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Unformatted text preview: Chem101 (Bontems, Fall 2009, TTH) Exam 4 Name: ____Key___________________ Multiple Choice – In the blank, write the letter of the best answer. (3 pts. ea.) 1.C________ The formal charge in the structure shown are a. all are zero b. S = +1, C = ‐1 c. S = +2, C = ‐2 d. e. S = ‐1, C = +1 S = ‐2, C = +2 2.B________The bond angle marked in the following molecule is about _________. H
H H N C S
H H a. b. o 90 109o c. d. 120o 180o 3.C________Which of the following has the bonds correctly arranged in order of increasing polarity? a. Li‐F < C‐F < O‐F c. O‐F < C‐F < Li‐F b. C‐F < Li‐F < O‐F d. none of these 4. D_______ The electron cluster geometry of AsF6‐ ion is octahedral. The hybrid orbitals used by the As atom for bonding are ______. a. sp2 d. sp3d2 e. cannot be determined b. sp3 5 c. sp 5. B_______Which of the following substances is least likely to dissolve in water? a. HF c. CH3CH2CH2OH b. CS2 (S=C=S) d. NaBr 6. B Which of the following substances would most likely have the lowest viscosity? O a. HOCH2CH2CH2CH2OH c. CH3CH2 C CH2CH3 H
CH3CH2 N CH2CH3 b. CH3CH2CH2CH2CH3 d. 7. B_______Which of the molecules in Q6 above will have the highest vapor pressure? 2 8. Consider the following molecules and answer the questions below. (3 pts each) a)
f) Which has higher boiling point, A or B? A Which has the lower boiling point, C or D? C Which has a higher vapor pressure, E or F? F Which molecules (A‐F) would probably dissolve in water? E,F Which compounds above have LDF only? A, B, C, D Which compound would have the highest viscosity? E 9. Consider the vapor pressure curves below. (6 pts) a. Which compound has the lowest boiling point? A b. Estimate the normal boiling point of sample B. Show how you decided. Approx 68° c. Which compound is most likely to have hydrogen bonding as its intermolecular force? C 10. Define viscosity and surface tension and explain how these are affected by IMFs. (6 pts) Viscosity is the resistance to flow. Stronger IMFs cause higher viscosity. Surface Tension is the E required to increase the surface area of a liquid. Stronger IMFs give higher surface tension. 3 11. Consider the phase diagram shown below. (7 pts) a. Label the phases. b. Estimate the normal freezing point and indicate how you determined this value. Approx 10°C c. When a sample of this compound is heated from 0°C to 20°C at a constant pressure of 300 mmHg, what transition occurs? (Give the correct technical term.) Sublimation d. When the pressure is decreased from 500 to 200 at a constant temperature of 20°C, what transition occurs? (Give the correct technical term.) vaporization 12. Describe the intermolecular forces that must be overcome to convert each of the following from a liquid into a gas. Define each force you list. (8 pts) a) CF4 LDF only LDF is the attraction between temporary δ+ and δ‐ caused by shifting electron clouds. b) NH3 H‐bonding H‐bonding is the very strong attraction between very polar N‐H, O‐H or H‐F. These have very strong δ++ and δ‐‐ to give strong attraction between the lone pair on the O, N or F and the δ++ H. (LDF is also present but is much weaker.) 4 13. Rank the following for solubility (H, M, L) and explain your answers by analyzing the solvent and solute IMF’s. Explain the reasoning that you used. (5 pts) Solvent: CO2 (l) (O=C=O) LDF, non‐polar Ionic LDF only H‐Bond Extremely “polar” non‐polar polar Lowest solubility Highest Medium Because least like CO2. b/c most similar to CO2. In between the other two extremes. 14. Calculate the pressure required to raise the boiling point of water to 150.0°C, given that the heat of vaporization of water is 41 kJ/mol. (Save the algebra until the end when you are certain you have enough time. (4 pts) P2 = 4.76 atm 15. For each of the following, a) determine the number of valence electrons, and b) draw a Lewis dot structure which obeys the octet rule. (5 pts each) a. PS2+1 (central atom is P) answer: 16 electrons b. BrS2+1 (central atom is Br) answer: 18 electrons 16. Draw one resonance structure for the following structure connected with the correct symbol. (4 pts) 5 17. For the Lewis dot structures below, give the following information for the atom indicated by the arrow: (6 pts) a. name of the shape b) all bond angles c) hybridization of the atom indicated 3
sp , ~109°, bent sp2, trigonal planar, 120° 18. Give an orbital overlap diagram for the following molecule. Label all orbitals used for bonding, label all bonds as σ or π, and clearly indicate on your diagram expected bond angles. (5 pts) See lab diagrams for practice. Bonus: If you were present for the demonstrations, describe what you saw and the scientific principle being demonstrated: a. Slime b. Sodium acetate solution poured on table ...
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This note was uploaded on 11/10/2011 for the course CH 101 taught by Professor Susanbontems during the Fall '11 term at Montgomery College.
- Fall '11