CDO AP Chemistry Unit 7 Review

CDO AP Chemistry Unit 7 Review MULTIPLE CHOICE REVIEW 1. Surface tension in a liquid is due to the fact that a) surface molecules are pulled toward the interior b) liquids tend toward lowest energy c) PE is increased for molecules at the surface d) interior molecules are attracted in all directions e) all of the above 2. In which one of the following will dipole-dipole attractions play the most significant role as the intermolecular attraction? a) HCl d) H2O b) NaCl e) NH3 c) Kr 3. With which type of substances do London dispersion forces play the most significant role? a) polar molecules d) non-polar molecules b) metals e) network compounds c) ionic compounds 4. The heat of vaporization of H2S, at its boiling point ( 61 C) is 18.8 kj/mol. What mass of H2S can be vaporized (at its boiling point) with 100 kj of energy? 61 61 a) 100 x d) 18.8 x 18.8 34.1 18. 8 34.1 b) 34.1 x e) 100 x 100 18.8 c) 61 x 18.8 x 100 x 34.1 5. Which one of the following substances exhibits the strongest intermolecular forces of attraction? a) CH4 d) CH3OH b) C2H6 e) CH3Cl c) C3H8 6. For which substance would you predict the highest heat of vaporization? a) F2 b) H2O c) HF d) NaCl e) Br2 7. Which of the following will change the equilibrium vapor pressure of a liquid? I. Heat up or cool down the liquid II. Increase the Volume of the container III. Change the pressure above the liquid a) I only d) I and III only b) I and II only e) II and III only

page 2 c) I, II, and III 8. Which of the following statements describes a substance above its critical point? a) the substance can be liquefied b) the vapor and liquid phase become indistinguishable c) the substance experiences no intermolecular interactions d) there is a distinct phase boundary between the liquid and vapor e) all of the above 9. At what temperature will the liquid (whose vapor pressure is shown below) boil if the air pressure is reduced to 380 mmhg? a) 30 C b) 50 C c) 70 C d) 100 C e) the liquid will not boil at this pressure 10. Which one of the following is linked with the correct intermolecular force of attraction? a) NH3... dipole-dipole b) AlH3... London dispersion forces c) H2... hydrogen bonding d) C2H4... covalent bonding e) HCl... ionic 11. The vapor pressure graph of an unknown liquid is shown below. Which of the following statements about this liquid is/are true? I. This liquid has weaker IMF s than water. II. The liquid s normal boiling point is around 75 C. III. The liquid boils at room temperature when the pressure is dropped to about 0.25 atm. a) II and III only d) I only b) II only e) I, II, and III c) I and III

page 3 12. How much energy does it require to melt 25.0 g benzene, C6H6? The heat of fusion of benzene is 2.37 kj/mol. [molar mass = 78.0 g/mol) a) 8.25 kj d) 0.759 kj b) 59.3 kj e) none of these c) 4625 kj 13. What type of solid(s) can contain covalent bonds? a) molecular d) network b) metallic e) all but b c) ionic 14. Which type of solid generally has the highest melting point? a) metallic c) molecular b) ionic d) network 15. Which substance below exhibits the weakest IMFs? a) IF3 b) SO2 c) CO2 d) SiO2 e) PH3 16. During the condensing of a liquid, the kinetic energy and the potential energy. a) stays the same, increases b) increases, decreases c) increases, increases d) decreases, stays the same e) stays the same, decreases 17. The phase diagram of a substance is given below. What occurs when the substance is heated from 100 C to 120 C at 3 atm pressure? a) it melts d) it freezes b) it sublimes e) no phase c) it boils change occurs

