chemistry PRACTICE EXAM - CHEM 1000 A, V Midterm Test #3,...

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Midterm Test #3, February 9, 2007. Part A. Answer each question with a few sentences or equations where necessary. (5 Marks each) 1. Name the strongest intermolecular force in each of the following pairs of species: Species Strongest Intermolecular Force Two Xe atoms Dispersion forces H 2 O and NH 3 Hydrogen-bonding Cu +2 and CS 2 Ion-Induced dipole forces Two CHF 3 molecules Dipole-dipole forces Two molecules of H 3 C C CH 3 O Dipole-dipole forces (not H-bonds) 2. Why does H 2 O (l) have a higher surface tension than CO 2(l) ? Since water is s polar molecule, the intermolecular potentials among water molecules are greater than among the (linear) non-polar CO 2 molecules. This stronger force in water results in a large difference in energy between molecules at the surface and those in the interior of the liquid. 3. Why does a 1.00 m solution of NaCl (aq) have a lower boiling point than a 2.0 m solution of a non-ionic solute? Although the number of particles in these two solution are the same, the Na + (aq) and Cl - (aq) ions form ion-pairs, effectively reducing the number of ions in solution, hence reducing the boiling point elevation. 4. Why is ice less dense than liquid water? The water molecules in ice are arranged in an open hexagonal structure, held in place by H-bonding. This open structure has a lower density than that of liquid water. 5. A piece of iron anodized with zinc metal will not corrode even if some of the iron metal is exposed to air and water. Why not? The oxidation of zinc is electrochemically preferred. The high energy electrons produced as a result of the zinc oxidation effectively prevent the oxidation of iron, which oxidizes at a lower potential than zinc. 6.
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chemistry PRACTICE EXAM - CHEM 1000 A, V Midterm Test #3,...

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