liter of water in order to survive. You are working in a biology lab, trying to create genetically engineered fish that can survive on even less oxygen. You have a 500 L tank of water, at T = 298 K and normal 1.00 atm pressure, from which you evacuate all the air. Then you bubble in one liter of 2 into the tank, put your mutant fish in the tank, and are delighted to see that they are swimming around. Should you be so happy? Do the calculation to see if your mutant fish really are surviving on less oxygen than normal fish. V. (5 points). List the relevant characteristics a molecule must have, if it were to be a good drug candidate according to the Rule of Five. 8

9 VI. (5 points). Draw a graph that shows how the potential energy of intermolecular interactions between two molecules depends on distance. VII. (5 points). You acquire the ultraviolet-visible spectrum of an interesting dye molecule in solution. The spectrum is shown below. Given that the experiment was done in a 1-cm cuvette and that the extinction coefficient for the dye is 12,375 M -1 cm -1 at 540 nm, calculate the concentration of the dye in solution. 9

Chem 204 Spring 2014 Name PRACTICE EXAM II. There are 9 pages (counting this one) and a periodic table.

Chem 204 Spring 2014 Name PRACTICE EXAM II. There are 9 pages (counting this one) and a periodic table. Chem 204 Spring 2014 ame TA/Section PRACTICE EXAM II This Examination is worth 100 points. There are 9 pages (counting this one) and a periodic table. o books, notes, cellphones, anything with earbuds/earphones,