CHEM 108 (Fall-2004) Final Exam (100 pts)

Transcription

1 CHEM 108 (Fall-2004) Final Exam (100 pts) Name: , CLID # LAST NAME, First (Circle the alphabet segment of your LAST NAME): A-B C-F G-L M-O P-Z Please answer the following questions: Part I: Multiple Choices (45 pts: 3 pts each). Circle the ONE best answer: 1. The average normal concentration of Ca 2+ in urine is 5.33 g/l. What concentration of oxalate, C 2 O 4 2- is needed to precipitate calcium oxalate, CaC 2 O 4 (Ksp = 2.3 x 10-9 ) to initiate the formation of a kidney stone? a) 4.3 x b) 1.7 x 10-8 c) 5.5 x 10-8 d) no answer was given 2. When 9 Be is bombarded with α particles, 12 C is formed. What other particle is produced? a) β - b) n c) β + d) P + 3. What is the product formed from 185 Ir by electron capture? a) 184 Os b) c) 185 Os d) 185 Pt 4. Refer to the data given in the information sheet and with the following information: 186 Ir Fe 3+ (aq) + H 2 (g) 2 H + (aq) + Fe 2+ (aq) E cell = 0.77 V Determine E for the reaction: Fe 3+ (aq) + e Fe 2+ (aq) a) 1.54 V b) V c) 0.77 V d) 0.39 V 5. Refer to the data given in the information sheet. Which is the best oxidizing agent? a) O 2 b) Fe 2+ c) F - d) F 2 6. Predict the signs of S, H, and G for the following process (at 25 C): 2 H 2 O (l) 2 H 2 (g) + O 2 (g) S H G a) b) c) d)

2 7. Which of the following aqueous solutions should have the lowest freezing point? a) 0.12 m sugar b) 0.06 m NaCl c) 0.04 m CaCl 2 d) all should have the same freezing point 8. When a solid NH 4 SH is placed in a close flask at 28º C, the solid dissociates according to the equation: NH 4 SH (s) NH 3 (g) + H 2 (g) The total pressure of the equilibrium mixture is atm. Determine K p at this temperature. a) b) c) d) The experimental data from a certain reaction gives these three graphs. What is the most likely order for this reaction? a) zero b) first c) second d) third 10. Which reaction coordinate diagram represents a reaction in which the activation energy, E a is 50 kj/mol and H rxn is -15 kj. a) b) c) d) 2

3 11. Lactic acid, C 3 H 6 O 3, is a weak organic acid present in both sour milk and buttermilk. It is also a product of carbohydrate metabolism and is found in blood after vigorous muscular activity. A buffer is prepared by dissolving 1.00 mol of lactic acid, HLac (K a = 1.4 x 10-4 ) and 1.00 mol of sodium lactate, NaLac, in enough water to form 550. ml of solution. Calculate the ph of this solution. a) 3.85 b) c) 0.0 d) Consider the reaction: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) H = -198 kj The concentration of O 2 (g) at equilibrium increases if a) SO 2 is added to the system b) The temperature of the system is lowered c) SO 3 is added to the system d) increasing the pressure of the reaction 13. Initial rate data were obtained for the following reaction: H 2 (g) + Cl 2 (g) 2 HCl (g) Expt No. Initial [H 2 ], M Initial [Cl 2 ], M Initial Rate, M.s x x x x 10-3 What is the rate law for the reaction? a) Rate = k [Cl 2 ] 2 b) Rate = k[h 2 ] c) Rate = k[cl 2 ] d) Rate = k[h 2 ][Cl 2 ] 14. Calculate the ph after 10.0 ml of 0.40 M HCl is added to 20.0 ml of 0.50 M NaOH. a) 7.00 b) 0.40 c) d) Consider 0.10 M solutions of the following substances. Which would have the highest ph? a) NaCl b) NH 4 NO 3 c) HCN d) Na 2 CO 3 3

4 Part II (22 pts) 1. (12 pts: p pts) The following figure depicts the electrochemical cell for the reaction. 2 Ag + (aq) + Pb (s) 2 Ag (s) + Pb 2+ (aq) a) (6 pts) Label the components of the cell (anode, cathode, flow of electrons and direction of anions) and sketch the reaction (oxidation & reduction) at each electrode b) (6 pts) Using the standard electrode potentials given in the data sheet, calculate E cell and G cell. E cell = V G cell = 2. (10 pts: 2 pts): Fill the blanks a) H and G become equal at K. b) G and G are equal when Q = c) The solubility product for CaF 2 is evaluated by the expression K sp = d) The equilibrium constant for the reaction 2 C (s) + O 2 (g) 2 CO 2 (g) is evaluated by the expression K = e) In the nuclear decay of 222 Rn X + 4 He, X is identified as

