Questions 1-2 Consider the atoms of the following elements. Assume that the atoms are in the ground state. a. S b. Ca c. Ga d. Sb e.

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1 AP Chemistry Fall Semester Practice Exam 5 MULTIPLE CHOICE PORTION: Write the letter for the correct answer to the following questions on the provided answer sheet. Each multiple choice question is worth 2 points. Each set of lettered choices below refers to the numbered statements immediately following it. Select the one lettered choice that best fits each statement. A choice may be used once, more than once, or not at all in each set. Questions 1-2 Consider the atoms of the following elements. Assume that the atoms are in the ground state. a. S b. Ca c. Ga d. Sb e. Br 1. The atom that contains exactly two unpaired electrons 2. The atom that contains only one electron in the highest occupied energy sublevel Questions 3-5 refer to the following molecules. a. CO 2 b. H 2 O c. CH 4 d. C 2 H 4 e. PH 3 3. The molecule with only one double bond 4. The molecule with the largest dipole moment 5. The molecule that has trigonal pyramidal geometry 3 C 2 H 2 (g) C 6 H 6 (g) 6. What is the standard enthalpy change, ΔH, for the reaction represented above? (ΔH f of C 2 H 2 (g) is 230. kj/mol; (ΔH f of C 6 H 6 (g) is 83 kj/mol.) a. 607 kj b. 147 kj c. 19 kj d. +19 kj e kj

2 Pressure (atm) Temperature (degrees Celsius) 7. The phase diagram for the pure substance X is shown above. The temperature of a sample of pure solid X is slowly raised from 10 C to 100 C at a constant pressure of 0.5 atm. What is the expected behavior of the substance? a. It first melts to a liquid and then boils at about 70 C. b. It first melts to a liquid and then boils at about 30 C. c. It melts to a liquid at a temperature of about 25 C and remains a liquid until the temperature is greater than 100 C. d. It sublimes to vapor at an equilibrium temperature of about 25 C. e. It remains a solid until the temperature is greater than 100 C. 8. In which of the following groups are the three species isoelectronic? a. S 2, K +1, Ca +2 b. Sc, Ti, V +2 c. O 2, S 2, Cl 1 d. Mg +2, Ca +2, Sr +2 e. Cs, Ba +2, La Approximately what mass of CuSO 4 5H 2 O (250 g/mol) is required to prepare 250 ml of 0.10 M copper (II) sulfate solution? a. 4.0 g b. 6.2 g c. 34 g d. 85 g e. 140 g 10. Of the following compounds, which is the most ionic? a. SiCl 4

3 b. BrCl c. PCl 3 d. Cl 2 O e. CaCl A solution is made by dissolving a nonvolatile solute in a pure solvent. Compared to the pure solvent, the solution a. has a higher normal boiling point b. has a higher vapor pressure c. has the same vapor pressure d. has a higher freezing point e. is more nearly ideal 12. Which of the following properties generally decreases across the periodic table from sodium to chlorine? a. First ionization energy b. Atomic mass c. Electronegativity d. Maximum value of oxidation number e. Atomic radius 13. What is the mole fraction of ethanol, C 2 H 5 OH, in an aqueous solution that is 46 percent ethanol by mass? (The molar mass of C 2 H 5 OH is 46 g/mol. The molar mass of water is 18 g/mol.) a b c d e According to the VSEPR model, the progressive decrease in the bond angles in the series of molecules CH 4, NH 3, and H 2 O is best accounted for by the a. increasing strength of the bonds b. decreasing size of the central atom c. increasing electronegativity of the central atom d. increasing number of unshared pairs of electrons e. decreasing repulsion between hydrogen atoms 15. The boiling points of the elements helium, neon, argon, krypton, and xenon increase in that order. Which of the following statements accounts for this increase? a. The London (dispersion) forces increase. b. The hydrogen bonding increases. c. The dipole-dipole forces increase. d. The chemical reactivity increases. e. The number of nearest neighbors increases.

