Final Exam A - UMass Amherstpeople.umass.edu/ch112sg/Exams/Fall05/F05_Final.pdfChem 112, Fall 05 (Garman/Weis) Name:_____ Final Exam A, 12/20/2005 (P rintC leay)+2points page 1 Before

Chem 112, Fall 05 (Garman/Weis) Name:________________________________ Final Exam A, 12/20/2005 (Print Clearly) +2 points

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Before you begin, make sure that your exam has all 10 pages. There are 24 required problems worth 4 points apiece, unless otherwise noted, and two 4-point extra credit problems. Stay focused, stay calm. Work steadily through your exam. YOU MUST: Put your name and student ID on the bubble sheet correctly. Put all your answers on the bubble sheet; nothing on this exam will be used for grading. Sign the statement on the last page of the exam. Turn in both the exam and bubble sheet when you are done. Good Luck!

TABLES of DATA – All the Necessary Data are Presented with the Problem

Chem 112, Fall 05 (Garman/Weis) Name:________________________________ Final Exam A, 12/20/2005 (Print Clearly)

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Physical Constants & Conversions: Room Temperature = 25°C = 298K T (°C) + 273 = T (K) 1 atm = 760 mm Hg

R = 0.008314 kJ/(K mol) = 8.314 J/(K mol) = 0.0821 (L atm)/(K mol) N = 6.02 x 1023

Kbp for water: +0.512°C/m Kfp for water: -1.86°C/m ∆Hvap = 40.7 kJ/mol for water

F = 96.485 kJ/(mol eV) = 96,485 C/(mol e) 1 C = 1 coulomb

KW = 10-14 at 25°C

Useful Equations: PV = nRT Π = cRT

∆T = Kmi PA = XA PAo k = Ae -Ea/RT

ln(k2/k1) = (Ea/R)(1/T1 - 1/T2) ln(P2/P1) = (ΔH/R)(1/T1 - 1/T2)

A0 - A = kt ln(A/A0) = -kt t1/2 = 0.693/k 1/A - 1/A0 = kt

Kp = Kc(RT)Δn

aA + bB cC + dD Q = ([C]c[D]d)/([A]a[B]b) K = ([C]eqc[D]eq

d)/([A]eqa[B]eq

b)

pH = -log[H3O+] pOH = -log[OH-] pKA = -logKA pKB = -logKB

KW = [H3O+][OH-] KW = KAKB

HA(aq) + H2O(l) A-(aq) + H3O+(l) KA = [H3O+][A-]/[HA]

B(aq) + H2O(l) B+H(aq) + OH-(l) KB = [OH-][B+H]/[B]

pH = pKA + log([conjugate base]/[acid])]

ΔS = qrev/T qrev = ΔHsys (for a constant pressure process) wmax = -ΔGsys

ΔSsys = Σ S(final state) – Σ S(initial state) ΔSuniv = ΔSsurr + ΔSsys

ΔGsys = ΔHsys – TΔSsys ΔGorxn = Σ ΔGo

f (products) – Σ ΔGof (reactants)

ΔG = ΔGo + (RT)lnQ ΔGo = -(RT)lnK

Eocell = Eo

cathode – Eoanode Eo

cell = Eo(reduction ½ rxn) + Eo

(oxidation ½ rxn) (1/2 reactions are expressed as reductions)

E = Eo – (RT/nF)lnQ E = Eo – ((0.0257 V)/n)lnQ (at T = 298 K) Eo = (RT/nF)lnK

wmax = nFE ΔG = -nFE

Current (amperes, A) = [electric charge (coulombs, C)]/[time (seconds, s)]

Electric charge (coulombs, C) = [n (moles of electrons transferred)] x [F (coulombs/mole e-)]


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1. If we look at the halogens in their elemental form, F2 and Cl2 are gases, Br2 is a liquid, and I2 is a solid at 298K. What is responsible for this phenomenon?

