chem1A-Fall01-mt1-unknown-soln

chem1A-Fall01-mt1-unknown-soln - Chemistry 1A Page 1 of 10...

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Unformatted text preview: Chemistry 1A Page 1 of 10. Midterm Exam 1 September 20, 2001 (Closed Book, 90 minutes, 150 points) Version D Name: TA: SID: Section: ______ Identification Sticker Test-taking strategy: PLEASE READ THIS FIRST! Write your name and that of your TA on all 10 pages. 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. Potentially Useful Information: E = hν, λν = c λ deBroglie = h / p = h / mv Ekin (e-) = hν - Φ = hν - hν 0 h = 6.626 x 10-34 J s c = 3.0 x 108 m.s-1 1 nm = 10-9 m Page Multiple Choice 7 8 9 10 Total: Color and Wavelength of Light Wavelength (nm) 400 600 800 IR Red Green Blue Points 200 UV Name:_____________________ page 2 of 10 TA:______________________________ Part I Multiple Choice (4 pts each, 72 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.) The answer to question 1 is D. Bubble in D on your ScantronTM form A) A B) B C) C D) D E) E D) wine E) hydroxide 2.) Which of the following is an element? A) air B) water C) uranium 3.) When 686.0 g of the lead oxide Pb3O4 is heated, decomposition occurs producing 16.0 g of O2 gas and 670.0 g of a different lead oxide. What is the empirical formula of this second oxide? A) PbO B) Pb2O C) PbO2 D) Pb2O3 E) Pb1.5O 4.) Which of the following molecules has an electric dipole moment? A) CH4 B) BF3 C) XeF2 D) ClF3 E) CO2 Name:_____________________ page 3 of 10 TA:______________________________ 5.) How many structural isomers exist for the chlorinated hydrocarbon chlorobutane, C4H9Cl? A) 2 B) 4 C) 6 D) 8 E) 10 6.) Which of the following is a valid Lewis Dot Structure for hydrazine, N2H2? A) H = N = N = H D) H − N ≡ N − H •• •• •• •• • B) H − N − N − H •• • C) H − N = N − H •• E) H − N = N − H 7.) Which of the following molecules or ions is NOT linear? A) ICl2 - B) CO2 C) SO2 D) C2H2 E) HCN Name:_____________________ page 4 of 10 TA:______________________________ 8.) Which of the following isomers of the hydrocarbon heptane, C7H16, is chiral (the hydrogen atoms are omitted from the structures)? A) C C C C C C C B) C C C C C C C C C) C C C D) C C C C C C C C E) None of the above C C 9.) Which of the following molecules or ions is isoelectronic with CN-? A) O2 B) N2 C) NO D) NO- E) CN+ 10.)Which compound has the highest percentage of iodine by mass? A) IF3 B) BaI2 C) FeI3 D) AlI3 E) CaI2 11.)Cupric sulfate solution is blue. Through a blue colored lens, what color will a cupric sulfate solution appear? A) white B) black C) blue D) red E) green 12.)Which atom has the greatest number of neutrons? A) 27Al B) 28Si C) 32S D) 32P E) 35Cl Name:_____________________ page 5 of 10 TA:______________________________ 13.)One mole of carbon atoms reacts to form C60, buckminsterfullerene molecules. How many molecules of C60 are formed? A) 0 C) 1.0 x 1022 D) 6.0 x 1023 E) 3.6 x 1025 B) 1 14.)Atoms of 32S traveling at 2.00 x 103 m/s have a deBroglie wavelength of 6.23 x 10-12 m. Which atoms, traveling at 2.00 x 103 m/s have a deBroglie wavelength of 1.24 x 10-11 m? A) 16O B) 64Cu C) 12C D) 8Li E) 48Ti 15.)Which energy level diagram corresponds to the observed spectrum shown? λ ν A) B) C) D) E) none of the above Name:_____________________ page 6 of 10 TA:______________________________ 16.)A photon of blue light (400 nm) is absorbed and 2 photons are emitted as illustrated in the energy diagram below. To which color light do the two equivalent emitted photons correspond? 400 nm A) IR ? 3 2 1 B) Red ? C) Green D) Blue E) UV 17.)In which of the molecules or ions below does nitrogen (N) have the highest oxidation state? A) CN- C) NO3- B) NO2 D) NH3 E) N2 18.)The combustion products of a hydrocarbon with which empirical formula yield the following mass spectrum? 18 44 mass A) C4H B) C2H C) CH D) CH2 E) CH4 Name:_____________________ page 7 of 10 TA:______________________________ Part 2: Short Answer Problems (78 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.) (39pts) Acrylonitrile is an important building block for synthetic fiber. It can be made by the reaction of propane with ammonia and oxygen, as follows: 2C3H6 (g) + 2NH3 (g) + 3O2 (g) → 2C3H3N (l) + 6H2O (l) a) (11 pts) What mass of Acrylonitrile is formed by the reaction of 1.0 mole of propane and 2.0 moles of ammonia (NH3) in the presence of excess oxygen. Propane (C3H6 ) is the limiting reagent. (1 mol C3H6 ) (2 mol C3H3N)/(2 mol C3H6) = 1 mol C3H3N MW(C3H3N) = 53 g/mol Mass Acrylonitrile: 53 g b) (6 pts) Acrylonitrile can be formed in the presence of ozone, O3 , rather than molecular oxygen, O2. Balance the chemical equation for this reaction. 1 C3H6 (g) +1 NH3 (g) + 1 O3 (g) → 1 C3H3N (l) + 3 H2O (l) Name:_____________________ page 8 of 10 TA:______________________________ c) (11 pts) Draw a valid resonance pair of Lewis Dot Structures for Ozone. O O O O O O d) (11 pts) What is the bond order of the oxygen-oxygen bond in i) oxygen (O2) and ii) Ozone (O3). Explain your answer. i) oxygen (O2) Bond order 2 Explanation: To obtain octets, on both “O” atoms, a double bond is needed (no resonance possible). ii) ozone (O3) Bond order 1.5 Explanation: Bond order = (total # bonds between the O atoms) / (# resonance structures) 2.) (39 pts) Sodium metal, Na has a work function equal to 4.3 x 10-19 joules. Name:_____________________ page 9 of 10 TA:______________________________ a) (10 pts) Calculate the lowest frequency and the corresponding wavelength of light sufficient to eject a photoelectron from sodium metal? Ekin = hν - Φ 0 = hν - 4.3 x 10 Frequency 6.5 x 1014 Hz -19 ν = 6.5 x 1014 Hz c = λν (3 x 108 m/s)/ 6.5 x 1014 Hz = 460 nm Wavelength 460 nm b) (8 pts) Will red light eject an electron from sodium metal? Circle your answer and explain. Circle one: YES NO DEPENDS Explanation: The frequency of red light is too low to overcome the work function Name:_____________________ page 10 of 10 TA:______________________________ c) (10 pts) How many photoelectrons are ejected from sodium metal by light of wavelength λ = 400 nm (1 nm = 10-9 m) that delivers a total energy of 2.23 x 10-18 J? Ephoton = hc/λ Ephoton = 4.97 x 10-19 J Etotal = n x 4.97 x 10-19 J n = number of photons # of photoelectrons 2.23 x 10-18 J / 4.97 x 10-19 J = 4.49 d) (11 pts) On the graph below, plot the kinetic energy of electrons ejected from sodium metal as a function of light frequency and explain. Ekin ν IR Red Green Blue UV Explanation: Linear relationship of photoelectric effect and the work function is in the blue ...
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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 Berkeley.

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