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chem 109a exam 1-example-with keys

chem 109a exam 1-example-with keys - Chem 109A InClass Exam...

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Unformatted text preview: Chem 109A InClass Exam 1 Wed., January 20, 2010 Name: ________________________ Perm number: _________________ Name: ____________________________________ Perm number: __________________ Question 1) multiple choices (50 pts) 2) nomenclature (20 pts) 3) Rank properties (8 pts) 4) short answer questions (22 pts) Total (100 pts) Your score 1. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) When a small amount of hexanoic acid [CH3(CH2)4CO2H, pKa~4.8], is 1) _______ added to a separatory funnel which contains the organic solvent diethyl ether and water with a pH of 2.0, it is found mainly in the __________ phase as __________. A) ether; CH3(CH2)4CO2 B) water; CH3(CH2)4CO2H C) ether; CH3(CH2)4CO2H D) water; CH3(CH2)4CO2 E) none of the above 2) What is the conjugate base of CH3NH2? A) NH4+ B) NH2 C) CH3NH D) CH3NH3+ 3) _______ 3) Which of the following is closest to the C-O-C bond angle in CH3-O-CH3? A) 180 B) 120 C) 90 D) 160 E) 109.5 4) Which of the following ions is the strongest acid? A) HO B) HSO4 C) H2O D) H3O+ E) H 5) The lone-pair electrons of the methyl anion occupy a __________ orbital. 5) _______ A) s B) sp3 C) sp2 D) p E) sp 4) _______ 2) _______ 6) What are the formal charges on nitrogen and the starred oxygen atom in the following molecule? 6) _______ A) N= +1, O = 0 B) N = +1, O = -1 C) N = -1, O = -1 D) N = -1, O = 0 E) N = +1, O = +1 7) What is the pH of a 0.1 M solution of HCl? (Note: pKa for HCl is -6.) A) -8 B) 6 C) -1 D) -6 E) 1 8) _______ 8) Which of the following elements does this electronic configuration represent? 1s2 2s2 2p5 A) N B) F C) O D) C E) Al 9) Which of the following covalent bonds has the largest dipole moment? A) H-N B) C-H C) H-F D) C-C E) C-O 10) Choose the correct hybridization for the atom indicated in the molecule below. CH3CH2CH2CH3 A) sp3 B) sp2 C) sp D) none of the above 11) Which of the following is the most likely electronic structure for C2H2? A) B) HCCH C) 7) _______ 9) _______ 10) _____ _ 11) _____ _ D) E) 12) Which of the compounds below bond predominantly via ionic bonding? 12) _____ _ A) NH3 B) KCl C) CF4 D) both A and B E) both B and C 13) How many unpaired electrons are present in the isolated carbon atom (atomic number = 6)? A) none B) one C) two D) three E) four 14) Among the butane conformers, which occur at energy minima on a graph of potential energy versus dihedral angle? A) eclipsed only B) anti only C) gauche and anti D) eclipsed and totally eclipsed E) gauche only 15) Which of the following is the most stable conformation of bromocyclohexane? 13) _____ _ 14) _____ _ 15) _____ _ A) I B) II C) III D) IV E) V 16) Which of the following is the staggered conformation for rotation about the C1C2 bond in the following structure? 16) _____ _ A) I B) II C) III D) IV E) V 17) _____ _ 17) Which of the following is a tertiary amine? A) B) C) D) E) _ 18) Which of the following has the greatest solubility in CH3CH2CH2CH3? 18) _____ A) CH3OH B) CH3NH2 C) CH3O- Na+ D) (CH3)3CH E) CH3OCH3 19) Which of the following statements about the conformers that result from rotation about the C2-C3 bond of butane is correct? A) The highest energy conformer is one in which methyl groups are eclipsed by hydrogens. B) Torsional strain is absent in the eclipsed forms. C) The gauche conformer is an eclipsed one. D) Steric strain is absent in the eclipsed forms. E) none of the above 20) Which of the following is an sp2 hybridized carbon? A) B) C) CH3 D) A and B E) A, B and C 21) Which of the following molecules has a net dipole moment of zero? A) 19) _____ _ 20) _____ _ 21) _____ _ B) C) D) E) 22) Which of the following is the strongest acid? A) CH3OCH3 B) CH3CH2OH C) CH3NHCH3 D) CH3CCH E) CH3CHCH2 23) Which carbon(s) in the following molecule is (are) sp hybridized? 