A. dipole-dipole interactions increase with molecular size. B. induced dipole-induced dipole interactions increase with molecular size. C. dipole-induced dipole interactions increase with molecular size. D. polarity increases with molecular size. E. both C and D above

2. Determine the heat of vaporization of a pure liquid from the following experiment: A fixed

amount of the liquid is placed in a sealed container and allowed to equilibrate at 250K, where the vapor pressure is measured to be 249 mm Hg. The system is then heated to 500K and allowed to re-equilibrate, when the vapor pressure of the system is measured as 657 mm Hg.

A. 2.02 kJ/mol B. 4.03 kJ/mol C. 11.0 kJ/mol D. 39.8 kJ/mol E. None of the above

3. Which of the following has the lowest boiling point?

A. H2O B. H2S C. H2Se D. H2Te

4. Sodium Chloride (NaCl) is commonly used to melt ice this time of year. If 100 g of NaCl is

added to 3.00 kg of water to a final volume of 3.08 L, what will the melting point of the solution be? The Kmp for water is -1.86°C/m.

A. -1.03°C B. -1.06°C C. -2.07°C D. -2.12°C E. -6.36°C


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5. An unknown amount of glycerol (a non volatile, non-ionic compound with a molecular weight of 92.1 g/mole) is mixed with water to a final volume of 2.00 L. If the osmotic pressure of the solution at room temperature is measured as 3.00 atm, what is the number of moles of glycerol in the solution?

A. 0.00242 moles B. 0.123 moles C. 0.245 moles D. 2.92 moles E. 22.6 moles 6. Ethylene glycol, used to prevent automobile radiators from boiling over in the summer, is a

non-volatile, non-ionic compound with a molecular weight 62.1 g/mole. If 651 g of ethylene glycol is added to 1.50 kg of water, what is the vapor pressure of the solution at 80°C if the vapor pressure of pure water is 355.1 mm Hg at 80°C?

A. 39.7 mm Hg B. 107 mm Hg C. 248 mm Hg D. 315 mm Hg E. None of these 7. How long does it take to completely oxidize 6 beers (2.0 moles of ethanol) if the zero-order

rate constant for the oxidation of ethanol in the liver is 0.00425 M/hour. Assume the volume of fluids in a typical person is 40 L.

A. 5.9 hours B. 8.5 hours C. 12 hours D. 14 hours E. None of these


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8. For the reaction A + 2B + 3C X + 2Y, 8 experiments were performed with different starting concentrations of A, B, and C. The rate of appearance of X is shown: Experiment [A] [B] [C] rate of appearance of X

1 0.100 M 0.100 M 0.100 M 1.72 x 10-4 M/sec 2 0.100 M 0.200 M 0.100 M 3.44 x 10-4 M/sec 3 0.100 M 0.100 M 0.200 M 6.88 x 10-4 M/sec 4 0.100 M 0.200 M 0.200 M 1.38 x 10-3 M/sec 5 0.200 M 0.100 M 0.100 M 1.72 x 10-4 M/sec 6 0.200 M 0.200 M 0.100 M 3.44 x 10-4 M/sec 7 0.200 M 0.100 M 0.200 M 6.88 x 10-4 M/sec 8 0.200 M 0.200 M 0.200 M 1.38 x 10-3 M/sec

What is the rate equation for the reaction?

A. rate = k[A][B][C] B. rate = k[A][B]2[C]3 C. rate = k[B]2[C] D. rate = k[B][C]2 E. None of these

9. Radiocarbon dating is based upon the first-order decay of the 14C isotope, which has a rate

constant of 0.0001203 year-1. How long will it take for 0.200 g of 14C to convert to 0.0250 g? A. 1450 years B. 5760 years C. 17300 years D. 291000 years E. None of these 10. Ammonia is made industrially by combining elemental nitrogen and hydrogen according to

the following reaction at 450°C: N2(g) + 3H2(g) 2 NH3(g) If a reaction container contains 2.00 M N2, 5.00 M H2 and 10.0 M NH3, which way will the reaction shift to reach equilibrium if the Kc for the reaction is 0.16?

A. The reaction will make more NH3 because Q > K. B. The reaction will consume NH3 because Q > K. C. The reaction will make more NH3 because Q < K. D. The reaction will consume NH3 because Q < K. E. [NH3] will remain the same because Q = K.


