Chemistry 1A - Fall 2001 - Pines - Final

Chemistry 1A - Fall 2001 - Pines - Final - Chemistry 1A...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chemistry 1A Page 1 of 16 Final Exam (Closed Book, 180 minutes, 350 points) December 12, 2001 Version A Name: TA: SID: Section: Please read this first: Write your name and that of your TA on all 16 pages; On the ScantronTM, bubble in Form A. Test-taking Strategy This test consists of two parts: multiple choice (answers to be circled and entered on the ScantronTM sheet) and short answer. In order to maximize your score on the exam: • • • • Do the questions you know how to do first. Then, go back and spend more time on the questions you find more challenging. Budget your time carefully -- don't spend too much time on one problem. Show all work for which you want credit and don't forget to include units. Page MC 11 12 13 14 15 Total Score Name:_____________________ Page 2 of 16 TA:________________________ Potentially Useful Information ∆G° = ∆H° - T∆S° E = hν λν = c λ deBroglie = h / p = h / mv Ekin (e-) = hν - Φ = hν - hν 0 Z2 E n = − 2 R∞ n ∆H° = Σ ∆H°f (products) - Σ ∆H°f (reactants) ∆S° = Σ S° (products) - Σ S° (reactants) ∆G° = Σ ∆G°f (products) - Σ ∆G°f (reactants) S = kBlnW for aA + bB [C ] c [ D] d Q= [ A] a [ B] b PV = nRT 3 E kin = RT 2 3RT v rms = M cC + dD ∆G° = - RTln K ∆H ° 1 ∆S ° ln K = − + RT R ∆G° = - nF∆Єº ∆E = q + w w = - Pext∆V 3 ∆E = nR∆T 2 pX = - log X pH = pK a + log R = 0.08206 (atm·L) / (mol·K) = 8.314 J/(mol·K) kB = 1.381 x 10-23 J / K h = 6.626 x 10-34 J s 8 c = 3.0 x 10 m.s-1 R∞ = 2.18 x 10-18 J F = 96,485 C / mol 1V=1J/C 1 nm = 10-9 m 1 kJ = 1000 J At equilibrium, Q = K [ A− ] [ HA] Color and Wavelength of Light 800 IR Wavelength (nm) 400 600 200 Red UV Green Blue Average Bond Enthalpies Bond Enthalpy (kJ / mol) C–C 348 C=C 612 838 C≡C C–H 413 H–H 436 Name:_____________________ Page 3 of 16 TA:________________________ Part I Multiple Choice (5 pts each, 225 pts total) Bubble in the correct answer on your ScantronTM form AND circle your answer on the exam. There is only one correct answer for each question, so you should circle and fill in one and only one answer for each question. There is no penalty for an incorrect response. 1) Consider the formation of hydrogen peroxide from the elements in their standard states: H2 + O2 ! H2O2 How does the oxidation number of oxygen change in the above reaction? A) -2 ! -2 B) -1 ! 0 C) 0 ! 0 D) 0 ! -1 E) 0 ! -2 2) Which of the following samples of gas has the highest root mean square speed? A) B) C) D) E) H2 at 200 K He at 200 K Ar at 200 K Ar at 400 K CO2 at 500 K 3) Which of the following reactions exhibits the greatest change in entropy? A) B) C) D) E) CaO (s) + CO2 (g) → CaCO3 (s) N2 (g) + 3 H2 (g) → 2 NH3 (g) C (s) + H2O (g) → H2 (g) + CO (g) CO (g) + H2O (g) → CO2 (g) + H2 (g) 2 NO (g) + O2 (g) → 2 NO2 (g) 4) The empirical formula of a hydrocarbon gas is CH2. If 2.10 g of gas occupies 1.12 L at 1.00 atm and 273 K, what is the molecular formula of the hydrocarbon gas? A) CH B) CH2 C) C2H4 D) C3H6 E) C4H8 Name:_____________________ Page 4 of 16 TA:________________________ 5) Which of the following structural isomers of chlorobromopropane (C3H6BrCl) is chiral (note the H atoms are omitted for clarity)? Cl Cl A) Cl B) C C C Br C) C C D) C Br Br C C C E) none of these C C Br C Cl 6) Which of the following is the mass spectrum of the combustion products of trimethylbenzene (C9H12)? A) B) 18 44 mass C) 18 D) 18 44 mass 44 mass E) 18 44 18 mass 44 mass 7) What is the hybridization of the carbon atoms in ethylene, C2H4? A) sp B) sp2 C) sp3 D) s2p E) s2p4 8) Use the table of average bond enthalpies to estimate ∆H° (in kJ /mol) for the following reaction: C2H4 + H2 → C2H6 A) -290 B) -126 