page 4 18. A typical phase diagram for a substance is given below. At what point on the diagram do solid and liquid exist at equilibrium? a) A b) B c) C d) D e) E 19. Which one of the following as solids has a crystal structure containing discrete (separate) molecules? a) potassium d) carborundum, SiC b) glass e) hydrogen c) quartz 20. The heat of sublimation of a compound equals a) heat of fusion plus heat of vaporization b) heat of ionization plus heat of crystallization c) heat of vaporization minus heat of fusion d) heat of vaporization plus heat of crystallization e) heat of crystallization plus heat of vaporization 21. The normal boiling point of a liquid a) is 100 C at 1 atm pressure. b) is the temperature at which the vapor pressure is 1 atm. c) is the temperature at which liquid and vapor are in equilibrium. d) is the temperature at which the vapor pressure equals the external pressure. e) is the temperature at which there is a continuous formation of gaseous bubbles in the liquid. 22. The vapor pressure of a liquid increases with an increase of temperature. Which of the following best explains this increase? a) The average kinetic energy of molecules is greater, thus more molecules can enter the gaseous state. b) The number of gaseous molecules above the liquid remains constant but these molecules have greater average kinetic energy. c) the faster moving molecules in the liquid exert a greater pressure. d) All the molecules have greater kinetic energies. e) The intermolecular forces between the molecules becomes less at higher temperatures. 23. Which of the following indicates very strong intermolecular forces of attraction in a liquid? a) A very low boiling point. b) A very low critical temperature. c) A very low heat of vaporization. d) A very low vapor pressure. e) A very low surface tension.

page 5 24. The compounds Br2 and ICl have almost identical molecular weights, yet ICl boils at 97 C and Br2 boils at 59 C. The best explanation for the difference is a) ICl is an ionic compound and Br2 is covalent. b) ICl is a nonpolar molecule and Br2 is polar. c) ICl has a longer bond than that in Br2. d) ICl has a measurable dipole moment (is polar) and Br2 does not (is nonpolar). e) ICl has a stronger bond than that in Br2. 25. In some compounds the hydrogen atom is covalently bonded to one atom and simultaneously attracted to another atom in another molecule by an electrostatic interaction. This interaction can occur when hydrogen is bonded to a) Cl b) Si c) N d) C e) Br 26. Which of the following compounds shows an abnormal boiling point due to hydrogen bonding? a) CH3NH2 d) CH3Cl b) CH3OCH3 e) HCl c) CH3SH 27. Which of the following has the lowest boiling point? a) H2O d) H2Te b) H2S e) NH3 c) H2Se 28. Which of the following would be expected to have the highest heat of vaporization? a) H2O c) HF b) NH3 d) all three are the same 29. Which element is considered a covalent/network solid? a) Cr b) O c) Xe d) B e) Na 30. Which one of the following compounds has intermolecular forces different than the others? a) quartz, SiO2 d) C(graphite) b) C(diamond) e) silicon carbide, SiC c) carbon dioxide, CO2 32. The maximum contamination level of arsenic ion in a water system is 0.050 parts per million. If the arsenic is present as AsCl 3, how many grams of arsenic chloride could be present in a system that contains 8.2 x 10 5 Liters? a) 0.55 g d) 62 g b) 7.3 g e) 98 g c) 41 g

page 6 33. A student prepared a solution containing 0.30 mol solute and 1.00 mole solvent. The mole fraction of solvent is a) 1.30 d) 0.30 b) 1.00 e) 0.23 c) 0.77 34. Which measure of concentration is most appropriate for the calculation of the vapor pressure of a solution? a) mol fraction d) weight % b) molarity e) ppm c) molality 35. A chemist knows the empirical formula of a new compound but not the molecular formula. What must be determined experimentally so that the molecular formula can be determined? a) density d) melting point b) viscosity e) molar mass c) % composition 36. A volumetric flask is necessary for the preparation of which one of the following concentration measurements? a) molality d) molarity b) X e) ppm c) mass % 37. If the pressure of a gas over a liquid increases, the amount of gas dissolved in the liquid will a) increase b) decrease c) remain the same d) have a higher vapor pressure e) depends on the polarity of the gas 38. Which of the following solutions would have the lowest vapor pressure? a) 1 m glucose (C 6 H 12 O 6 ) b) 1 m MgCl 2 d) 1 m NaBr c) 1 m NaNO 3 e) pure H 2 O 39. What is the primary energetic factor in the lack of miscibility between CCl 4 (l) and water? a) the strength of intermolecular forces between CCl 4 molecules b) the strength of intermolecular forces between H 2 O molecules c) the charge on the C atom in CCl 4 d) the difference between the molecular weights of the molecules e) the electronegativity difference between carbon and chlorine 40. Which of the following would have a boiling point closes to that of 1 m NaCl? a) 1 m sucrose (C 12 H 22 O 11 ) b) pure H 2 O d) 0.5 m CH 3 OH c) 1 m MgCl 2 e) 1 m NH 4 NO 3 41. Which of the following would have the highest freezing point? a) 1 m glucose (C 6 H 12 O 6 ) b) 1 m MgCl 2 d) 1 m (NH 4 ) 2 SO 4 c) 1 m NaNO 3 e) pure H 2 O