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11. What is the correct form of the equilibrium constant expression for the reaction PbI2(s) Pb2+(aq) + 2 I-(aq)

A. Kc = [Pb2+][I-] B. Kc = [Pb2+][I-]2 C. Kc = [PbI2] / [Pb2+][I-]2 D. Kc = [Pb2+][I-]2 / [PbI2] E. None of these is correct 12. (5 pts) Nitrogen and oxygen combine at high temperatures to make the pollutant nitrogen

monoxide according to the following reaction: N2(g) + O2(g) 2 NO(g) A reaction vessel initially contains 4.00 M of N2 and 1.00 M of O2. The reaction then proceeds to equilibrium, where the concentration of NO is recorded as 0.0824 M. What is the equilibrium constant Kc for this reaction?

A. 4.47 x 10-4 B. 1.70 x 10-3 C. 1.79 x 10-3 D. 7.16 x 10-3 E. 5.59 x 102

13. The conjugate acid of HSO4

- is ________.

A. OH- B. SO42- C. H2SO4 D. H2O E. H3O+

14. Which one of the following aqueous solutions will have a pH of 10.00 at 25 °C?

A. 0.1 M HCl B. 10-4 M NaNO3 C. 10-4 M HBr D. 10-4 M NaOH E. 1.0 M KOH 15. Which of the following weak acids has the strongest conjugate base in an aqueous solution?

A. acetic acid, Ka = 1.8 × 10-5 B. hydrogen sulfite ion, Ka = 6.2 × 10-8 C. phosphoric acid, Ka = 7.5 × 10-3 D. formic acid, Ka = 1.8 × 10-4 E. nitrous acid, Ka = 4.5 × 10-4


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16. Which of the following combinations would make the best buffer at pH 5.0? KA KB A. H3PO4 and H2PO4

- 7.5 × 10-3 1.3 x 10-12 B. HNO2 and NO2

- 4.5 × 10-4 2.2 x 10-11 C. CH3CO2H and CH3COO- 1.8 × 10-5 5.6 x 10-10 D. H2PO4

- and HPO42- 6.2 × 10-8 1.6 x 10-7

E. NH4+ and NH3 5.7 × 10-10 1.8 x 10-5

17. What is the pH of a buffer that results when 0.50 mole of Na3PO4 is mixed with 0.75 mole of

HCl and diluted with water to 1.00 L? (The acid dissociation constants for phosphoric acid are Ka1 = 7.5 × 10-3, Ka2 = 6.2 × 10-8, and Ka3 = 3.6 × 10-13)

A. 7.03 B. 7.21 C. 7.38 D. 12.27 E. 12.44 18. The Ksp of PbBr2 is 6.6 × 10-6 at 25 °C. What is the concentration of Br- in a saturated

solution of PbBr2(aq)?

A. 3.8 × 10-2 M B. 2.4 × 10-2 M C. 1.9 × 10-2 M D. 1.2 × 10-2 M E. 2.6 × 10-3 M 19. The second law of thermodynamics states that

A. spontaneous reactions are always exothermic. B. energy is conserved in a chemical reaction. C. the Gibbs energy is a function of both enthalpy and entropy. D. ΔS = - ΔH for any chemical reaction. E. in a spontaneous process, the entropy of the universe increases.

20. If a process is exothermic and spontaneous, which of the following must be true?

A. ΔG < 0 and ΔH < 0 B. ΔG > 0 and ΔH < 0 C. ΔG < 0 and ΔS > 0 D. ΔH < 0 and ΔS > 0 E. ΔH > 0 and ΔS < 0


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21. DNA forms a double helix by specific base-pairing interactions. Some short DNA segments (oligonucleotides) can self-dimerize. For example, GAAGCTTC forms dimers reversibly according to the process:

2 GAAGCTTC The equilibrium constant (Keq) and standard state enthalpy (ΔHo

rxn) of dimerization were measured at 37 oC and found to be 7.33 x 104 and -184 kJ/mol, respectively. What is ΔSo

rxn?

