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UT CH 301 - Exam 3

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001version last name first name signatureBIBERDORF CH301unique: 48815, 48830Exam 3Fall 2019Nov 6, 2019Wed 5:30pm - 7pmRemember to refer to the Periodic Table handout that is separate from this exam copy.NOTE: Please keep this exam copy intact (all pages still stapled - including this cover page). Youmust turn in ALL the mat erials that were distributed. This means that you turn in yourexam copy (name and signature included), bubble sheet, free response (name and versionnumber included), periodic table handout, and all scratch paper. Please also have yourUT I D card ready to show as well.Version 001 – Exam 3 - F19 – biberdorf – (48815) 2This print-out should have 20 questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore answering.001 4.0 pointsRank these single bonds from least polar tomost polar:C − O, H − F, C − S, Br − Br1. H − F < C − S < C − O < Br − Br2. Br − Br < H − F < C − S < C − O3. Br − Br < C − O < C − S < H − F4. Br − Br < C − S < C − O < H − Fcorrect5. H − F < C − O < C − S < Br − BrExplanation:Br-Br is the least polar, and H-F is the mostpolar, so the choices are reduced to two possi-bilities. O is the second-most electronegativeelement of al l, so C-O is a more pol ar bondthan C-S.002 4.0 pointsThe polyatomic ion SO2−3has ?electronicgeometry and ?molecular geometry.1. tetrahedral; trigonal pyramidal correct2. tetrahedral; octa hedral3. trigonal planar; trigonal planar4. trigonal bipyramidal; T-shaped5. tetrahedral; tetrahedral6. trigonal bipyramidal; trigonal planarExplanation:SO2−3has 26 total valence electrons. 6 va-lence electrons are contributed by S, 18 (3atoms at 6 electrons each) valence electronsare contributed by O, and there are 2 addi-tional electrons owing to the −2 charge thision has. In drawing the Lewis structure forthis io n, we discover that the central atom Shas single bonds to each O atom and a lonepair. This makes the general formula for thision AB3U, which has a tetrahedral electronicgeometry but a trigonal pyramidal moleculargeometry.003 4.0 pointsDraw the Lewis dot structure for the arsenateion, AsO3−4. How many resonance structureswill this ion have?1. 52. 33. 4 correct4. 15. 2Explanation:There is one double bond and three singlebonds in the Lewis dot structure. The otherthree resonance structures wo ul d show thedouble bond on each of the other three oxygenatoms.As OOOObbbbbbbbbbbbbbbbbbbbbb3−004 4.0 pointsAn atom of a certain element has a total of16 electrons. An ion of the same elementhas a total of 18 electrons. Which statementbelow best describes the difference betweenthe atom and the ion?1. The ion and the atom are the same size,but the atom has no net charge.2. The ion is la r ger than the ato m and has apositive charge.3. The ion is smaller than the atom and hasa positive charge.Version 001 – Exam 3 - F19 – biberdorf – (48815) 34. The i o n is smaller than the atom and hasa negative charge.5. The ion is larger than the atom and has anegative charge. correctExplanation:As the ion has more electrons than the neu-tral atom, the ion will be negatively charged.Negative anions are always larger in size thantheir respective neutral atoms due to moreelectron-electron repulsion.005 4.0 pointsWhich of these is closest to the bond angle ina sulfur dioxide molecule?1. 88◦2. 120◦3. 109.5◦4. 107◦5. 90◦6. 119◦correctExplanation:The best structure for SO2has three RHEDsaround the sulfur (two double bonds and onelone pair). This gives a trigo nal planar elec-tronic geometry with bond angles of 120◦, butthe presence of a lone pair will cause the bo ndangle to slightly decrease. Thus, the bondangle in SO2will likely be closest to 119◦.006 4.0 pointsConsider a diatomic molecule that has 8 va-lence electrons. What is the b ond order of themolecule if you use Molecular Orbital theory?1. 1.52. 13. 2 correct4. 2 .55. 06. 3Explanation:Regardless o f which orbital diagram you use,you will have 6 electrons in bonding orbitalsand 2 electrons in anti-bonding orbitals. BO=(6−2)2= 2007 4.0 pointsWhich o f the following are conclusions thatcan be made from the completed molecularorbital diagra m for OF+? (Use the same MOdiagram t hat you would use for O2for thismolecule.)I. There is at least one electron in a π∗2porbital.II. The bond order is 2.III. The molecule is paramagnetic.1. I, I I, and III correct2. I and III only3. II and III only4. I and II only5. I onlyExplanation:Fill in the correct diagram with the 12 valenceelectrons (6+7-1):σ∗2pπ∗2p↑ ↑π2p↑↓ ↑↓σ2p↑↓σ∗2s↑↓σ2s↑↓008 4.0 pointsRank the following compounds in order ofincreasing melting point:Version 001 – Exam 3 - F19 – biberdorf – (48815) 4CO2, NaCl, H2O, KCl, CaCl21. CO2< NaCl < H2O < KCl < CaCl22. CO2< H2O < KCl < NaCl < CaCl2correct3. NaCl < CaCl2< KCl < H2O < CO24. KCl < CaC l2< NaCl < CO2< H2O5. H2O < CO2< NaCl < KCl < CaCl26. KCl < NaCl < CaCl2< CO2< H2O7. H2O < CO2< KCl < CaCl2< NaCl8. CaCl2< CO2< H2O < KCl < NaClExplanation:009 4.0 pointsConsider an orbi tal energy diagram for amolecule with a central atom that has sp2hybridization. There is one electron in eachof the sp2orbitals. If the 2p orbital is empty,from which group would you expect to findthe central atom on the periodic table?1. Group 72. Group 3 correct3. Group 54. Group 25. Group 16. Group 67. Group 88. Group 4Explanation:There are three unpaired electrons (one ineach sp2orbital). This molecule would likelyhave a central atom from Group 3. Example:BCl3010 4.0 pointsWould you expect for CH3OH or CH3CH2OHto have a higher vapor pressure? Why?1. CH3OH because it can form fewer hydro-gen bonds than CH3CH2OH.2. CH3CH2OH because it has more hydro-gen bonds than CH3OH.3. CH3CH2OH because it is mo r e polari z-able than CH3OH.4. CH3OH because it can form more hydro-gen bonds than CH3CH2OH.5. CH3OH because it is less polarizable thanCH3CH2OH. correct6. CH3OH because it is more pol arizablethan CH3CH2OH.Explanation:CH3OH is a smaller molecule thanCH3CH2OH. Therefore it will be less polariz-able and have a higher vapor pressure. Theyboth exhibit hydrogen bonds.011 4.0 pointsWhich of the following liquids would you ex-pect to have the highest boiling point?1. N22. GeH43. CH3CH2CH2CH2NH2correct4. H2Se5. PCl3Explanation:CH3CH2CH2CH2NH2can exhibit hydrogenbonding and has strong dispersion forces,therefore we wo ul d expect for it t o


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