Key Multiple Choice (5 pts each) Identify the choice that best completes the statement or answers the question. CAREFULLY fill in the correct answer on the BUBBLE SHEET provided. Marks on this exam paper will NOT be graded, even if a mark here appears correct and the answer on the bubble sheet is incorrect. 1. Structural isomers are compounds that have a. the same molar masses, but different elemental composition. b. have identical structures, but contain different isotopes of the same elements. c. two or more resonance structures. d. the same elemental composition, but the atoms are linked in different ways. e. the same physical properties, but different chemical properties.. For which one of the following molecules do geometric (that is, cis/trans or E/Z) isomers exist? a. H C=CH b. BrHC=CHCl c. ClH CCH Br d. H CCH Cl e. H C=CCl. Which of the following molecules might be an alkyne? a. C H 6 b. C 4 H 10 c. C 5 H 10 d. C 6 H 10 e. C 6 H 1 4. What is the name of the following compound? a. 1,1,-trimethylpentane b.,4-dimethyloctane c. -methyl-4-propylbutane d.,5-dimethylhexane e.,4-dimethylhexane 1
5. How many isomers, both structural and geometric, exist for C 5 H 10? Consider non-cyclic isomers only. a. 5 b. 6 c. 7 d. 8 e. 9 6. Which one of the following hydrocarbons is aromatic? a. b. c. d. e. 7. Hydrogen bonding is present in all of the following molecular solids EXCEPT. a. H SO 4 b. NH c. PH d. HF e. H O H-bonding is only seen in NH, OH, FH, ClH systems. 8. As pure molecular solids, which of the following exhibits dipole-dipole intermolecular forces: HCl, Cl, SCl, and CCl 4? a. HCl only b. HCl and Cl c. HCl and SCl d. Cl and CCl 4 e. SCl and CCl 4 Cl and CCl 4 are non-polar therefore cannot interact in dipole-dipole way: they have no dipole. SCl is bent molecule due to tetrahedral electron pair geometry.
9. What intermolecular force or bond is primarily responsible for the solubility of carbon dioxide (CO ) in water? a. dipole/dipole force b. hydrogen bonding c. dipole/induced dipole force d. hydrogen bonding-dipole force e. ion-induced dipole force CO is non-polar, and H O is polar. A non-polar molecule cannot accept or donate a H-bond. 10. As pure molecular solids, which of the following exhibit only induced dipole/induced dipole forces: O, CH Cl, and SO? a. O only All the others are polar, and therefore have dipoles. HINT: b. CH Cl only go back and study Chap 10 where we learned about c. SO only molecular formulas, geometry, bond dipoles, molecular d. O and CH Cl dipoles, and all that. e. O and SO 11. Arrange Cl, ICl, and Br in order from lowest to highest boiling point. a. Cl < Br < ICl ICl is-polar, so it should have the highest BP. Smaller nonpolar compounds are gases, larger non-polar compounds b. Cl < ICl < Br c. ICl < Cl < Br d. Br < Cl < ICl are liquids or solids. This is due to the greater induceddipole/induced dipole interactions between molecules with e. Br < ICl < Cl large surface areas. 1. At its boiling point of 4.0 C, 6. kj of heat is required to vaporize.0 g of chlorine (Cl ). What is the molar enthalpy of vaporization of chlorine? a. 0.089 kj/mol b. 0.86 kj/mol 6.kJ 0.4kJ / mol c. 1.96 kj/mol 1 molcl d. 0.4 kj/mol.0 g Cl e. 19 kj/mol 70.90 g Cl 1. Which of the following phase transitions is/are exothermic? 1. liquid water evaporating into the gas phase.. the sublimation of solid carbon dioxide into the gas phase.. gaseous butane condensing into a liquid at its boiling point of 0.5 C. a. 1 only b. only c. only d. 1 and e. 1,, and endothermic 1 exothermic endothermic
14. Which of the following are valid reasons why vegetable oil has a greater viscosity than diethyl ether, CH OCH? (Typo - this is dimethyl ether! Diethyl ether is CH CH OCH CH ) 1. Unlike diethyl ether, oil molecules are not held together by hydrogen bonds.. Oil molecules have long chains that become entangled.. Intermolecular forces are greater for the larger oil molecules. a. 1 only b. only c. only d. 1 and e. and Diethyl ether cannot donate a H-bond it has no OH. Oil molecules are from 10-15 C atoms long: too short to become entangled, at least to the extent that polymer molecules do (100,00-1,000,000 C atoms long). 15. Arrange the three common unit cells in order from least dense to most dense packing. a. face-centered cubic < body-centered cubic < primitive cubic b. primitive cubic < body-centered cubic < face-centered cubic c. primitive cubic < face-centered cubic < body-centered cubic d. body-centered cubic < primitive cubic < face-centered cubic e. body-centered cubic < face-centered cubic < primitive cubic 16. Tungsten crystallizes in a body-centered cubic unit cell. If the radius of a tungsten atom is 0.17 nm, what is the length of an edge of the unit cell? a. 0.119 nm b. 0.194 nm c. 0.74 nm d. 0.16 nm e. 0.548 nm Way too involved a calculation for a short exam - at least the way Jk does it! Please do not memorize the geometric ratios. Nothing anywhere close to this complicated will appear on this exam. 4
