Advanced Chemistry Liquid & Solids Test

Transcription

1 Advanced Chemistry Liquid & Solids Test Name: Multiple Choice 1) Which one of the following statements about liquids and solids is generally false? a) The rate of diffusion is lower in solids b) The density of solids is higher c) The compressibility of liquids is higher d) Liquids have higher vapor pressures e) The heat of vaporization is less than the heat of fusion 2) The boiling points of the halogens increase from F 2 to I 2. What type of intermolecular forces are responsible for this trend? a) permanent dipole b) hydrogen bonding c) ion-ion attraction d) London dispersion forces e) ion-dipole attraction 3) Which of the following has the lowest boiling point? a) CF 4 b) HF c) Cu d) KI e) SiF 4 4) On a relative basis, the weaker the intermolecular forces in a substance, a) the greater the heat of vaporization b) the more it deviates from the ideal gas behavior c) the greater its vapor pressure at a particular temperature d) the higher its melting point 5) Which species below would you expect to have the lowest hydrogen bonding? a) NH 3 b) H 2 O c) HF d) CH 4 e) all the same 6. Which of the following statements is true about liquids? a) Droplet formation occurs because of the higher stability associated with increased surface area. b) Substances that can form hydrogen bonds will display lower melting points than predicted from periodic trends c) London dispersion forces arise from a distortion of the electron clouds within a molecule or atom d) Liquids rise within a capillary tube because the small size lowers the effective atmospheric pressure over the surface of the liquid. e) The boiling point of a solution is dependent solely on the atmospheric pressure over the solution. 7. In which of the following groups of substances would dispersion forces be the only significant factors in determining boiling points? I. Cl 2 II. HF III. Ne IV. KNO 2 V. CCl 4 a) I, III, V b) I, II, III c) II, IV d) II, V e) III, IV, V 8. A certain solid substance that is very hard, has a high melting point, and is a nonconductor unless melted is most likely to be: a) I 2 b) NaCl c) CO 2 d) H 2 O e) Cu 9. The best explanation for the fact that diamond is extremely hard is that diamond crystals a) are made up of atoms that are intrinsically hard because of their electronic structures b) consist of positive and negative ions that are strongly attracted to each other. c) are giant molecules in which each atom forms strong covalent bonds with all of its neighboring atoms d) are formed under extreme conditions of temperature and pressure. e) contain orbitals or bands of delocalized electrons that belong not to single atoms but to each crystal as a whole. 10. The boiling points of the elements helium, neon, argon, krypton, and xenon increase in that order. Which of the following statements accounts for that increase? a) The London dispersion forces increase b) The hydrogen bonding increases. c) The dipole-dipole forces increases d) The chemical reactivity increases e) The number of nearest neighbors increases.

2 11. Which of the following describes the changes in forces of attraction that occur as H 2 O changes phase from a liquid to a vapor? a) H-O bonds break as H-H and O-O bonds form b) Hydrogen bonds between H 2 O molecules are broken c) Covalent bonds between H 2 O molecules are broken d) Ionic bonds between H + ions and OH - ions are broken e) Covalent bonds between H + ions and H 2 O molecules become more effective. 13. Of the following pure substances, which has the highest melting point? a) S 8 b) I 2 c) SiO 2 d) SO 2 C 6 H 6 Refer to the Lewis Dot Structures below for questions Which of the above molecules has/have hydrogen bonding as its/their strongest intermolecular force? a. A and B b. A, B, and D c. C Only d. A and D 15. Of the structures listed above, which would have the highest vapor pressure? a. A b. B c. C d. D 16. Rank the boiling points of the above structures from lowest to highest. a. C, B, A = D b. A = D, B, C c. C, B, A, D d. C, B, D, A Refer to the following statement for questions 17 and 18. The substances that comprise the glassware in our laboratory are mainly SiO 2 and B 2 O When placed into a graduated cylinder composed of glass, bromine forms a meniscus which faces upward (has a higher volume in the middle than on the sides). This is a primary example of forces. a. adhesive b. cohesive c. dipole-dipole d. ion-dipole 18. Which of the below substances will exhibit the greatest capillary action within a narrow tube of the glassware? a. C 8 H 18 b. C 4 H 10 c. C 5 H 12 d. C 7 H Which of the following statements best explains why magnesium oxide has a greater melting point than sodium chloride? a. The London dispersion forces in magnesium oxide are greater than in sodium chloride. b. The ions in sodium chloride are larger than they are in magnesium oxide, leading to greater electrostatic attraction. c. Calcium oxide is a network covalent solid and held together with bonds, while sodium chloride has only ionic bonding and attraction. d. The ions in calcium oxide have larger charges than in sodium chloride, leading to great electrostatic attraction.

