Chem_173B_Midterm_Exam_2008_Key

Chem_173B_Midterm_Exam_2008_Key - Name: Chem 173B/268B...

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Page 1 of 4 Name: Midterm Exam Score: /45 Chem 173B/268B W2008 Prof. S. Scott Time allotted: 50 mins Instructions: Please write and draw clearly. Illegible answers will not be graded. 1. (8 points) Cite a common modern use for the four of the following five elements (not necessarily in elemental form): (a) Li lithium batteries, lithium pharmaceuticals (Li 2 CO 3 ), automotive lubricants (b) Be neutron moderator for nuclear reactors, aerospace alloys, X-ray windows (c) B borax washing powder, Pyrex glass, Boron Neutron Capture Therapy (d) Pb lead batteries (lead paint pigments, leaded gasoline are not in use anymore, but are close enough to constitute acceptable answers) (e) Bi Pepto-Bismol (bismuth subsalicylate) 2. (8 points) Provide brief (1 sentence) explanations for four of the following five statements: (a) CaCl 2 is deliquescent, while CaCO 3 is not. The Ca 2+ ion has a high hydration enthalpy, and the lattice energy for CaCl 2 is low enough that the salt can take up water vapor from the air (note this is not the same as solubility in liquid water). In contrast, the lattice energy for CaCO 3 is high so it does not hydrate spontaneously in air. (b) Pt(PMe 3 ) 4 reacts spontaneously with 2 equivalents of bis(dimethylphosphino)ethane, liberating all of its PMe 3 . The complex with the bidentate bis(phosphine) ligand is entropically favored over the monodentate phosphine ligand, called the chelate effect. (c) SiCl
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Chem_173B_Midterm_Exam_2008_Key - Name: Chem 173B/268B...

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