4 Questions refer to the graph below. The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase. Temperature t 1 t 2 Time t 3 t 4 t The substance is at its normal freezing point at time a. t 1 b. t 2 c. t 3 d. t 4 e. t Which of the following best describes what happens to the substance between t 4 and t 5? a. The molecules are leaving the liquid phase. b. The solid and liquid phases coexist in equilibrium. c. The vapor pressure f the substance is decreasing. d. The average intermolecular distance is decreasing. e. The temperature of the substance is increasing. 18. 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 +1 ions and OH 1 ions are broken. e. Covalent bonds between H +1 ions and H 2 O molecules become more effective.

5 X(s) X(l) 19. Which of the following is true for any substance undergoing the process represented above at its normal melting point? a. ΔS < 0 b. ΔH = 0 c. ΔH = TΔG d. TΔS = 0 e. ΔH = TΔS Questions refer to the following types of energy. a. Activation energy b. Free energy c. Ionization energy d. Kinetic energy e. Lattice energy 20. The energy required to convert a ground-state atom in the gas phase to a gaseous positive ion. 21. The energy changes that occurs in the conversion of an ionic solid to widely separated gaseous ions. 22. The energy in a chemical or physical change that is available to do useful work. 23. Types of hybridization exhibited by the carbon atoms in propene (CH 3 CHCH 2 ) include which of the following? I. sp II. sp 2 III. sp 3 a. I only b. III only c. I and II only d. II and III only e. I, II, and III 24. The volume of distilled water that should be combined with 10.0 ml of 6.00 M HCl (aq) in order to prepare a M HCl (aq) solution is approximately a ml b ml c ml d ml e ml

6 25. Which of the following pairs of liquids forms the solution that is most ideal (most closely follows Raoult's law)? a. C 8 H 18 and H 2 O b. CH 3 CH 2 CH 2 OH and H 2 O c. CH 3 CH 2 CH 2 OH and C 8 H 18 d. C 6 H 14 and C 8 H 18 e. H 2 SO 4 and H 2 O 26. Ionization Energies for element X (kj/mol) First Second Third Fourth Fifth The ionization energies for element X are listed in the table above. On the basis of the data, element X is most likely to be a. Na b. Mg c. Al d. Si e. P 27. In a molecule in which the central atom exhibits d 2 sp 3 hybrid orbitals, the electron pairs are directed toward the corners of a. a tetrahedron b. a square-based pyramid c. a trigonal bipyramid d. a square e. an octahedron Questions refer to the following diatomic species. a. Li 2 b. B 2 c. N 2 d. O 2 e. F Has the largest bond energy 29. Has a bond order of Contains 1 sigma bond and 2 pi bonds

7 31. Given that a solution is 5 percent sucrose by mass, what additional information is necessary to calculate the molarity of the solution? I. The density of water II. The density of the solution III. The molar mass of sucrose a. I only b. II only c. III only d. I and III e. II and III Question 32 refers to the following reaction and data table. I 2 (g) + 3 Cl 2 (g) 2 ICl 3 (g) Bond Average Bond Energy (kj/mol) I I 150 Cl Cl 240 I Cl According to the data in the table, what is the value of ΔH for the reaction? a. 870 kj b. 390 kj c kj d kj e. + 1,260 kj 33. Which of the following reactions has the largest positive value of ΔS per mole of Cl 2? a. H 2 (g) + Cl 2 (g) 2 HCl (g) b. Cl 2 (g) + ½ O 2 (g) Cl 2 O (g) c. Mg (s) + Cl 2 (g) MgCl 2 (s) d. 2NH 4 Cl (s) N 2 (g) + 4 H 2 (g) + Cl 2 (g) e. Cl 2 (g) 2 Cl (g) 34. The SbCl 5 molecule has trigonal bipyramid structure. Therefore, the hybridization of Sb orbitals should be a. sp 2 b. sp 3 c. dsp 2 d. dsp 3 e. d 2 sp 3