C) 0 D) 126 E) 290 D) PCl3 E) CO2 9) Which of the following molecules has a nonzero dipole moment? A) CH3+ B) BF3 C) AlBr3 Name:_____________________ Page 5 of 16 TA:________________________ 10) A gas expands isothermally against a vacuum (Pext = 0), which of the following is NOT true? A) q = 0 B) w = 0 C) ∆E = 0 D) ∆H = 0 E) ∆S = 0 11) Which of the following is always conserved during a chemical reaction? A) entropy B) molecules C) moles D) mass E) none of these 12) A flask is filled with 16.0 g of methane (CH4) and 16.0 g of oxygen which combust to form carbon dioxide and water. Which is the limiting reagent? A) CH4 B) O2 C) CO2 D) H2O E) none of these 13) To which energy level diagram does the following emission spectrum correspond? ν λ A) B) C) D) E) 14) Light of 121 nm wavelength is emitted in the n =2 ! 1 transition in H. What transition in He+ will emit the same wavelength of light? A) 2 ! 1 B) 2 ! 2 C) 4 ! 1 D) 4 ! 2 E) 4 ! 3 Name:_____________________ Page 6 of 16 TA:________________________ 15) Which of the following has the lowest ionization energy? A)H(1s) B) He(1s4p) C) He(1s3d) D) Li(1s23p) E) Li(1s25s) 16) Which atom or ion can have the electronic configuration [He]2s22p53s1? A) F+ B) F C) Na+ E) Mg+ D) Na 17) Which of the following is required in the least amount to dissolve 10 mg of aluminum hydroxide {Al(OH)3 , Ksp = 1.9 x 10-33} ? A) 8 M NaOH B) 1 M NaOH C) 5 M acetic acid E) H2O D) 1 M acetic acid - 18) Which of the following molecules has a molecular geometry most similar to SF42 ? A) CCl4 B) NH4+ C) BF4 - D) SI4 E) XeF4 19) The Ka for chloroacetic acid (CH2ClCOOH) is 5.65 x 10-3. If the equilibrium concentrations of [CH2ClCOOH] = 8.88 x 10-2 M and [CH2ClCOO-] = 2.24 x 10-2 M, what is the corresponding [H3O+] (in M)? - CH2ClCOOH (aq) + H2O (l) ↔ CH2ClCOO (aq) + H3O+ (aq) A) 5.65 x 10-3 B) 8.88 x 10-2 C) 2.24 x 10-2 D) 5.01 x 10-4 E) 6.36 x 10-2 Name:_____________________ Page 7 of 16 TA:________________________ 20) Formic acid is a weak acid with pKa = 3.75. How many mL of 0.10 M NaOH solution should be added to 100.0 mL of 0.10 M formic acid solution to make a buffer solution with pH = 3.27? A) 0.0 B) 25.0 C) 50.0 D) 75.0 E) 100.0 21) The ionization energy of a certain one-electron species in its ground state is 3.28 x 104 kJ / mol. How many protons are contained in its nucleus? A) 1 B) 2 C) 3 D) 4 E) 5 D) F- E) O2- 22) Consider the conversion of ozone to oxygen: 2 O3 ! 3 O2 ∆H° = -286 kJ / mol Which of the following is true about the bond enthalpies (E)? A) EO=O > 2 EO-O B) EO=O = 2 EO-O C) EO=O < 2 EO-O D) EO=O < EO-O E) EO=O = EO-O 23) Which of the following atoms or ions has the smallest radius? B) Na+ A) Mg C) Ne 24) When a system has reached equilibrium, which of the following is true for the rates of the forward and reverse reactions? A) B) C) D) E) Forward = 0 Reverse = 0 Forward < Reverse Forward = Reverse Forward > Reverse Name:_____________________ Page 8 of 16 TA:________________________ 25) Why is the ionization energy for Na+ larger than the ionization energy for Ne? A) B) C) D) E) Neon is a noble gas. Neon has a smaller radius that Na+. Neon has fewer protons. The outer electrons in sodium are in a higher energy level. Sodium is more metallic. 