1127e2key.pdf - UJ Chemistry 1127 Hour Examination 2 UConn...

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Unformatted text preview: UJ Chemistry 1127 Hour Examination 2 March 23, 2018 UConn Stamford Name: Section Signature: PLEASE READ THE FOLLOWING INSTRUCTIONS Please do not begin the exam until you are asked to do so. The exam consists of pages 1-5. Please check that they are all present and write your name on every page. There is a separate page with equations and a periodic table with in the exam. The scantron sheet must be filled in with your name and in #2 pencil ONLY. Ink will not scan. If you must erase, do so cleanly. If you want a record of your answers, record them on the exam as well. The scantron sheet will not be returned to you. Make sure you complete the written portion of the exam in blue or black indelible ink. Exams with work in pencil or which show evidence of white-out, erasable ink, etc. will not be re-graded in case of grading error. Please show all work, no matter how trivial. Partial credit will only be awarded where work is clearly shown and can be followed. Use the back of the pages for scratch work. No scratch paper is allowed. Pay attention to significant figures and units throughout the exam. -—— Part 1. Write your answer in the blank on the answer sheet. (32 points; 2 each) 1. What is the name of K2Cr04? A. potassium chromide C. potassium dichromate notassium chromate D. potassium chromiulel) oxide E. potassium chromium(|l|) oxide 2. Which of these in aqueous solution is called phosphoric acid? A. HPO42' B. H2PO4‘ @490. 0. PH; E. H3P03 3. Which of the following contains both ionic and covalent bonds? A. NaI.Na3P04 c. P205 0. H2C03 E. CHCI3 4. Which of the following atoms cannot form an expanded octet? A.S B.Se C.Rn.C E.Te 5. A molecule with a central atom surrounded by two lone pairs and four single bonds will show which type of hybridization? ‘ A. sp B. sp2 C. sp3 D. sp3d I C; 5de2 6. Referring back to #5, which geometry is predicted for the central atom? A. linear B. trigonal planar C. trigonal bipyramidala square planar E. octahedral 7. How many pi electrons are there in a double bond? A.0 B.1 C.2 D.4 ES 8. Select the strongest bond in the following gr up. A. c—s B. c—o c. c=c a CEN E. C—F 9. In which ofthese substances are the atoms held together by polar covalent bonding? A. SrCIz B. CsCl @CIF D. TiF2 E. 53 10. The covalent bond with the greatest polarity would form in which ofthese atom pairs? A. Br—Br 3.5—0 C.C—P D.C-O ©3—o 11 Which molecule has the largest dipole moment? (2 A. l—l F B. HI C. HBr D. HCI E. All have the same dipole moment 12. Which of th- e molecules has an atom with an expanded octet? A. HCI 6mm; c. ICI D. NCIa E. CI; Na me 13. What is the total number of electron pairs around the central atom in a trigonal pyramid (such as ammoni NHg)? A.5 ‘4 cs 0.2 EB 14. How many electrons can occupy a hybrid orbital? A.10 B.8 C.6 D.4 (32 15. What geometry is formed by mixing 5, p and d orbitals and has more than two different bond angles? A. trigonal planar B. tetrahedral C9 trigonal bipyramidal D. octahedral 16. Which molecule would you expect to have the greatest percentage ionic character? 0 HF B. HCI C. HBr D. HI E. CH4 Part 2 — All work must be clearly shown. Answers without work receive no credit. 1. (4 points) For the following Lewis structures, indicate whether the molecule is polar or nonpolar. Nonpolar or polar Molecule 2. (8 points) Write the resonance structures for the molecule 50;, indicating the formal charges. Use the octet rule only— not expanded octets. —" _. t.‘ :0 age—0 ‘ -. __..- ll .5 .4 "H V % +1 ”0 .. . __ 2..| P a. g. .35 T .0 t” a l __ __.