page 7 42. Concentrated salt solutions have boiling points lower than those calculated using the equation, T b = K b m. i Which of the following is a reasonable explanation of this observation? a) Positive ions repel each other more at high concentration. b) Ions of opposite charge will tend to stay paired instead of breaking up. c) The water molecules will have a greater attraction for each other. d) Concentrated solutions really have small particles of non-dissolved salt, thus lowering the molality. e) The difference between the crystal lattice energy and the heat of hydration must be taken into consideration 43. Which substance in the solid phase has the strongest intermolecular forces? a. Cl 2 b. Na c. CO 2 d. C (d) e. C 5 H 12 44. A given liquid would have what combination of properties? Vapor Pressure Heat of Vaporization a. high high high b. low low low c. high low low d. low low high e. high high low Attractive forces 45. What gas is most soluble in water? a. Carbon dioxide b. Ammonia c. Methane d. Oxygen e. Nitrogen 46. Which compound would be expected to be most soluble in water? a. C 6 H 6 b. C 2 H 4 c. (C 2 H 5 ) 2 O d. 1.0 m CHCl 3 e. (CH 3 ) 2 NH 47. A solute dissolved in benzene lowers the freezing point of the solution to a temperature that is lower than the freezing point of pure benzene. The amount of change in freezing point depends on a. the number of particles formed by the solute when dissolved b. the molar mass of the solvent c. the freezing point of the solute d. the atmospheric pressure e. the temperature of the solvent 48. Consider two solutions: a 0.25 molal solution of Fe(NO 3 ) 3 and a 0.50 molal solution of NaCl. Which statement about the solutions is correct? a. The sodium chloride has a lower freezing point because the salt concentration is greater. b. The iron (III) nitrate solution has a higher boiling point because the total ion concentration is greater. c. Both solutions freeze at approximately the same negative Celcius temperature because they have equal ion concentrations d. The iron (III) nitrate solution has a higher vapor pressure because the total ion concentration is greater. e. The iron (III) nitrate freezes at a higher temperature because it is more acidic.

page 8 49. Which aqueous solution will boil at the highest temperature? a. 0.5 m C 6 H 12 O 6 b. 1.0 m C 2 H 5 OH c. 1.25 m NaCl d. 1.0 m CaCl 2 e. 0.5 m AlCl 3 FREE RESPONSE REVIEW 1. The boiling points of the following compounds increase in the order in which they are listed below: CH 4 < H 2 S < NH 3 Discuss the theoretical considerations involved and use them to account for this order? Each of these compounds have different polarities and IMF. CH4 is non polar and only has London dispersion forces, the weakest force of attraction so would have the lowest bp. H2S is polar and had dipole dipole interactions as its predominant force of attraction and ammonia is polar and has hydrogen bonds is the strongest imf and causes it to have the highest bp 2. Using principles of chemical bonding and/or intermolecular forces, explain each of the following. (a) Xenon has a higher boiling point than neon has. Xe is a larger than Ne so it is more polarizable, although they both only have London dipersion forces the polarizability of Xe increases its bp (b) Solid copper is an excellent conductor of electricity, but solid copper chloride is not. Solid Cu has metallic bonds with a sea of delocalized electrons which allows for easy conduction of electricity, Copper Chloride in its solid state the ions are unable to move so electricity cannot flow. In order for an ionic compound to conduct electricity it must be molten or dissolved in water (c) SiO 2 melts at a very high temperature, while CO 2 is a gas at room temperature, even though Si and C are in the same chemical family. SiO2 is held together by network covalent bonds in order for it to melt a covalent bond must be broken which requires a great deal of energy, CO2 is a non polar molecule held together by London dispersion forces, which is a very weak force of attraction which allows the CO2 molecules to be far apart and be in the gaseous phase at room temp. 3. The melting points of the alkali metals decrease from Li to Cs. In contrast, the melting points of the halogens increase from F 2 to I 2. (a) Using bonding principles, account for the decrease in the melting points of the alkali metals. The melting points decrease because at the alkali metals get larger the attraction between the delocalized electrons become weaker since the electrons become more dispersed. The weaker attraction makes the mp decrease. (b) Using bonding principles, account for the decrease in the melting points of the halogens. The melting points of the halogens increases down the group. This is because all of the halogens are diatomic molecules, all non polar and all have weak London dispersion attractions. This weak force of attraction increases with the size of the molecules, as the size increase the LDF increases due to an increase in polarizability