26) Consider the following reaction at equilibrium: 2 NH3 (g) → N2 (g) + 3 H2 (g) ∆Hû = +92.4 kJ Removing some N2 (g) from the system at equilibrium will __________. A) B) C) D) E) increase the partial pressure of NH3 (g) at equilibrium decrease the partial pressure of H2 (g) at equilibrium increase the value of the equilibrium constant cause the reaction to shift to the right increase the reaction temperature 27) Of the following, ∆Gfû is not zero for __________. A) B) C) D) E) O2 (liquid) C(graphite) N2(gas) F2(gas) Cl2(gas) 28) What is the pH of a 0.10 M HCl solution? A) 0.00 B) 1.00 C) 1.89 D) 3.75 29) What is the change in the internal energy, ∆E (in J) of a system that absorbs 4000 J of heat and that does 2000 J of work on the surroundings? A) B) C) D) E) 6000 4000 2000 -2000 -4000 E) 10.00 Name:_____________________ Page 9 of 16 TA:________________________ 30) At lower temperatures A) B) C) D) E) Chemical reactions are more favorable. Chemical reactions are less favorable. Equilibrium constants are smaller. Equilibrium constants are larger. Chemical reactions are sometimes more favorable. 31) We have seen many times in lecture that heat is given off in the combustion of hydrogen gas. Which of the following is responsible for the heat? A) B) C) D) E) Breaking H-H and O-O bonds. Breaking O-H bonds. Forming H-H bonds and O-O bonds. Forming O-H bonds. Vaporization of the water formed. 32) For the reaction : A(l) + D(g) → X(g) + Z(s) having ∆Gû = -500 kJ / mol at 25ûC, the equilibrium mixture __________. A) B) C) D) E) will consist almost exclusively of A and D. will consist almost exclusively of X and Z. will consist almost exclusively of A and Z. will consist of significant amounts of A, D, X, and Z. has a composition predictable only if one knows T and ∆Hû. 33) A beam of yellow light does not eject electrons from a certain metal. What change to the beam should be made in an attempt to eject electrons? A) B) C) D) E) Increase the wavelength. Increase the intensity. Increase the frequency. Change the color to red. None of the above will work Name:_____________________ Page 10 of 16 TA:________________________ 34) A 0.10 mole sample of He (g) is added to a 1.00 L flask containing Ar gas at 1.00 atm at 273 K. What is the partial pressure of He? A) 0.10 atm B) 1.24 atm C) 1.00 atm D) 2.24 atm E) 3.24 atm 35) A 0.10 mole sample of He (g) is added to a 1.00 L flask containing Ar gas at 1.00 atm at 273 K. What is the total pressure in the flask? A) 0.10 atm B) 1.24 atm C) 1.00 atm D) 2.24 atm E) 3.24 atm Use the following table to answer questions 36-38. Reaction Standard Reduction Potential (Volts) Ag+1 (aq) + e- → Ag (s) +0.80 Cu+2 (aq) + 2 e- → Cu (s) +0.34 Ni+2 (aq) + 2 e- → Ni (s) -0.23 Fe+2 (aq) + 2 e- → Fe (s) -0.41 Zn+2 (aq) + 2 e- → Zn (s) -0.76 36) What will be produced when an iron rod is placed in a solution of AgNO3 solution? A) H2 (g) B) Ag (s) C) Fe+2 D) AgNO3 (s) E) B and C D) 0.80 E) 1.14 D) 78 E) 147 37) What is the potential (in volts) for the cell described below? Cu | CuSO4 (1.0 M) || AgNO3 (1.0 M) | Ag A) 0.16 B) 0.34 C) 0.46 38) What is the ∆Gû (in kJ) for the cell described below? Zn | ZnSO4 (1.0 M) || H2SO4 (1.0 M) | H2 | Pt A) -147 B) -78 C) 0 Name:_____________________ Page 11 of 16 TA:________________________ For Questions 39-45, which sketch best depicts the dependence of Y vs X for the following: A) Y B) Y C) Y X D) Y X E) Y X X X 39) P vs V for an ideal gas. A) A B) B C) C D) D E) E C) C D) D E) E 40) ∆G° vs T for the reaction Cl2 → 2 Cl . A) A B) B 41) ln K vs 1/T for dissolution of borax Na2[B4O5(OH)4]•8H2O (the reaction is endothermic). A) A B) B C) C D) D E) E C) C D) D E) E D) D E) E 42) Kinetic Energy vs T for 1 mole of an ideal gas. A) A B) B 43) Absorbance vs. concentration for a dilute solution of sunscreen. A) A B) B C) C 44) ∆Єº vs number of moles of magnesium for the reduction of magnesium metal. A) A B) B C) C D) D E) E C) C D) D E) E 45) Photon energy versus wavelength of light. A) A B) B Name:_____________________ Page 12 of 16 TA:________________________ Part 2: Short Answer Problems (125 pts total) Instructions: Enter answers in the boxes where provided. Show all work for which you wish to receive credit. Where explanations are required, only the first fifteen words will be considered for your grade. 