—__.: -1”— N a m e 3. (10 points) An incomplete Lewis structure is shown for the molecule called styrene, which is used to make polystyrene plastic, commonly used in everyday objects marked with a "6” recycling symbol. Complete the Lewis structure above. The structure will not be graded but it will need to be complete to answer the following questions. A. A How many double bonds are recluired to complete the structure? a. B. 5% What is the hybridization of each carbon in the 6-membered ring? A‘ZWWhat is the molecular geometry around each carbon in the 6-membered ring? D. 5 F L What is the hybridization ofthe last carbon (the one with two H’s attached? @ How many lone pairs are required to complete the Lewis structure? 4. (12 points) A compound consists of 29.48% Ca, 35.21% Ti and 35.30% 0 by mass. What is its simplest formula? - CA at m C“ *‘O.q'3§$ 1% “L31 . LLUDKj Zgr'Z/ll th \c jam/bk Tl : 0.135% ”3/ij L 35303 O x ‘M O = ”9.0030 Name 5. (12 points) You have on hand a 250.0 mL volumetric flask and a supply of sodium hydrogen carbonate (NaHCOa, molar mass = 84.01 g/mol). What mass of NaHCO; do you need to dissolve and dilute to 250.0 mL to produce a solution that is 1.55 M in NaHCOs ? BUICOL «lugng K XLé‘ZElj/v : 32M 5. Name L m l (10 points) Concentrated HCI is 12.0 M. What volume of concentrated HCI, when diluted to 2.00 L will produce a solution that is 6.0 M in HCI? LON—M (.owl X 1L 1 M' l. T (3 l7, Mbl (12 points) Automobile air conditioners commonly contain a refrigerant known as R-134A, which contains carbon, hydrogen and fluorine. This compound is analyzed by combustion; in the analysis a 12.50 g sample of R-134A produces 9.31 g of atomic fluorine (F), 10.77 g C02 and 2.208 g of water A. What' IS its simplest formula? (3) «Ml/m — owiqml l.i:/o 2%} ' B."< The molar mass fR- 134A Is 102.03 g/mol. What' IS the molecular formula? 0.0 s/ml lot/l5"! = 2 9 d 5i BONUS — 10 points, all or nothing. Work must be logically correct and the answer must be exact. Show work on back of this page. A sample is analyzed for chloride content by titrating it with silver nitrate (AgNog) and using potassium chromate (K2004) as an indicator. if a sample weighing 0.1442 g required 17.42 mL of 0.09054 M AgNOa to reach the equivalence point, what is the percentage chloride by mass in the sample? ' Ag+ (aq) + Cl'(aq) 9 AgCl (s) , ml" 3%? ti 2 «3. (NW ml ix iii—me K ‘31 0.911% LX B L, Ara iMiA'j mic/(K :Waclm .. 5 ._ | . P. a g. e __ To t a. "l __ __ — —‘ __ :: : Name 0 1 2 3 .4 5 6 1 2 3 4 5 7.. 1 1 1 1 1 1 1 Name Chemistry 1127 Hour Examination 2 March 23, 2018 UConn Stamford Name: Section Signature: PLEASE READ THE FOLLOWING INSTRUCTIONS Please do not begin the exam until you are asked to do so. The exam consists of pages 1-5. Please check that they are all present and write your name on every page. There is a separate page with equations and a periodic table with in the exam. The scantron sheet must be filled in with your name and in #2 pencil ONLY. ink will not scan. If you must erase, do so cleanly. If you want a record of your answers, record them on the exam as well. The scantron sheet will not be returned to you. Make sure you complete the written portion of the exam in blue or black indelible ink. Exams with work in pencil or which show evidence of white-out, erasable ink, etc. will not be re-graded in case of grading error. Please show all work, no matter how trivial. Partial credit will only be awarded where work is clearly shown and can be followed. Use the back of the pages for scratch work. No scratch paper is allowed. Pay attention to significant figures and units throughout the exam. --- Part 1. Write your answer in the blank on the answer sheet. (32 points; 2 each) 1. What is the name of K2004? A. potassium dichromate B. potassium chromide C. potassium chromate D. potassium chromiulel) oxide E. potassium chromium(|l|) oxide 2. Which of these in aqueous solution is called phosphoric acid? A. HPO42' B. H2PO4' C. H3P03 D. PHa E. H3P04 3. Which of the following contains both ionic and covalent bonds? A. Nal B. P205 C. N83P04 D. H2C03 E. CHCIa 4. Which ofthe following atoms cannot form an expanded octet? A.S B. C C. Rn D.Se E. Te 5. A molecule with a central atom surrounded by two lone pairs and four single bonds will show which type of hybridization? A. 5de2 B. sp C. sp2 D. sp3 