Chem_2009FALL_Exam 2 Key

Chem_2009FALL_Exam 2 Key - Name TA Section Chemistry 109...

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Unformatted text preview: Name / TA Section Chemistry 109 Professors Keutsch and Mahanthappa Fall 2009 Exam 2 Instructions: 1. This exam contains 11 pages of questions, a single sided page with formulas, a page with constants and DNA nucleotide structures, a table of amino acids, and a periodic table. If a page is missing, take the exam to the proctor immediately. 2. Print your name on all pages. 3. Show all of your work for maximum partial credit. Honor code: By the definition of academic integrity, this exam is solely my own work. ' ' You do not need to answer all'of the questions. ' CIRCLE only the questions that you want graded. I Part A (Circle 2) 1 F Part B (Circle 3) Part C (Circle 1) TOTAL Name Part A. Basic Questions. Answer TWO of the following three questions. On the first page of the exam circle which two questions you want graded. l. (15 pts. total, 3 pts. each) Circle the species with the indicated property among the choices below. a) (3 points) Can donate the most hydrogen bonds: CH4 HF b) (3 points) Largest dipole moment: c) (3 points) Largest London forces: H2 N2 d) (3 points) Strongest intermolecular forces: C2H6 C4Hlo e) (3 points) Highest boiling point: methanol —— OH V . . .l, ,gmmawww " ' swim" ‘ n-butanol I /\/\ H : lfilafillfii‘l'uzgkmfx Y;..€:‘Jl1‘r:"ot’if"§fl'Efiiirtiuf‘i'flfifl} 2,2—dimethyl-2— propanol OH Name 2. (15 pts. total, 5 pts. each) For each of the three compounds below: - draw a Lewis Diagram — draw the electron pair geometry and label the angles - name the molecular shape _ Remember to Show all [one pairs. Draw the geometry at the . . central atom, including lone Name of the molecular Lew1s D1agram electron pairs w/angles , Shape labeled BCCIZ SF4 XCO3F2 Name 3. (15 pts. total, 3 pts. each) \\ . T C\ /C§ "/H N\\\ 1 H t f C\ / l H H O H/C\C/C\C/// 3 \. V \H I / I H H ., \H 170 J, Wattage} / a) Fill in the missing lone pairs to obey the octet rule. b) Clearly identify one sigma bond with a G and a pi-bond with a 7t. 0) Draw a resonance structure of the structure above so there are two total. Include the formal charges of the resonance structures where appropriate. d) What is the hybridization of the atoms marked 1, 2, 3? What are the ideal angles of the arrangement of electron densities around the atoms ignoring distortions? s? (.80 ° 2 gpl ma ° LE3: m '0' c) How does the length of the C-C bond in the ring compare to a C-C single bond and a C=C double bond? Explain briefly. Fat-Wt éflflwgém w fl: ’Wta W fa [a 4/ a (“"6 Wfié /. w w . At /«M”fi‘"flm‘é Hilary-r“ Jr) //éi“ Ann MW fitmb'fl'wgfi‘m 6’ M a gala “ Name Part B. Competency Questions. Answer THREE of the following four questions. On the first page of the exam circle which three questions you want graded. 4. (17 pts. total) This question is related to the reactivity and properties of the three isomers of C4HgO shown below. 0 A C a) (5 points) Which of these substances has the highest boiling point? Explain your answer using terminlo of intermolecular forces. C M] a alflhmfmr/ éittwmlgmagwa"newémnaeféw firrwtee , M 77" fig“) b) (4 points) Draw the products, if any, of reacting the above molecules with an excess of KzCr207 and state whether their boiling points will be higher or lower than those of reactants. A —’ 7% mm. "B C M law My d) (4 points) The butanoic acid shown below is the oxidation product of a different isomer of C4HgO with excess K2Cr207, Identify the precursor compound C4H80. O Precursor