chem1a-Spring96-final-Chandler -exam

chem1a-Spring96-final-Chandler -exam - Name:...

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Unformatted text preview: Name: _______________________ Section 1: Multiple Choice. 20 questions, 6 points each. Page 2 of 14. Instructions: For the following questions, circle the answer on the exam sheet and bubble in the correct answer on your Scantron sheet. Unless you are specifically told that there might be more than one answer to a problem, assume that only one answer is correct. No credit will be awarded for partially-correct answers. 1.) You are taking test version A. Please fill in bubble "A" on your Scantron sheet. 2.) Which of the following compounds exhibit a dipole moment? Mark all that apply. A) CO2 B ) CO C) SF6 D) CH4 E) N2 3.) At 300 K, argon atoms travel with an rms speed of 433 m•s-1. Which of the following gases has one-half the rms speed of argon at 300 K? A) O2 B) C6H8 C) N2 D) Br2 E) Ne 4.) 1.0 mole of sodium hydrosulfide, NaHS, (HS- is the conjugate base of the weak acid H2S, whose pKa is 6.9) is dissolved in 1.0 L of water. HCl is then added until the pH is 6.4. Which of the following has the highest concentration? A) H3O+ B) OH- C) H2S D) H2 E) HS- 5.) Which of the following species will oxidize Co, but not Br- under standard conditions? A) Cl2(g) B) Ag(s) C) Pb2+ D) Li+ E) None of these. 6.) How many moles of Na2SO4 can be added to 1.0 L of an aqueous 0.10 M Ca(NO3)2 solution before a precipitate forms? Assume that Na2SO4 and Ca(NO3)2 dissociate completely in water. The Ksp for CaSO4 is 2.4x10-5. A) 2.4x10-6 B) 2.4x10-5 C) 2.4x10-4 D) 4.8x10-4 E) 4.9x10-3 7.) Which of the following can have the electron configuration 1s22s22p63s23p64s23d104p4? A) Ga3+ B) Te C) As- D) Br E) None of these. 8.) Which of the following has the highest ionization energy? A) F B) F- C) Ne D) Na E) Na+ 9.) How many atoms are there in 36 g of pure water? A) 3.0x1025 B) 3.6x1024 C) 1.8x1024 D) 1.2x1024 E) 6.0x1023 Name: _______________________ Page 3 of 14. 10-13. In the next four problems, choose which of the following five graphs best describes the behaviors listed below. A) B) C) D) E) 10.) [H3O+] as a function of NaOH(s) added to water. 11.) PV as a function of P for an ideal gas at 25 °C. 12.) The de Broglie wavelength, λ, as a function of speed for a sodium atom. 13.) lnK as a function of 1/T for an endothermic reaction. 14.) The work function, Φ, for chromium is 7.2x10-19 J. A photon of which energy (hν) will eject an electron with the lowest electron kinetic energy? A) 2.0x10-19 J B) 5.3x10-19 J D) 2.7x10-18 J C) 1.3x10-18 J E) 6.6x10-18 J 15.) A compound comprised of only oxygen and carbon is found to contain 27.29% carbon by mass. What is the empirical formula for the compound? A) CO 16.) λ A) B) CO2 C) C2O3 D) C2O2 E) C27O73 Which of the following energy level diagrams could give rise to the emission spectrum pictured to the left? B) C) D) E) Name: _______________________ Page 4 of 14. 17.) Using bond enthalpies, estimate ∆H° for the following reaction (in kJ•mol-1). H C C H H A) -550 H C C H H H H H + H H H B) -350 C) -100 D) 350 E) 550 18.) A gaseous mixture of NO2(g) and N2O4(g) is in equilibrium: 2 NO2(g) N2O4(g) If the volume is suddenly doubled without changing the temperature, which of the following will be true once the system regains equilibrium (compared to the original system before the volume was changed)? A) The total pressure will be higher. B) The partial pressure of N2O4(g) will be higher. C) The mole fraction of NO2(g) will be higher. D) The equilibrium constant, K, will be lower. E) The equilibrium constant, K, will be higher. 19.) Which of the following reactions/processes has a negative ∆S°? A) B) C) D) E) LiCl(s) -----> Li+(aq) + Cl-(aq) H2O(λ) -----> H2O(g) 2 MgO(s) + C(s) -----> CO2(g) + 2 Mg(s) BF2Cl(g) + BCl2F(g) -----> BCl3(g) + BF3(g) PCl5(g) -----> PCl3(g) + Cl2(g) 20.) A 50 g iron block (specific heat = 0.449 J•g-1•K-1) is heated to 100 °C and placed in a calorimeter containing 50 mL of water (specific heat = 4.18 J•g-1•K-1) initially at 0 °C. After several minutes, the final temperature of the water will be approximately: A) B) C) D) E) Below 0 °C. Between 0 °C and 40 °C. Around 50 °C. Between 60 °C and 100 °C. Above 100 °C. Name: _______________________ Page 5 of 14. Section 2: What's Wrong. 