E. spad 6. Referring back to #5, which geometry is predicted for the central atom? A. linear B. octahedral C. trigonal bipyramidal D. square planar E. trigonal planar 7. How many pi electrons are there in a double bond? A.6 B.4 C.2 [11 ED 8. Select the strongest bond in the following group. A. C-S B. C—O C. CEN D. C=C E. C—F 9. In which of these substances are the atoms held together by polar covalent bonding? A. SrClz B. CIF C. CsCl D. Tin E. 53 10. The covalent bond with the greatest polarity would form in which of these atom pairs? A.Br—Br B.B—O C.C—P D.C—0 E.S-O 11 Which molecule has the largest dipole moment? A. HI B. HCI C. HBr D. HF E. All have the same dipole moment , 12. Which ofthese molecules has an atom with an expanded octet? A. HCI B. NCI; C. ICI D. AsCIs E. Clz 1| p ag' La; T a i a i " ' _; Q; 4% Name 13. What is the total number of electron pairs around the central atom in a trigonal pyramid (such as ammonia, NH3)? A.5 3.6 cs 0.2 @4 4. How many electrons can occupy a hybrid orbital? A. 2 B. 4 C. 6 D. 8 E. 10 15. What geometry is formed by mixing 5, p and d orbitals and has more than two different bond angles? {((filftrigonal bipyramidal B. tetrahedral C. trigonal planar D. octahedral 16. Which molecule would you expect to have the greatest percentage ionic character? A. HCl B. HBr ‘ C.)HF D. HI E. CH4 V Part 2 —All work must be clearly shown. Answers without work receive no credit. 1. (4 points) For the following Lewis structures, indicate whether the molecule is polar or nonpolar. Nonpolar or polar Molecule 2. (8 points) Write the resonance structures for the molecule 502, indicating the formal charges. Use the octet rule only — not expanded octets. ._.. -2. | Pa gel-to ta Name 3. (10 points) An incomplete Lewis structure is shown for the molecule called styrene, which is used to make polystyrene plastic, commonly used in everyday objects marked with a "6” recycling symbol. Complete the Lewis structure above. The structure will not be graded but it will need to be complete to answer the following questions. A. How many double bonds are required to complete the structure? B. ' What is the hybridization of each carbon in the 6-membered ring? C. What is the molecular geometry around each carbon in the 6-membered ring? I D. What is the hybridization ofthe last carbon (the one with two H’s attached? E. How many lone pairs are required to complete the Lewis structure? 4. (12 points) A compound consists of 29.48% Ca, 35.21% Ti and 35.30% 0 by mass. What is its simplest formula? . . 3...|.p. rang eTotal__ ____ Na me 5. (12 points) You have on hand a 250.0 vaolumetric flask and a supply of sodium hydrogen carbonate (Na HC03, molar mass = 84.01 g/mol). What mass of Na HCOa do you need to dissolve and dilute to 250.0 mL to produce a solution that is 1.55 M in NaHC03 ? 6. (10 points) Concentrated HCI is 12.0 M. What volume of concentrated HCI, when diluted to 2.00 L will produce a solution that is 6.0 M in HCI? 7. (12 points) Automobile air conditioners commonly contain a refrigerant known as R-134A, which contains carbon, hydrogen and fluorine. This compound is analyzed by combustion; in the analysis, a 12.50 g sample of R-134A produces 9.31 g of atomic fluorine (F), 10.77 g C02 and 2.208 g of water. A. What is its simplest formula? B. The molar mass of R-134A is 102.03 g/mol. What is the molecular formula? .... .. .. .. .4. I- g). "a' ...g. "e" "T" .0. ..t. .3. ...' .. :. ~... ; . —. ...: Name BONUS—- 10 points, all or nothing. Work must be logically correct and the answer must be exact. Show work on back of this page. A sample is analyzed for chloride content by titrating it with silver nitrate (AgNOa) and using potassium chromate (K2004) as an indicator. Ifa sample weighing 0.1442 g required 17.42 mL of 0.09054 M AgN03 to reach the equivalence point, what is the percentage chloride by mass in the sample? Ag+ (aq) + Cl' (aq) 9 AgCl (5) '5'] is a get at" 5 i "L L“ LL Name Name ...
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