1.) (85 pts) Nitrous acid (HNO2) has a pKa = 3.34. HNO2 (aq) + H2O (l) - NO2 (aq) + H3O+ (aq) a) (15 pts) Calculate ∆G° (in kJ / mol) for the reaction of nitrous acid with water at 25 °C. pKa = - log Ka 10-3.34 = Ka Ka = 4.57 x 10-4 ∆G° = -RTlnK = −8.314 J • 298 K ln(4.57 × 10 −4 ) mol • K ∆G°: 19.1 kJ / mol = 19.1 kJ / mol b) (10 pts) Classify HNO2 as an acid or base by circling an option below. Provide an explanation. strong acid strong base weak acid Explanation: Proton donor, ∆G° > 0, equilibrium lies to the left weak base none of these Name:_____________________ Page 13 of 16 TA:________________________ c) (10 pts) Which of the following pH ranges corresponds to the region where a solution containing HNO2 is an effective buffer. Circle your answer and provide an explanation. 4.34 – 2.34 5.34 – 1.34 5.34 – 7.34 Explanation: Buffer region is around pKa ± 1 pH unit d) (25 pts) A solution 100 mL 0.1 M HNO2 is titrated to the equivalence point with 0.1 M NaOH. i) What is the total volume of the solution(in mL)? 0.1 L (0.1 M HNO2) = 0.01 moles HNO2 0.1 moles NaOH = 0.1M NaOH X L X = 0.1 L Vtot = 0.2 L = 200 mL V: 200 mL ii) What is the pH of the solution? at the equivalence point 0.01 moles NaNO2 have been formed [NaNO2] = 0.01 moles / 0.2 L = 0.05 M Kb = Kw / Ka = 1 x 10-14 / 4.57 x 10-4 = 2.18 x 10-11 NaNO2- (aq) + H2O (l) Kb = HNO2 (aq) + OH- (aq) pH: 8.0 [ HNO2 ][OH − ] x2 = = 2.18 × 10−11 if x << 0.05 x = 1.04 x 10-6 = [OH-] − NaNO2 0.05 − x pOH = -log (1.04 x 10-6) = 5.98 pH = 14 – pOH = 8.0 iii) For the titration of HNO2, the pH at the equivalence point is not 7. Explain. Explanation: HNO2 is a weak acid, the titration generates a conjugate base ! pH > 7 Name:_____________________ Page 14 of 16 TA:________________________ - e) (25 pts) Draw a pair of valid resonance lewis dot structures for the NO2 ion. N N O O O O - i) Which of the following best describes the bond angle in NO2 . Circle your answer. = 180° = 120° >120° <120° the repulsion from the lone pair of electrons will create a bond angle less than the ideal 120 - ii) What is the nitrogen/oxygen bond order NO2 ? Bond order = total # of N / O bonds total # of resonance structures Bond order: 1.5 - iii) Does NO2 have a dipole moment? Circle your answer. Yes No - unequal distribution of electrons about the central atom make NO2 polar Name:_____________________ Page 15 of 16 TA:________________________ 2.) (40 pts) Consider the dissociation of molecular chlorine (Cl2) to atomic chlorine (Cl): Cl2 → 2 Cl a) (15 pts) The bond enthalpy of the Cl-Cl bond is 242 kJ / mol. What is the maximum wavelength (λ, in nm) of light required to break the bond? For 1 mole of bonds: E = hν(6.02 x 1023) = 242 kJ / mol For a single photon to break a single bond: J 242000 mol = 4.01 × 10-19 J = hν = h c E= bonds λ 6.02 × 1023 mole λ = 495 nm b) (10 pts) The minimum frequency of light required to ionize a Cl atom corresponds to the UV region in the electromagnetic spectrum. On the axes provided, sketch a plot of the kinetic energy of electrons ionized from a Cl atom as a function of light frequency. Ekin IR Red Green Blue UV ν Name:_____________________ Page 16 of 16 TA:________________________ c) (8 pts) Using ↑ and ↓, fill in the corresponding electronic orbital diagrams for Cl2 and Cl. Cl2: ↑↓ 3pπ* ↑↓ 3pπ 3pσ* Cl: ↑↓ ↑↓ 3pπ* ↑↓ ↑↓ ↑↓ 3pπ 3pσ ↑↓ ↑ 3p 3s ↑↓ 3sσ* ↑↓ 3sσ d) (7 pts) What is the change in paramagnetism for the Cl2 dissociation reaction. Circle your answer. Increases Decreases Stays the same ...
View Full Document

This note was uploaded on 08/31/2009 for the course CHEM 1A taught by Professor Nitsche during the Fall '08 term at University of California, Berkeley.

Ask a homework question - tutors are online