e) (4 points) Explain why butanoic acid is acidic using resonance structures. W . ' ,l A l Viz/4?? “mew-it“ M‘ \ m M» 1,. ‘ ‘ 55:“ ,r _ a, , y rewwfiw “"4 /W»“W Wm” M“- zéw (9 «W {fa ’3 e) E ’0 MOM. “a )“i + 4' M\ C) Name 5. (17 pts. total) Refer to the follow data regarding the rate of a reaction 2A + B —> C + D at a fixed temperature. Initial Concentrations 1 Initial Rate (M s") [A]— _[B]_ Ex eriment no. 0.10 2.5 x 10'7 0.40 v 5.0 x107 1 0.40 2.0 x 10"6 0.080 y 0.20 2.8 x 10‘6 a. (5 pts.) Determine the order of this reaction with respect to [A]. Explain your reasoning briefly. The 2rd m4. CW L W 0421 __ Aim]? £871? a W ‘t W “‘3 — ktmteil’; W (OOZY‘C—L) “‘9 y” z 2' 3 / 3 010+ 2- b. (5 pts.) Determine the order of this reaction with respect to [B]. Explain your reasoning briefly. ' ‘fl-J : XW’rmj? 0.10)“ v n m _L 2.. UL.“ ‘ 2-, W 03:33 . m «MW 4 '4, (Mac a» [,6] c. (4 pts.) Write an expression for —d[A]/dt: " fig M [A] m “2' d. (3 pts.) Calculate the value of the rate constant and express it in appropriate units. 0 u ' I V 5 :15. \og/iztmjlfgj/Zz kfomszCO'lO] Z M A ~>L< 9w M3057] H Name 6. (17 pts. total) Answer the following questions about two compounds derived from the reaction of Glycine (Gly), Tryptophan (Trp), and Aspartic acid (Asp) shown below. A B HZN NH 0 I \y/ OH ' NH 0 . o o )L H OH O “wit” *4 EQWOH * n 0 NH; HZN A; u * 0H / N—H o o N—H \ / a. (4 pts.) Which of Compounds A or B does not correspond to a regular natural peptide and Why? B (3 a, mfiLM4 .3 “the Agra RS “NW cuddle b. (4 pts.) In the structure of Compound B above: - Indicate all chiral carbons with a star - Put a circle around one Sp2 hybridized atom - Put a square around one 3193 hybridized atom c. (4 pts.) Draw and label the strongest type of intermolecular force between the side chains of Asp and Arg in peptide A? i on or! O" 'H“ O “(in m , HC Z I, M l V“ .- "Zt: Z _<% ‘1~Hfg>—7+IVYK0H“ 3g N H d. (3 pts.) Explain why the side chain in tryptophan is not basic although it contains nitrogen. 77“: 5; 6&4}, M a 4w~§wwwrzwe ufiJEZTLLKawfi-ng (I? Lerzéew/g 7%. 2124:; em ” (“5' 6:» a: M?” fag“) film «1.5;: W fl e. (2 pts) What is the type of reaction called, that can cleave the above peptides into a dipeptide and an amino acid. W Name 7. Able Chemist carried out the decomposition of hydrogen peroxide at the same concentration at two dijfirent temperatures. Able recorded the data in a table, but carelessly forgot to record one of the temperatures. Able does remember that the lower temperature was 25 °C. H202 (6W) 9 2 H20 (1) + 02 (8) a) (5 points) Able graphed the data, as shown. On the graph, label the line corresponding to 4” the higher temperature and the line corresponding to the lower temperature. Explain! A» 4W 4 I/ié £ng do ruin via 2pc [ 2%0 3d) «in 450 a, W... M (24/ 7" b) (6 points) What is the order of reaction with Able’s Kinetics Data A respect to hydrogen peroxide? Briefly explain [H202] 25 [H202] mm] °C T2 your choice. Determine the two rates constants [ ‘ from the plot from Able’s data table below. 712». demxzfawt ea , (:4 Ln [AV/£02 J )4 774 ' e 7 “'k T’ 25°C -’ the; = @1030 6“" 1:? [0,0249] 2 C0, 20W] (“50) k = 4:90 '/o '2 W” = "9400704 5” c) (5 points) The activation energy for the decomposition has been determined to be 75.3 l<J/mol. Calculate at what other temperature Able did the other experiment. 3/? 2'/0’¢:: (O. ’20]7)C 44%) «La—E @395'3k3/Mi: 363029;. ‘3. R TL " T1“ 2%.l‘3tt Wt pm < lent/0”“ A ’HSBeo "L, Mm’Lfi "33 “0'3 {£31451 ' ’ Name Part C. Mastery Questions. Answer ONE of the following two questions. On the first page of the exam circle the question you want graded. 