011 10.0 points The DOMINANT intermolecular force that causes gaseous HCl molecules to attract one another is 1. None of these is dominant. 2. van der Waals. 3. ionic. 4. covalent. 5. dipole-dipole. correct Explanation: HCl would also possess van der Waals in- termolecular forces but, due to the small size, these would not be the dominant force. 012 10.0 points A unit cell of one of the new high- temperature superconductors is shown here.
kamalska (mk23835) – HW01 – Quigley – (104001) 4 Y (at outside corners of the cell) Ba (at inside corners of smaller cubes) O (at face centers of smaller cubes) Cu (at centers of smaller cubes). All atoms are on the surface of the unit cell except for the copper atoms and two of the oxygen atoms. What is its empirical formula? 1. YBa 2 Cu 4 O 7 2. Y 3 Ba 3 Cu 2 O 2 3. YBa 3 Cu 2 O 7 4. YBa 7 Cu 4 O 2 5. Y 8 Ba 8 Cu 3 O 12 6. Y 3 Ba 2 Cu 3 O 2 7. Y 2 Ba 2 CuO 3 8. YBa 7 Cu 2 O 3 9. Y 2 Ba 2 Cu 3 O 3 10. YBa 2 Cu 3 O 7 correct Explanation: Eight yttrium atoms lie on the corners, eight barium atoms lie on the edges, eight oxygen atoms lie on the faces and three cop- per atoms and two oxygen atoms lie inside the unit cell. Consider only the portion of the ions inside the unit cell. Y : 8 corners × 1 8 atom/corner = 1 Y Ba : 8 on edges × 1 4 atom/edge = 2 Ba Cu : 3 atoms within the cell = 3 Cu O : 10 on faces × 1 2 atom/face + 2 atoms within the cell = 7 O The empirical formula is YBa 2 Cu 3 O 7 013 10.0 points Arrange the molecules H 2 O , NH 3 , Ar , NaCl in order of expected increasing boiling points. 1. Ar, NH 3 , H 2 O, NaCl correct 2. NaCl, H 2 O, NH 3 , Ar 3. None of these 4. NH 3 , Ar, H 2 O, NaCl Explanation: London forces, dispersion forces, van der Waals or induced dipoles all describe the same intermolecular force. London forces are in- duced, short-lived, and very weak. Molecules and atoms can experience London forces be- cause they have electron clouds. London forces result from the distortion of the elec- tron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur be- tween polar covalent molecules due to charge separation. H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg- ative atoms – F, O or N only. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. The stronger the intermolecular forces, the more energy required to get the molecules to break away from one another, and the higher the boiling point. Ar – London Forces NH 3 – H-bonding H 2 O – H-bonding NaCl – Ion-Ion
kamalska (mk23835) – HW01 – Quigley – (104001) 5 014 10.0 points Consider two empty containers A and B whose volumes are 10 mL and 20 mL, respec- tively. You now put 1 mL of liquid H 2 O into each container and adjust the temperature of each container to 20 ◦ C. The gas pressure in container B is found to be 17 torr. The gas pressure in container A is 1. 8.5 torr.
- Fall '08
- Van der Waals force, London Forces