3 Refer to the below Lewis Dot Structures for questions 20 and Which of the below statements best describes the relationship between the boiling points of the two substances? (C 12 H 26 = o C and H 2 O 2 = o C) a. C 12 H 26 has a higher boiling point because its molar mass leads to more polarizability and attraction than H 2 O 2. b. C 12 H 26 has a higher boiling point because it has London dispersion forces, which is a stronger intermolecular force than H-Bonding. c. C 12 H 26 has a higher boiling point because it has a higher vapor pressure than H 2 O 2 based on the attractive forces at the liquid s surface. d. C 12 H 26 has a higher boiling point because it has a higher viscosity than H 2 O 2, making it more difficult to disrupt molecular attraction. 21. Between the two above substances, which would be more readily soluble with ethane (C 2 H 6 )? a. H 2 O 2 because they have much more similar molar masses. b. C 12 H 26 because it has a larger molar mass than both H 2 O 2 and C 2 H 6. c. H 2 O 2 because it has the stronger intermolecular forces (H-Bonding). d. C 12 H 26 because it has the same polarity as C 2 H 6. Refer to the below set of figures for questions 22 and In Figure D, the dipole-dipole forces are shown as: a. the solid line between two carbons. b. the double solid line between a carbon and an oxygen. c. the bond that exists between a carbon and a hydrogen. d. the dotted line that exists between a carbon and an oxygen. 23. Which of the above molecules show hydrogen bonding? a. A Only b. A and C c. C Only d. A, B, and C 24. Which of the following is expected to be malleable and have luster? a. Au b. CaCl 2 c. Si d. C 4 H 9 OH

4 Essay: Account for each of the following observations about pairs of substances. In your answers, use appropriate principles of chemical bonding and/or intermolecular forces. In each part, your answer must include references to both substances. 1) At 25.0 C and 1.0 atm, ethane is a gas and hexane is a liquid. 2) The melting point of NaF is 993 C whereas the melting point of CsCl is 645 C. 3) Even though NH 3 and CH 4 have similar molecular masses, NH 3 has a much higher normal boiling point (-33 C) than CH 4 (-164 C). 4) The melting point of KCl(s) is 776 C, whereas the melting point of NaCl(s) is 801 C. 5) The boiling point of Cl 2 is lower than the boiling point of Br 2. 6) Si melts at a much higher temperature (1,410 C) than Cl 2 (-101 C).

5 7) A ml sample of C 9 H 19 OH and a ml sample of C 5 H 12 are in separate flasks at 1 atm and 25 o C. a. Provide a molecular picture for each flask that clearly depicts the differences in vapor pressure between the liquid substances. The picture should include the liquids in a sealed container and show gas molecules present on a molecular level. b. Explain the above molecular pictures. Address why the vapor pressures vary for the two substances. Be thorough in your response. 8) A 2.0 mol sample of potassium chloride are used to make 1.0 L of a 2.0 M solution of potassium chloride. The solvent for this solution is water. a. Provide a molecular picture that clearly depicts the ion-dipole interactions for both the potassium ions and the chloride ions. Label the ion-dipole interactions using a dotted line to show the molecular attractions. (Assume 1 mol of an ion = 1 particle of the ion in the picture. Be sure that your picture abides by the Law of Conservation of Matter.) b. Discuss and explain how the strength of the intermolecular attractions would play a role had the solute been calcium oxide, an insoluble solid, as opposed to potassium chloride. Draw upon evidence to support your claims.

6 9) A flask contains a sample of a gas whose strongest intermolecular forces are dipole-dipole interactions. a. The gas is cooled until it has undergone a complete phase change to a liquid. Draw a before AND after molecular picture showing the differences between the intermolecular forces in the gas and liquid state. Use dotted lines to represent the intermolecular attractions between molecules. b. How would the strength of the intermolecular forces have been impacted if a gas with a lower molar mass had been used? Discuss how and why this impacts the strength of the intermolecular forces and what this would do to the temperature at which the gas condenses. 10) A chromatography experiment was conducted. The results are posted here: a. The solutes used were C 18 H 37 OH and C 20 H 42. If the solvent used was water, identify A and B. Justify your answer in terms of both compounds and their relative intermolecular forces. b. How could the retention factor of solute B be determined? Show and explain the setup for this calculation. c. If hexane were used as the solvent instead of water, how would the results be different? Explain.