CH301 Fall 2013 Vanden Bout LaBrake Unit 3 Exam 25 POINTS Name KEY UT EID VERSION Questions on front and back Show work for partial credit Your work and answers must fit in the boxes provided for each question Responses outside the boxes will not be graded 1 8 points a Fill in the Molecular Orbital MO diagram for N22 3 pts for correct diagram b Identify on the MO diagram the location of the HOMO and the LUMO 2 pts 1 for HOMO 1 for LUMO for correct analysis based on the filled out MO c State the bond order B O 0 5 bonding electrons antibonding electrons B O 0 5 6 2 0 5 4 2 B O 2 2 pts for correct analysis based on the filled out MO d Is N22 expected to be paramagnetic or diamagnetic Diamagnetic 1 pts for correct analysis based on the filled out MO 2 8 points Iodine exists as a solid up to 114 C at 1 atm pressure Brass an alloy of copper and zinc has a melting point of 900 C at 1 atm pressure Fully describe each solid Identify the type of solid and report on their physical properties macroscopic view Provide a microscopic description for each solid include a picture and description of the forces that hold the substance together in the solid phase 1 for each correct microscopic picture 2 pts total 1 for type of solid 2 pts total 1 for correct IMFs microscopic view of the solid 2 pts total 1 for correct macroscopic property given 2 pts total Iodine Questions on front and back Some possible pictures Type of solid Molecular solid Types of IMFs microscopic view Dispersion Forces only Macroscopic properties must include at least one Brittle hard not a conductor low BP Brass Some possible pictures Type of solid Metallic solid Types of IMFs microscopic view Metallic bonds with a sea of electrons delocalized Macroscopic properties must include at least one Malleable ductile good conductor shiny 3 9 points A On your first day in the laboratory your boss provides you with four unmarked vials She was able to evaluate the melting and boiling points of each compound but needs your help identifying the molecule in each vial The four possible chemicals are benzene naphthalene acenaphthene and pyracene Please identify the compound in each vial as well as its phase solid liquid or gas at room temperature Benzene Naphthalene Acenaphthene Questions on front and back Pyracene Vial Number Compound Identity Melting Point C Boiling Point C Phase at Room Temperature Vial 1 Naphthalene 80 218 Solid Vial 2 Pyracene 214 363 Solid Vial 3 Benzene 5 5 176 Liquid Vial 4 Acenaphthene 93 279 Solid 2 pts for compounds 1 if only half correct 2 pts for correct phases 1 if only half correct B What is the dominant intermolecular force for the compounds listed in part A The dominant force is dispersion aka London dispersion forces induced dipoles van der waals forces 2 pts for correct IMF C Of the four compounds which has the strongest intermolecular forces Why Pyracene has the strongest IMFs because it is the largest and therefore the most polarizable 3 pts total 1 for correct compound 2 for correct explanation of polarizable Questions on front and back
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