8 questions, 10 points each. For this section, in no more than twenty words per response, explain what is wrong with the following pictures. Note: only the first 20 words of each answer will be read! 1.) For the plating of silver onto a gold plate: Before Au Au Au Ag+ Cl- Answer: After Ag Au3+ Cl- 2.) For two ideal gases at 25 °C: Answer: CO2 probability CH4 speed Z2 3.) Energy level diagrams for the one electron species H and He+, where E n = − 2 R y : n H n=4 n=3 n=2 He+ n=5 n=4 n=3 Answer: E n=1 n=2 4.) For the diffraction of light through a slit: hν Detector Answer: Name: _______________________ Page 6 of 14. 5.) An energy level diagram for absorption and emission: λ = 1000 nm λ = 400 nm E Answer: λ = 600 nm 6.) For the addition of 0.1 M HCl to a solution in which initially [HA] = [A-]: Answer: pH 0 0 moles of H O+ added 3 7.) For the vapor pressure of water: Pvap Answer: (atm) 1 T (°C) 25 8.) An ion exchange column with Ca2+ ions exchanging with OH- ions: Ca2+ Ion Exchange Resin OH- Answer: Name: _______________________ Page 7 of 14. Section 3: Short Answer. 10 questions, 20 points each. Answer the following ten short answer questions. Partial credit will be given, so show your work whenever possible. Your final answers must be written in the boxes provided. 1.) Consider an ideal gas at a volume of 1 L and a pressure of 1 atm. The gas is expanded adiabatically and irreversibly against a constant external pressure of 0.1 atm until it reaches a volume of 2 L. For each quantity below, indicate (by checking the box) whether it is =0, >0, or <0 for the overall adiabatic and irreversible expansion. Quantity ∆Psys ∆Vsys ∆Tsys w q ∆Esys ∆Esurr ∆Ssys ∆Ssurr ∆Stot =0 >0 <0 2a.) Using the table on page 14, calculate ∆H° and ∆S° for the following reaction: CO(g) + 2 H2(g) CH3OH(g) ∆H°= ∆S°= b.) Is this reaction spontaneous under standard conditions at 25 °C? Circle your answer. Yes c.) No Assuming ∆H° and ∆S° are independent of temperature, at which temperature will this reaction be at equilibrium? Assume all the pressures are 1.0 atm. Answer: Page 8 of 14. Name: _______________________ 3a.) Formic acid (HCOOH) has a Ka=1.8x10-4, pKa=3.74. If 0.050 moles of formic acid are dissolved in 1.0 L of water, what will the pH be? pH= b.) How many mL of 0.10 M NaOH should be added to the solution in a) in order to raise the pH to 3.74? Answer: c.) The solution in a) is titrated to the equivalence point with 500 mL of 0.10 M NaOH. This solution now has the same pH as which of the following. Circle your answer. 0.10 moles of HCOO-Na+ (sodium formate) in 3.0 L of water. 1.0x10-5 moles of NaOH in 1.0 L of water. 0.050 moles of formic acid and 0.10 moles of NaOH in 1.5 L of water. Page 9 of 14. Name: _______________________ 4a.) Draw the Lewis electron dot structure for XeF4. Include all the lone pairs. Lewis Dot Structure: b.) Which of the following best describes the geometry of the electron pairs (including bonds) around the central atom? Circle your answer. Linear Trigonal Planar Tetrahedral Trigonal Bipyramidal Octahedral c.) Name, describe, or draw the molecular geometry of the molecule. Molecular Structure: Name: _______________________ Page 10 of 14. 5a.) Balance the following combustion equation: ______ C3H8(g) + ______ O2(g) --------> ______ CO2(g) + ______ H2O(g) b.) 1.0 atm of C3H8(g) and 4.0 atm of O2(g) are sealed in a flask and ignited. How many moles of O2(g) remain once the reaction has gone to completion? Assume all the gases are ideal. Answer: c.) After the above reaction has run to completion, what is the total pressure in the flask? Answer: 6.) An excited state of helium is created such that one electron is in the 1s orbital and one electron is in a 3p orbital. a.) What is the ionization energy of the 3p electron in He(1s3p)? IE= b.) The first ionization energy for He(1s2) is found to be 2372 kJ•mol-1 (which is 1.8Ry). What is the effective charge, Zeff, for the ionization of a 1s electron? Zeff= c.) Which one of the following is a possible excited state electronic configuration for lithium? Circle your answer. 