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Unformatted text preview: kamalska (mk23835) HW01 Quigley (104001) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A crystal of dry ice (solid CO 2 ) consists of molecules of CO 2 arranged at orderly po- sitions in a crystal lattice. The molecules are bonded intramolecularly by covalent C O bonds, and are held together in the crystal by weak intermolecular forces between the CO 2 molecules. This is an example of 1. an ionic crystal. 2. a molecular crystal. correct 3. a covalent crystal. 4. an amorphous substance. 5. a metallic crystal. Explanation: Molecular crystals are molecules held to- gether in a lattice by intermolecular forces: H bonds, London forces and dipole-dipole inter- actions. 002 10.0 points Surface tension describes 1. adhesive forces between molecules. 2. capillary action. 3. the forces of attraction between the sur- face of a liquid and the air above it. 4. the inward forces that must be overcome in order to expand the surface area of a liquid. correct 5. the resistance to flow of a liquid. 6. the forces of attraction between sur- face molecules of a solvent and the solute molecules. Explanation: Molecules in the interior of a liquid inter- act with molecules all around them, whereas molecules at the surface of a liquid can only be affected by those beneath the surface layer. This phenomenon leads to a net inward force of attraction on the surface molecules, con- tracting the surface and making the liquid behave as though it had a skin. Surface ten- sion is a measure of the inward forces that must be overcome to expand the surface area of a liquid. 003 10.0 points Rank the gas molecules CH 3 F , C 2 H 6 , H 2 O , H 2 , He in terms of increasing non-ideality based upon intermolecular interactions. 1. H 2 O , CH 3 F , C 2 H 6 , H 2 , He 2. C 2 H 6 , H 2 O , CH 3 F , He , H 2 3. H 2 , He , CH 3 F , H 2 O , C 2 H 6 4. None of these is correct. 5. He , H 2 , C 2 H 6 , CH 3 F , H 2 O correct Explanation: The intermolecular attractions, ranked from weakest to strongest, are London forces (also called van der Waals forces or induced dipoles), dipole-dipole interactions, hydro- gen bonding interactions, and ion-ion inter- actions. Strong intermolecular interactions cause molecules to stick to one another, and thus deviate from ideal behavior. In gen- eral, the larger the molecule, the greater the total intermolecular forces. H 2 O has two O H bonds which can hydrogen bond with neighboring water molecules. CH 3 F is polar but contains no O H , N H , or F H bonds to participate in hydrogen bonding. Therefore the strongest intermolecular forces CH 3 F experiences is dipole-dipole interactions. kamalska (mk23835) HW01 Quigley (104001) 2 He, H 2 , and C 2 H 6 are nonpolar and thus experiences only the weakest intermolecular forces, London forces....
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- Spring '08