JESUDOSS DR. KINGSTON SPRING 2008 THIS EXAM CONSISTS OF 12 QUESTIONS ON 8 PAGES GRADING POINTS 24 pts 17 pts 16 pts 15 pts 12 pts 18 pts 102 pts
CHEM 165 HOUR EXAM III APRIL 2, 2008
NAME______________________ RECIT. INSTR._______________ RECIT. SECT.________________
PAGES Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 TOTAL
SCORE ________ ________ ________ ________ ________ ________ ________
Teaching Assistants and Recitation Sections Name Sections Time Philip Carlson Emily Hull Aaron Kempema Gerald Pollock Selena Russell Stephanie Smith Justin Valenstein 1, 13 6, 12 10, 11 4, 5 8, 9 2, 7 3 9:00, 3:10 2:10, 3:10 1:10, 2:10 12:10, 1:10 10:00, 11:00 10:00, 9:00 11:00
Rules for the Exam: 1. Show all of your work on these exam pages. Numerical answers should be given in the correct number of significant figures and units. Put your answers in the answer spaces. 2. The last page contains some useful information and a periodic table.
CHEM 165 Final Exam: Tuesday, May 6, 7:00 PM 9:00PM Same rooms as hour exams no change
* REGRADE *
Requests for a regrade must be made prior to leaving recitation. Altering answers on an exam prior to submission for a regrade is academic misconduct; such dishonest conduct will be taken very seriously and will be dealt with according to university policy. All regrade requests must be legible.
2 1. (10 pts) Consider the equilibrium associated with the decomposition of ammonia at 600K, 2 NH3(g) N2(g) + 3H2(g) H = 92.6 kJ/mol
For each of the following cases, assume that equilibrium is established at a temperature of 600 K. Circle which way the reaction mixture will shift to establish equilibrium after the change is made: A) Remove NH3(g): B) Increase volume: C) Add H2(g): D) Add a catalyst: E) Reduce T to 500 K: 2. shift toward reactants shift toward reactants shift toward reactants shift toward reactants shift toward reactants shift toward products shift toward products shift toward products shift toward products shift toward products no change no change no change no change no change
(4 pts) What is the conjugate acid of HPO42? Circle the correct answer. A) H3PO4 B) PO43 C) H2PO4 D) HPO4 E) H2O
3.
(4 pts) What is the pH of a 0.015 M solution of Ca(OH)2. A) 12.48 B) 12.18 C) 1.82 D) 1.52 E)
4.
(6 pts) Complete the following table with missing entries: (report your answers in correct number of significant figures) [H+] M [OH-] M pH pOH Acidic or Basic?
1.74 10-6 M (Use this space for your work).
3 5. Consider an aqueous solution of Hydrocyanic acid (HCN). A) (3 pts) Write a balanced chemical equation showing the principle equilibrium involved in the dissociation of HCN in water. (Remember to show phases)
B) (12 pts) Calculate the pH of an aqueous solution of 1.5 10-2 M HCN. Ka for HCN is 4.9 1010 at 25C. (Show all of your work including ICE table and report the answer to the correct number of significant figures.)
Answer: _______________. C) (2 pts) What is the percent ionization of the hydrocyanic acid solution described in part-b? (For full credit, show all of your work and report the final answer to the correct number of significant figures.)
Answer: _______________.
4 6. (8 pts) Calculate the numerical value of the equilibrium constant Kp for the reaction SO2(g) +
1 O2(g) 2
SO3(g)
Kp' = ? is 5.0 10-2 at 302oC.
if the equilibrium constant Kp for 2SO3(g) 2SO2(g) + O2(g) (Show your work for full credit)
Answer: _______________. 7. (8 pts) Consider the following equilibrium reaction at 100oC : COCl2(g) CO(g) + Cl2(g) Kc = 2.19 10-10 A) Suppose a mixture of COCl2 (0.100 M) , CO (1.48 10-6 M) and Cl2 (1.48 10-6 M) were introduced in to a closed vessel at 100oC, predict whether the reaction mixture is already at equilibrium? (Show your work in the space below for full credit)
Check the box.
Yes, it is at equilibrium
No, it is not at equilibrium
B) If the reaction mixture is at not equilibrium, which direction that the must reaction proceed to achieve the equilibrium?
Towards the products (right)
Towards the reactant (left)
5 8. A two step mechanism was proposed to explain the formation of NO2F from the reaction of NO2 and F2. Step 1: Step 2: NO2(g) + F2(g) NO2F(g) + F(g) NO2(g) + F(g) NO2F(g) (fast) (slow)
A) (3 pts) Write the complete and balanced overall reaction.