A. -687 J/K B. -594 J/K C. -524 J/K D. -500 J/K E. 524 J/K 22. Write a balanced chemical equation for the following reaction in an acidic solution.

Cr2O72-(aq) + Br-(aq) → Cr3+(aq) + Br2(aq)

A. Cr2O7

2-(aq) + 2 Br-(aq) → 2 Cr3+(aq) + Br2(aq) B. Cr2O7

2-(aq) + 2 Br-(aq) + 14 H+(aq) → 2 Cr3+(aq) + Br2(aq) + 7 H2O(l) C. Cr2O7

2-(aq) + 6 Br-(aq) + 14 H+(aq) → 3 Br2(aq) + 2 Cr3+(aq) + 7 H2O(l) D. Cr2O7

2-(aq) + 6 Br-(aq) + 7 H+(aq) → 2 Cr3+(aq) + 3 Br2(aq) + 7 OH-(aq) 23. Consider the following half-reactions:

Cu2+(aq) + 2 e- → Cu(s) E° = +0.34 V Sn2+(aq) + 2 e- → Sn(s) E° = -0.14 V Fe2+(aq) + 2 e- → Fe(s) E° = -0.44 V Al3+(aq) + 3 e- → Al(s) E° = -1.66 V Mg2+(aq) + 2 e- → Mg(s) E° = -2.37 V

Which of the above metals or metal ions will reduce Fe2+(aq)?

A. Cu(s) and Sn(s) B. Cu2+(aq) and Sn2+(aq) C. Al3+(aq) and Mg2+(aq) D. Al(s) and Mg(s) E. Sn(s) and Al3+(aq)

GAAGCTTC CTTCGAAG


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24. (5 pts) During the process of biological electron transfer, riboflavin can undergo a two electron oxidation-reduction. When riboflavin (Rib) is reduced from its oxidized form (RibO) by the (two electron) oxidation of acetaldehyde (CH3CHO), the balanced reaction is

RibO(aq) + CH3CHO(aq) Rib(aq) + CH3COOH(aq)

The half cell reduction potentials of RibO and acetic acid (CH3COOH) are

RibO(aq) + 2H+(aq) + 2e- Rib(aq) + H2O(l) Eo = -0.21 V

CH3COOH(aq) + 2H+(aq) + 2e- CH3CHO(aq) + H2O(l) Eo = -0.60 V

What is the equilibrium constant for the balanced reaction at 25oC?

A. 2.38 × 1027 B. 1.52 x 1013 C. 3.89 × 106 D. 2.57 x 10-7 E. 6.59 x 10-14

EXTRA CREDIT

25. (4 pts.) Calculate G! o for the reaction below at 125 °C. C2H5OH(g) + 3 O2(g) → 2 CO2(g) + 3 H2O(g)

Species fH!o (kJ/mol) fS

o (J/K·mol) C2H5OH(g) -235.3 282.7

O2(g) 0 205.1

CO2(g) -393.5 213.7

H2O(g) -241.8 188.8

A. -366 kJ B. -1277 kJ C. -1289 kJ D. -1315 kJ E. -3.94 × 104 kJ


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26. (4 pts.) 50 mL of an Arsenic acid (H3AsO4) solution is titrated with 0.1 M NaOH. After 25 mL of the NaOH is added, the resulting solution is ½ the way to first equivalence point.

Ka1 = 2.5x10-4 Ka2 = 5.6x10-8 Ka3 = 3.0x10-13

What is the concentration of AsO4

3- in this solution? A. 2.3 x 10-19 M B. 9.0 × 10-15 M C. 3.0 × 10-13 M D. 7.5 × 10-6 M E. 2.5 × 10-4 M Please sign the following statement at the completion of the exam. I, ________________________________________________(print name) pledge not to discuss this test with anyone who has not it the tests until are graded and returned. _________________________________________________

Documents

Final Exam A - UMass Amherstpeople.umass.edu/ch112sg/Exams/Fall05/F05_Final.pdfChem 112, Fall 05 (Garman/Weis) Name:_____ Final Exam A, 12/20/2005 (P rintC leay)+2points page 1 Before