17.For a primitive cubic unit cell, what percentage of the space in the cell is occupied by the atoms at the corners of the cell? a. 47% b. 5% vol of unit cell E r 8r c. 68% d. 74% 4r vol of one atom e. 87% 4r Fraction 0.5 8r 6 18. Which of the following compounds is expected to have the strongest ionic bonds? a. RbI b. RbF c. NaI d. CsBr e. LiF The smallest ions are closer together, and since the attractive force is inversely dependent on the square of the separation distance, these have the strongest attractive forces. 19. The lattice energy of KF is 81 kj/mol. This energy corresponds to which reaction below? a. K(s) + 1/ F (g) KF(s) b. K(g) + F(g) KF(s) c. K(g) + F(g) KF(s) d. K + (g) + F (g) KF(s) e. K + (aq) + F (aq) KF(s) The lattice energy is energy from forming the crystal lattice from gaseous ions. 0. Which statement concerning the phase diagram below is INCORRECT? a. Only the solid phase exists at point A. b. At point D, the triple point, all three phases (gas, liquid, and solid) are in equilibrium. c. Moving from point A to B results in a phase transition from solid to liquid. d. At point C, the solid and liquid phases are in equilibrium. e. Only the liquid phase exists at point B. The liquid and GAS are in equilibrium at C. 5
1. If 55 g of ethanol (C H 5 OH) is added to 645 g of water, what is the molality of the ethanol? a. 0.550 m b. 7.71 m 1mol Ethanol 55 g Ethanol c. 11.9 m mol solute 46.07g Ethanol d. 1.7 m m kg solvent 1kg H O e. 55.0 m 645gHO 1000gHO m11.94m. Which of the following statements is/are CORRECT? 1. Solubility is defined as the concentration of solute in equilibrium with undissolved solute in a saturated solution.. If two liquids mix to an appreciable extent to form a solution, they are miscible.. If two liquids mix completely in any proportion to form a solution, the resulting solution is supersaturated. Yes Must mix in ALL proportions to be miscible -like water and ethanol THIS is miscible a. 1 only b. only c. only d. 1 and e. and. In which solvent should Na + have the most negative enthalpy of solvation? a. CCl 4 b. H O This would be the most exothermic c. C 6 H 6 due to the strong ion-dipole d. CS interactions. e. C 6 H 14 4. Which action(s) will increase the equilibrium concentration of a non-reacting gas in water? 1. decreasing the temperature of the water Yes. increasing the volume of water. decreasing the pressure of the gas above the liquid No - gas will just dissolve more a. 1 only b. only c. only d. 1 and e. 1,, and No -this will decrease the concentration Henry s Law 6
5. Ideally, colligative properties depend only on the a. concentration of solute particles in a solution. b. molar masses of the solute particles in a solution. c. density of a solution. d. hydrated radii of the molecules or ions dissolved in a solution. e. partial pressure of the gases above the surface of a solution. 6. The vapor pressure of pure water at 55 C is 118 mm Hg. What is the equilibrium vapor pressure of water above a mixture of 77.0 g ethanol (CH CH OH, molar mass = 46.07 g/mol) and.0 g water? a..7 mm Hg 0 mol H b. 4.6 mm Hg O 0 PH O XHOPHO PHO c. 49.0 mm Hg mol H O moletoh d. 57. mm Hg 1mol H O e. 60.8 mm Hg.0gHO 1.78molHO 18.0gHO 1mol EtOH 77.0 getoh 1.67 moletoh 46.0gEtOH 1.78 0 PHO PHO60.8mmHg 1.78 1.67 7. Which of the following aqueous solutions should have the lowest freezing point? a. pure H O no solute b. 1 m MgBr i = c. 1 m RbI i = d. 1 m NH i = 1 e. 1 m C 6 H 1 O 6 i = 1 7
PART II 8. (9 pts) Draw formulas for FOUR alkene structural isomers having a molecular formula of C7H14. Provide correct systematic (I.U.P.A.C.) names for TWO. H C CH H C CH H C CH 1-heptene -heptene -heptene H C CH H C CH H C CH CH -methyl-1-hexene CH -methyl--hexebe CH -methyl--hexene H C H C CH CH CH CH 5-methyl--hexene 5-methyl-1-hexene (and more ) 9. (9 pts) Platinum (Pt) crystallizes in a face-centered cubic unit cell. In addition, platinum has an atomic radius of 19 pm. Calculate the density in g/cm of platinum. (Please read the directions above and on p. 1.) d = mass/volume, which here is the fcc unit cell pythagorean 4r x 16r x x x r 19 pm 9. pm vol of cube x 7 6.077 x10 pm 7 6.077 x10 10 cm 1m m 1 10 pm 6.077 x10 cm d d m v 4 atoms Pt 1. g / cm 1mol Pt 6.0x 10 atoms Pt 6.077 x10 cm 195.08 g Pt 1mol Pt 1.956 x10 1 g Pt 6.077 x10 cm 8
0. (9 pts) The boiling point of water is 100.000 C at 1 atmosphere. In a laboratory experiment, students synthesized a new compound and found that when 11.80 grams of the compound were dissolved in 70.0 grams of water, the solution began to boil at 100.14 C. The compound was also found to be nonvolatile and a non-electrolyte. Calculate the molecular weight of this compound. (Please read the directions above and on p. 1.) T b m ik m b T b ik b m 0.4 m 0.4 mol x kgsolvent 0.70 kg x 0.0659 mol molar mass 100.14C 100.000C 1 0.51C / m g 11.80 g 180. mol 0.0659 mol g / mol 9