B) (12 pts) Write the rate law for the reaction assuming that the above mechanism is consistent with the
kinetic data. (Show your work for full credit)
6 9. (12 pts) Consider the equilibrium reaction H2(g) + I2(g) 2HI(g) Kp = 54.5 at 475oC. If a
closed vessel at 475oC was introduced with the initial pressures of 1.5 atm of H2 and 1.5 atm of I2, calculate the equilibrium partial pressures of H2, I2 and HI. (Show your work for full credit)
H2(g) (atm) Initial Change Equilibrium I2(g) (atm) HI(g) (atm)
Write your answers in the box provided below:
H2(g) (atm) Equilibrium Pressures I2(g) (atm) HI(g) (atm)
7 10. (4 pts) At 25oC, the Ka for hydrofluoric acid is 7.1 10-4. Calculate the Kb for the conjugate base of hydrofluoric acid at 25oC. (Show work and report your answers in correct number of significant figures)
11.
Radioactive decay is an example of a first order process. Radioactive Cobalt-60 (60Co) isotope has a half-life of 5.27 years. (Show work and report your answers in proper units and correct number of significant figures) (a) (4 pts) Calculate the rate constant for the nuclear decay of Cobalt-60 isotope.
Answer: _______________. (b) (8 pts) Suppose a hospital bought a sample of 50.0 g of 60Co isotope for its department of radiology, what would be the amount of 60Co isotope (in grams) left after 12 years?
Answer: _______________. 12. Extra credits! (2 pts) The pH of blood is maintained within a narrow range between pH 7.35 and 7.45, by the bicarbonate buffer system through the amount of CO2 in the blood (see equilibrium below). CO2(aq) + 2 H2O(l) HCO3(aq) + H3O+(aq)
How will the pH change with hyperventilation, during which the concentration of CO2(aq) decreases? (Hint: think of Le Chtelier's principle) A) decrease B) increase C) no change D) Need more data to predict
8
Some equations and data that you may or may not need!!
f = eEa/RT k=Ae
Ea/RT
Ea ln k = RT + ln A k1 Ea 1 1 ln k2 = R T2 T1 Kp = Kc.(RT)n R = 0.0821 L.atm/mol.K = 8.314 J/mol.K 0oC = 273 K
Order of the reaction 0 1 2
Integrated Rate Law [A]t = [A]0 kt ln[A]t = ln[A]0 kt
Half-Life
t 1/2 = [A]0 2k
t 1/2 =
0.693 k
1 1 = + kt [ A]t [ A]0
t 1/2 =
1 k[A]0
Solution for a quadratic equation: x =
! b b 2 - 4ac 2a
Periodic Table of the Elements
1A 1 1 H 1.01 3 Li 6.94 11 Na 23.0 19 K 39.1 37 Rb 85.5 55 Cs 133 87 Fr (223) 2A 2 4 Be 9.01 12 Mg 24.3 20 Ca 40.1 38 Sr 87.6 56 Ba 137 88 Ra 226 3B 3 21 Sc 45.0 4B 4 22 Ti 47.9 5B 5 23 V 50.9 41 Nb 92.9 73 Ta 181 6B 6 24 Cr 52.0 42 Mo 95.9 74 W 184 7B 7 25 Mn 54.9 43 Tc (98) 75 Re 186 8 26 Fe 55.8 44 Ru 101 76 Os 190 3A 13 5 B 10.8 10 28 Ni 58.7 46 Pd 106 78 Pt 195 1B 11 29 Cu 63.5 47 Ag 108 79 Au 197 2B 12 30 Zn 65.4 48 Cd 112 80 Hg 201 13 Al 27.0 31 Ga 69.7 49 In 115 81 Tl 204 4A 14 6 C 12.0 5A 15 7 N 14.0 6A 16 8 O 16.0 16 S 32.1 34 Se 79.0 52 Te 128 7A 17 8A 18 2 He 4.00
8B
9 27 Co 58.9 45 Rh 103 77 Ir 192
15 14 P Si 28.1 31.0 33 32 As Ge 72.6 74.9 50 Sn 119 82 Pb 207 51 Sb 122 83 Bi 209
9 10 F Ne 19.0 20.2 18 17 Ar Cl 35.5 39.9 36 35 Kr Br 79.9 83.8 54 53 Xe I 127 131
39 40 Y Zr 88.9 91.2 57 La 139 72 Hf 178
85 86 84 At Rn Po (209) (210) (222)
89 104 105 106 107 108 109 110 Ac Rf Db Sg Bh Hs Mt Ds 227 (261) (262) (263) (262) (265) (266) (281)
Lanthanides
58 Ce 140 90 Th 232
59 Pr 141 91 Pa 231
Actinides
60 61 62 63 64 65 66 67 68 69 70 71 Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 144 (145) 150 152 157 159 162 165 167 169 173 175 92 93 94 95 96 97 98 99 100 101 102 103 U Np Pu Am Cm Bk Cf Es Fm Md No Lr 238 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (260)