8 35. Which of the following must be true for a reaction that proceeds spontaneously from initial state conditions? a. ΔG > 0 and K > 1 b. ΔG > 0 and K < 1 c. ΔG < 0 and K > 1 d. ΔG < 0 and K < 1 e. ΔG = 0 and K = 1 Question 36 refers to the following reaction. H 2 O (s) H 2 O (l) 36. When ice melts at its normal melting point, which of the following is true for the process? a. ΔH < 0, ΔS > 0, and ΔVolume > 0 b. ΔH < 0, ΔS < 0, and ΔVolume > 0 c. ΔH > 0, ΔS < 0, and ΔVolume < 0 d. ΔH > 0, ΔS > 0, and ΔVolume > 0 e. ΔH > 0, ΔS > 0, and ΔVolume < 0 Questions refer to atoms for which the occupied atomic orbitals are shown below. a. 1s 2s _ b. 1s 2s c. 1s 2s 2p _ d. 1s 2s 2p e. [Ar] 4s 3d _ _ _ _ 37. Represents an atom that is chemically unreactive 38. Represents an atom in an excited state 39. Represents an atom that has four valence electrons 40. Represents an atom of a transition metal

9 ESSAY PORTION: Write your answers on the provided answer sheet. This portion of the exam is worth 20 points. 1. Answer the following questions about the element selenium, Se (atomic number 34). a. Samples of natural selenium contain six stable isotopes. In terms of atomic structure, explain what these isotopes have in common, and how they differ. b. Write the complete electron configuration (e.g., 1s 2 2s 2...etc.) for a selenium atom in the ground state. Indicate the number of unpaired electrons in the ground-state atom, and explain your reasoning. c. In terms of atomic structure, explain why the first ionization energy of selenium is (i) less than that of bromine (atomic number 35), and (ii) greater than that of tellurium (atomic number 52). d. Selenium reacts with fluorine to form SeF 4. Draw the complete Lewis electron-dot structure for SeF 4 and sketch the molecular structure. Indicate whether the molecule is polar or nonpolar, and justify your answer. 2. The reaction represented below is one that contributes significantly to the formation of photochemical smog. 2 NO (g) + O 2 (g) 2 NO 2 (g) ΔH = kj, ΔS = J/K a. Calculate the quantity of heat released when 73.1 g of NO (g) is converted to NO 2 (g). b. For the reaction at 25 C, the value of the standard free-energy change, ΔG, is 70.4 kj. (i) Calculate the value of the equilibrium constant, K, for the reaction at 25 C. (ii) Indicate whether the value of ΔG would become more negative, less negative, or remain unchanged as the temperature is increased. Justify your answer. c. Use the data in the table below to calculate the value of the standard molar entropy, S, for O 2 (g) at 25 C. Standard Molar Entropy, S (J/mol K) NO (g) NO 2 (g) d. Use the date in the table below to calculate the bond energy, in kj/mol, of the nitrogen-oxygen bond in NO 2. Assume that the bonds in the NO 2 molecule are equivalent (i.e., they have the same energy). Bond Energy (kj/mol) Nitrogen-oxygen bond in NO 607 Oxygen-oxygen bond in O Nitrogen-oxygen bond in NO 2?

10 AP Chemistry 2005 Fall Semester Exam Answer Sheet Name Multiple Choice Portion:

11 AP Chemistry 2005 Fall Semester Exam Answer Sheet Essay Portion: Question 1: a. b. c. (i)

12 Question 1 (continued): c. (ii) d. Question 2: a.

13 Question 2 (continued): b. (i) b.(ii) c. d.

51. Pi bonding occurs in each of the following species EXCEPT (A) CO 2 (B) C 2 H 4 (C) CN (D) C 6 H 6 (E) CH 4

Name AP Chemistry: Bonding Multiple Choice 41. Which of the following molecules has the shortest bond length? (A) N 2 (B) O 2 (C) Cl 2 (D) Br 2 (E) I 2 51. Pi bonding occurs in each of the following species