5 Part III (36 pts: 6 pts each) Calculations: Show all work for full credit. Please express all answers with proper units and correct number of significant figures. 1. For how many minutes must the electrolysis of a solution containing Au 3+ (aq) be carried out with a current of 3.55 A to deposit 1.00 g Au at the cathode {Au 3+ (aq) + 3 e Au(s)}? 6.90 min 2. For the following reaction at 298 K: 2 HI (g) + Cl 2 (g) 2 HCl (g) + I 2 (s) HI (g) Cl 2 (g) HCl (g) I 2 (s) H f (kj/mol) S (J/K.mol) a) Calculate G in kilojoules G rxn (kj) b) Is the calculated entropy change consistent with what you expected? Why? c) Calculate the equilibrium constant for the reaction at 298 K. K = 5

6 3. A solution of urea, (NH 2 ) 2 CO that is 15% by mass has a density of 1.12 g/ml. Calculate the molarity and the molality of this solution. Molarity = Molality = 4. Determine the molar mass of a compound if a solution of 1.00 g in 225 g of cyclohexane freezes at 6.02 C. Pure cyclohexane freezes at 6.5 C and has a K f = 20.2 C/m. Molar mass = 190 g/mol 6

7 5. Aspirin is a weak organic acid whose molecular formula may be written as HC 9 H 7 O 4 (molar mass = g/mol). A water solution of aspirin is prepared by dissolving 3.60 g per liter. The ph of this solution was found to be Calculate K a for aspirin and % ionization. Ka = 3.6 x 10-4 % ionization = In the titration of 20.0 ml of M HOBr (K a = 2.5 x 10-9 ) with M NaOH, what is the ph at the equivalence point? ph =

8 PREFERENCE SHEET FOR CHEM 108 Final Exam Fall 2004 You will have 140 minutes to complete this exam. The exam has 7 pages plus Periodic Table and Reference page. When you are told to do so, tear off the Periodic Table cover sheet and use as required during exam. Useful Information: Gas Constant: R = J/K.mol = x 10-3 kj/k.mol = L atm/mol.k K = C 1 atm = 760 torr = 760 mmhg Standard temperature = K Faraday`s constant, F = 9.65 x 10 4 C/mol = 9.65 x 10 4 J/K.mol 1 V = 1 J.C -1 Standard electrode potential at 25 C Fe 2+ (aq) + 2e Fe (s) E = V Pb 2+ (aq) + 2e Pb (s) E = V 2 H + (aq) + 2e H 2 (g) E = 0.0 V Ag + (aq) + e Ag (s) E = V O H e 2 H 2 O E = V Cl 2 (g) + 2e 2 Cl - (aq) E = V F 2 (g) + 2e 2 F - (aq) E = V Useful Equations: d (density) = mass (m)/volume (V) PV = nrt π = MRT T = i. Km. P solv = χ solv.p o solv. Rate = k[a] ln [A] o = kt ln[a] = - kt + ln[a] o t 1/2 = ln 2/k = 0.693/k [A] Rate = k[a] 2 1/[A] - 1/[A] o = kt t 1/2 = 1/k[A] o Rate = k [A] = - kt + [A] o t 1/2 = [A] o /2k k = Ae -E a/rt ln k = (-E a /R)(1/T) + ln A G = H - T S G rxn = - nfe = - RTlnK E = ( V/n) ln K (at 25 C) Nernst Equations: G rxn = G rxn + RTlnQ & E cell = E cell - ( V/n) ln Q (at 25 C) G rxn = G rxn + RTlnK Charge (coulombs, C) = current (A) x time (s) 8

9 9 1 1 H 1.01 Periodic Table of the Elements 2 He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc (98) 44 Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po (209) 85 At (210) 86 Rn (222) 7 87 Fr (223) 88 Ra Ac Rf (261) 105 Db (262) 106 Sg (263) 107 Bh (262) 108 Hs (265) 109 Mt (266) 110 Uun (269) 111 Uuu (272) 112 Uub (277) 58 Ce Pr Nd Pm (145) 62 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (260)

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