8. (l 9pts) The hydroxyl radical (OH') is one of the most important reactive species in the atmosphere. Below are three elementary reactions that involve OH: RXN l: °OH + CHC13 —> H20 + 'CC13 RXN 2: 'OH + OH —> H202 RXN 3: H202 —> 2 ‘OH a) (3pts.) State for each elementary reaction whether it is unimolecular or bimolecular. RXle MW RXNZ: \ RXN 3: AMAAXM b) (3 pts.) Can a molecule of hydrogen peroxide exist as both the structure on the left AND the structure on the right? If so, how does it get from one for to the other? 0/ of, VQL‘mnéir . c) (3 pts.) Which structure of hydrogen peroxide above is more consistent with the information that hydrogen peroxide has a dipole of 2.0D? Circle it and briefly explain your choice. M 5? WWVWVMK , 0 A e, 977 ,1 j fair“ #54 flyirflweaam “ it: "fligafiflwffiqq O “72/ fir: (This problem continues on the next page) W . w as 4 m A Name Two energy versus reaction coordinate diagrams are shown below. HO” +7: HQ, d) (2 pts) Draw the activation energy into both diagrams. e) (4 pts.) Which diagram corresponds to RXN 1 and which one to RXN 2? Use differences in activation energy that you expect between the two reactions as reasoning. Diagram A corresponds to RXN 2— .Reason: pm [is W flag/(7,}ng 1434,33, r r, i w» ' ' ‘ zi‘ i y . g a I/ma- Paw/6t Cafe elevate? émmézm‘ae! ‘ r ‘ ' Diagrachorresp’onds toRXN / .Reasony' m {taxi}: ref/W m /7/' (A? "a a: {/1 v5" t) (4 pts.) Draw the reactant and product molecules into the diagrams and explain what the reaction coordinate corresponds to in each diagram. Z; MA Mlfl¢iémfla (a?) /z{e a “’0 2/0‘ -a l/C%_ A” 7. Name 9. (19 points) This question is about poly(B-hydroxybutyrate), ‘ 7 O a new biodegradable polymer researched by Procter & Gamble Co. B-hydroxybutyric acid monomer and its condensation * polymer are produced as energy storage molecules by various HO OH bacteria. B-hydroxybutyric acid a.) (4 points) Draw B-hydroxybutyric acid using wedges and dashed wedges to indicate the three dimensional structure around the carbon with an asterisk (*). Does B— hydroxybutyric acid have any optical isomers? b.) (5 points) Poly(B—hydroxybutyrate) is produced by heating B—hydroxybutyric acid and removing water. Draw two repeat units of polymer and indicate the repeat unit by“ enclosing it in brackets. Circle and label the functional group that is the linkage between themonomers. r ' " " ' "' ' ' ' ' NOTE: You DO NOT need to draw the polymer in three dimensions. Name c.) (2 points) Name two important factors that govern the physical properties of macromolecules. 0.. 0&4“, a flaw Pl d.) (4 points) Professor M. really likes the idea of making poly([3-hydroxybutyrate) plastic bags, except that he has to control how big each polymer chain becomes in the condensation polymerization in order to make the polymer useful, In order to do so, he adds some ethanol and acetic acid (shown below) to control the size of the chains. Can you explain why? III 0 H3c—c—OH HacJLOH H Ethanol Acetic acid 7:: (am/6M Malagasy ~CQOZ/ {6/% r /fi;fiW/Z V/b 7M6 M '%Jé’ AW 2% W 2 flat/at! a 7 _ frag/65M mw/ (:pr fl aw /% @zamta”% e) (4 points) Draw how app ’opriate orbitals of tie carbon and oxygen atom of the carbonyl group in acetic acid form a double bond. Label the relevant bonding orbitals clearly. Clearly state in words how the double bond is formed. CAM/3;, a/mgz‘aw Mafia“ ,5 / (ham-1 V, J/‘the‘éfez. w‘l ...
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Chem_2009FALL_Exam 2 Key - Name TA Section Chemistry 109...

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