22) _____ _ 23) _____ _ A) carbon 4, 5 B) carbon 2 C) carbons 1, 3 D) carbons 4 E) carbon 1 24) Which of the compounds below will form hydrogen bonds between its molecules? A) CH3NHCH2CH3 B) CH3CH2CH2F C) CH3CH2OCH3 D) (CH3)3N E) CH3CH2CH2CH3 lj 24) _____ _ 25) Which of the following is not a conjugate acid-base pair? A) -OH, O2 B) H2O, HO C) H2O, H3O+ D) HSO4-, H2SO4 E) NO3-, NO2 25) _____ _ 2. Nomenclature (20 pts) 1) Please provide common names for the following compounds (5 pts) methyl alcohol diisopropyl ether ethyl iodide methylamine isobutane 2) Please provide IUPAC names for the following structures (10) 3) Please indicate whether the following IUPAC name is correct or not. If incorrect, provide the correct name (5pts) a) 3methylbutane incorrect. 2methylbutane b) 4methoxy3chlorocycloheptane incorrect 1chloro2methoxycycloheptane c) hexan2ol incorrect. cyclohexan1ol or cyclohexanol 3. Rank according to the indicated properties using 1 for the most and 4 for the least (8 pts) a) Acidity HCl HI HF HBr 3 1 4 2 b) solubility in H2O 2 3 4 1 c) boiling point (1 for the highest and 4 for the lowest) 1 3 2 4 d) molecular dipole moment 4 2 1 3 4. SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question (. 1) _____________ 1) Draw the Kekul structure for each of the following: a. CH3CH2OH b. CH3CHO c. (CH3)3C+ 2) Would you predict trifluoromethanesulfonic acid, CF3SO3H, to be a stronger or weaker acid than methanesulfonic acid, CH3SO3H? Explain your reasoning. 2) _____________ 3) Why is the CH bond in ethene (H2CCH2) shorter and stronger than the CH bond in ethane(CH3CH3)? 3) _________ 4) If H2O has a pKa value of 15.7 and HF has a pKa value of 3.2, which is a stronger base, HO- or F-? Explain. 5) The Kekul structure of pentane is shown below. Draw the condensed structural formula which corresponds to this Lewis structure. 4) _____________ 5) _____________ 6) Provide a representation of the gauche conformer of butane. 6) _____________ 7) Write a completed equation for the acid-base pair shown below. 7) _____________ HCO2H + -NH2 8) Covalent bonds may be polar or nonpolar. What property of the atoms forming a given bond determines this? please define the property 8) _____________ 9) Draw the most stable conformation of cis-1-isopropyl-2-methylcyclohexane. 10) Estimiate the equibrium of the following acid and base reaction, is it: (a) >1 b) <1 c) =1 Why? 11) Draw the Newman projection of the most stable conformation that results due to rotation about the C2-C3 bond in 2,3-dimethylbutane. 9) _____________ 10) _____________ 11) _____________ 1. Multiple choices: 1) C 2) C 3) E 4) D 5) B 6) A 7) E 8) B 9) C 10) A 11) B 12) B 13) C 14) C 15) C 16) A 17) C 18) D 19) E 20) B 21) E 22) B 23) A 24) A 25) E 4. Short Answer questions 1) 2) Trifluoromethanesulfonic acid is a stronger acid. Compare the strengths of the conjugate bases and remember that the weaker the base, the stronger the conjugate acid. In the case of the trifluoro derivative, the presence of the highly electronegative fluorine atoms serves to delocalize the negative charge to a greater extent. This additional delocalization makes trifluoromethanesulfonate a weaker base. 3) The length and strength of a CH bond depends on the hybridization of the carbon atom. The more s character in the hybrid orbital used by carbon to form the bond, the shorter and stronger the bond. This is because an s orbital is closer to the nucleus than is a p. Ethene uses carbon sp2 hybrid orbitals (1/3 s character) to make its carbon-hydrogen bonds while ethane uses carbon sp3 (1/4 s character). 4) HO- is a stronger base than F- because HF is a stronger acid than H2O, and the stronger the acid the weaker its conjugate base. 5) CH3(CH2)3CH3 6) 7) HCO2H + -NH2 HCO2- + NH3 8) electronegativity : a measure of the intrinsic ability of an atom to attract electrons in a covalent bond. ...
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