1s2 1s21p1 1s3 1s22s1 1s23p1 Page 11 of 14. Name: _______________________ 7a.) Write a balanced spontaneous net reaction in acidic solution based on the unbalanced and incomplete half-reactions below. MnO4- + 5e- --------> Mn2+ O2(g) + 4e- --------> 2 H2O Answer: b.) Under standard conditions, what is ∆ε° for this reaction? ∆ε°= c.) What would happen to ∆ε if you lowered the pH of the solution? Limit yourself to 20 words or less. Answer: Name: _______________________ Page 12 of 14. 8.) The graph pictured below is an isotherm for Br2 at 25 °C. P(atm) 1 A D B 0 E C V For the following four questions, circle the point (or points) on the isotherm (A-E) which describes the statement given. Circle all that apply. a.) Only gas is present. A B C D E b.) Only liquid is present. A B C D E c.) Gas and liquid are in equilibrium. A B C D E d.) Point with the lowest compressibility. A B C D E e.) What is the vapor pressure of Br2(λ) at 25 °C? Pvap= 9.) At 25 °C, the equilibrium constant for the following reaction is 4.2x10-31. N2(g) + O2(g) 2 NO(g) Kp = a.) Write the equilibrium expression for this reaction. b.) NO(g) is placed in a vacuum at 25 °C and dissociates until it reaches its equilibrium partial pressure of 1.0x10-16 atm. What is the partial pressure of N2(g) at equilibrium? PN2= c.) If 1.0 atm of N2(g) is mixed with 1.0 atm of O2(g) at 25 °C, what will be the equilibrium partial pressure of NO(g) in equilibrium? PNO= Page 13 of 14. Name: _______________________ 10.) A student is doing an experiment to determine the amount of beta-carotene (a plant pigment) in a leaf using a UV-VIS spectrometer. First she obtains some pure beta-carotene and makes several dilutions using distilled water to obtain five standard solutions with known concentrations. Next the student determines that the absorption maximum for beta-carotene is at 455 nm. She then blanks the spectrometer using pure distilled water, and measures the absorbance of her five standard solutions at 455 nm, obtaining the following results: Absorbance 0.000 0.120 0.243 0.364 0.484 0.605 1 Calibration Curve 0.8 Absorbance Concentration 0.0000 M (blank) 0.0010 M 0.0020 M 0.0030 M 0.0040 M 0.0050 M 0.6 0.4 0.2 0 -0.2 -2 0 2 4 6 8 Concentration (mM) 10 Next she extracts all the pigments from 0.25 g of a leaf using 95% ethanol, some CaCO3, and sea sand; grinding the leaf with a mortar and pestle. She then filters all of the green solution into a 100 mL volumetric flask, rinsing the filtrate with 95% ethanol until it is colorless, and brings the total volume to 100 mL using 95% ethanol. Then, using the spectrometer, the student determines the absorbance to be 0.918 at 544 nm. Using the equation of the regression line from her calibration curve, she determines the concentration of her solution to be 0.0076 M. This corresponds to 163% of the mass of the leaf being beta-carotene! There are at least 4 mistakes that the student made in this experiment. Find 3 of them. Hint: she did not make any math errors. Limit you answers to 20 words or less. Mistake #1: Mistake #2: Mistake #3: Name: _______________________ Page 14 of 14. Standard Reduction Potentials Half Reaction ε° (V) Half Reaction ε° (V) MnO4- + 8 H3O+ + 5e- -----> Mn2+ + 12 H2O Au3+ + 3e- -----> Au(s) 1.49 Ag+ + e- -----> Ag(s) 0.80 1.42 0.00 Cl2(g) + 2e- -----> 2 ClO2(g) + 4 H3O+ + 4e- -----> 6H2O 1.36 2 H3O+ + 2e- -----> H2(g) + H2O Pb2+ + 2e- -----> Pb(s) Br2(λ) + 2e- -----> 2 Br- 1.07 1.23 Co2+ + 2e- -----> Co(s) Li+ + e- -----> Li(s) Bond Enthalpies Bond ∆H° (kJ • mol-1) Bond ∆H° (kJ • mol-1) C-H C-C 400 350 C=C H-H 600 450 Standard Thermodynamic Properties Substance ∆H° (kJ • mol-1) S° (J • mol-1 • K-1) ∆G° (kJ • mol-1) Br2(g) 31 245 3.14 Br(λ) 0 152 0 CO(g) -110 198 -137 CH3OH(g) -200 240 -162 H2(g) 0 130 0 H(g) 225 115 203 Possibly Useful Information Absolute T(K) = T(°C) + 273.15 ∆E = q + w N0 = 6.022x1023 w = -Pext∆V PV = nRT ∆Etot = ∆Esys + ∆Esurr R = 0.0821 L • atm • mol-1 • K-1 ∆Stot = ∆Ssys + ∆Ssurr R = 8.31 J • mol-1 • K-1 ∆G = ∆H - T∆S 3RT M ∆G° = -RTlnK u rms = [HA] − [A ] Kw=[H3O+][OH-] pH = pKa − log V ∆ Ssys = nRln 2 V1 q rev ∆ Ssurr = − T ∆ H° 1 ∆ S° + R T R hc E = hν = λ h mu = p = λ 2 Z E n = − 2 R y , Ry=1312 kJ•mol-1 n 1 2 1 ∆ E = −Z 2 − 2 R y nf ni 2 Z IE = eff Ry n2 mu2 E kinetic = 2 ln K = − Eelectron = Ephoton - Φ -0.13 -0.28 -3.05 ...
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This note was uploaded on 03/30/2010 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at University of California, Berkeley.

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