page 9 (c) What is the expected trend in the melting points of the compounds LiF, NaCl, KBr, and CsI? Explain this trend using bonding principles. The melting point would decrease as the strength of the ionic bond decreases. 2 things affect the strength of the ionic bond, size and charge. All of these have the same quantity of positive and negative charge which means the factor that would account for the trend in mp is size. As you go down each group the atomic size increases, this would cause the ionic bond to be weaker since the atoms are larger. The mp would be ordered as CsI < KBr < NaCl < LiF 4. Explain each of the following in terms of atomic and molecular structures and/or intermolecular forces. (a) Solid K conducts an electric current, whereas solid KNO 3 does not. Solid K has metallic bonds with a sea of delocalized electrons which allows for easy conduction of electricity, Potassium nitrate in its solid state the ions are unable to move so electricity cannot flow. In order for an ionic compound to conduct electricity it must be molten or dissolved in water (b) SbCl 3 has measurable dipole moment, whereas SbCl 5 does not. SbCl 3 is a polar molecule with polar bonds so has a dipole moment and SbCl 5 is a non polar molecule so it doesn t have a dipole (c) The normal boiling point of CCl 4 is 77ºC, whereas that of CBr 4 is 190ºC. Both are non polar molecule which only have London dispersion forces, CBr 4 is a much larger molecule so is more polarizable so the strength of the dispersion forces are greater giving a higher bp (d) NaI(s) is very soluble in water, whereas I 2 (s) has a solubility of only 0.03 gram per 100 grams of water. NaI is an ionic compound (polar) which can form ion-dipole interaction with water, Iodine is non polar diatomic molecule and the water would be more attracted to itself and less attracted to the iodine. 5. 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. (a) 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). NH 3 is a polar molecule which contains H bonding and CH 4 is a non polar molecule with dispersion forces. Ammonia Hbonding is a stronger IMF and causes it to have a much higher bp because it would take more energy to move the molecules further apart. (b) At 25 C and 1.0 atm, ethane (C 2 H 6 ) is a gas and hexane (C 6 H 14 ) is a liquid. Both are nonpolar, however hexane is a much larger molecule. Hexane is than more polarizable so the dispersion IMF is stronger causing the molecule to be closer together, and be in the liquid phase. (c) Si melts at a much higher temperature (1,410 C) than Cl 2 (-101 C). Si contains network covalent bonds where Cl2 is held together by dispersion IMF In order to melt the Si the covalent bonds must be broken which requires a lot of energy to break so it can melt. The force of attraction in Cl2 is fairly weak in comparison and is NOT a bond causing it take less energy to melt (d) MgO melts at a much higher temperature (2,852 C) than NaF (993 C). MgO has a higher charge than NaCl so the ionic bond is stronger to a higher columbic attraction, causing more energy to melt the MgO

page 10 6. Use appropriate chemical principles to account for each of the following observations. In each part, your response must include specific information about both substances. (a) At 25 C and 1 atm, F2 is a gas whereas I2 is a solid. F2 is smaller the I2 so I2 is more polarizable creating a stronger dispersion IMF making the molecules so close together they are a solid (b) The melting point of NaF is 993 C, whereas the melting point of CsCl is 645. NaF occurs between to relatively small atoms where Cs in CsCl is large in comparison making the ionic bond weaker due to a smaller columbic attraction, so less energy is require to melt the compounds (c) Ammonia, NH3, is very soluble in water, whereas phosphine, PH3, is only moderately soluble in water. Both are polar which is explains why both are soluble in water, however NH3 can Hbond with water where PH3 cannon, making ammonia more soluble the PH3 Compound Name Compound Formula Propane CH 3 CH 2 CH 3 19.0 Propanone CH 3 COCH 3 32.0 1-propanol CH 3 CH 2 CH 2 OH 47.3 H vap (kj mol -1 ) 7. Using the information in the table above, answer the following question about the organic compounds. For each pair of compounds below, explain why they do not have the same value for their standard heat of vaporization, H vap. (You must include specific information about both compounds in each pair.) (i) Propane and propanone (ii) Propanone and 1-propanol i) propane, 26 electrons, molar mass = 44 propanone, 32 electrons, molar mass = 58 higher # electrons means larger van der Waal forces, larger molar mass means a slower molecule, the oxygen creates a polar molecule and dipole dipole interactions (ii) 1-propanol has an OH which creates a site for hydrogen bonding with other OH on adjacent molecules increasing intermolecular forces that must be overcome in order to vaporize the liquid.

page 11 8. Use principles of atomic structure, bonding and/or intermolecular forces to respond to each of the following. Your responses must include specific information about all substances referred to in each question. (a) At a pressure of 1 atm, the boiling point of NH3(l) is 240 K, whereas the boiling point of NF3(l) is 144 K. (i) Identify the intermolecular forces(s) in each substance. (ii) Account for the difference in the boiling points of the substances. (b) The melting point of KCl(s) is 776 C, whereas the melting point of NaCl(s) is 801 C. (i) Identify the type of bonding in each substance. (ii) Account for the difference in the melting points of the substances. (a) (i) force NH3 NF3 London dispersion polar attraction hydrogen bonding ionic attraction + + + + + - - - (ii) the ability of ammonia to create intermolecular hydrogen bonds, leads to higher amount of energy to separate the molecules by boiling them. (b) (i) both compounds have ionic bonding (ii) the sodium ion in NaCl is a smaller size than the corresponding potassium ion in KCl. This smaller size creates greater Columbic attraction in the NaCl, making it harder to melt. 9. Give a scientific explanation for the following observations. Use equations or diagrams if they are relevant. (a) It takes longer to cook an egg until it is hard-boiled in Denver (altitude 1 mile above sea level) than it does in New York City (near sea level). Water boils at a lower temperature in Denver than in NYC because the atmospheric pressure is less at high altitudes. At a lower temperature, the cooking process is slower, so the time to prepare a hard-boiled egg is longer. (b) Perspiring is a mechanism for cooling the body. Vaporization or evaporation of sweat from the skin is an endothermic process and takes heat from the body and so cool the skin. (c) C (graphite) is used as a lubricant, whereas C (diamond) is used as an abrasive. Although both network covalent structure the network covalent structure in graphite is held together by LDF where the diamond is a complete network covalent solid. It is easy to disrupt the LDF so graphite can be used as a lubricant 10. The bonding of metals in the can be described as an electron-sea model. (a) Draw a diagram to illustrate a small segment of a metal and its electron sea.

page 12 (b) Typical metal properties are listed as: (i) Ductile can be made into wires (ii) Lustrous reflecting light and having shine (iii) Malleable can be made into thin sheets (iv) Conducting have good electrical conductivity. Describe how each of these four properties can be explained on the basis of the electron sea model of metals. i) electrons act like flexible glue holding them nuclei together ii) the electron sea will reflect light of all wavelength are not restricted to a particular nuclei iii) electrons act like flexible glue holding them nuclei together iv) the electrons being delocalized allow for free flow of electrical current (c) An engineer has formed a company to promote the use of sodium wires for high voltage electricity transmission line since sodium had three times the electrical conductivity per gram compared to copper wires. Explain why sodium metal is such a good conductor, using the atomic properties of sodium and the electron sea model. the electrons being delocalized allow for free flow of electrical current, although the sodium would be a bad choice due to the reactivity 11. The states of solids can be described as belonging to the following four types: (1) ionic (3) covalent network (2) metallic (4) molecular For each of these types of solids, indicate the kinds of particles that occupy the lattice points and identify forces among these particles. How could each type of solid be identified in the laboratory? 1) metals and non metals held together by electrostatic attraction could be identified by solublity in water and by its ability to conduct electricity in the molten phase 2) metal held together by metallic bonding could be able to be identified by their conductivity in the solid state 3) Si compounds, C held together by covalent bonds very high melting points brittle weak conductors in the solid phase 4) non metals covalent bonds relatively low melting points

CDO AP Chemistry Unit 7 Review

CDO AP Chemistry Christman Unit 7 2014