chem 2014
** See graph 17. The potential energy as a function of internuclear distance for three diatomic molecules, X2 , Y2 , and Z2 , is shown in the graph above. Based on the data in the graph, which of the following correctly identifies the diatomic molecules, X2 , Y2 , and Z2 ? X2 Y2 Z2 (A) H2 N2 O2 (B) H2 O2 N2 (C) N2 O2 H2 (D) O2 H2 N2
A
** See graph 27. A student prepared five solutions of CuSO4 with different concentrations, and then filled five cuvettes, each containing one of the solutions. The cuvettes were placed in a spectrophotometer set to the appropriate wavelength for maximum absorbance. The absorbance of each solution was measured and recorded. The student plotted absorbance versus concentration, as shown in the figure above. Which of the following is the most likely explanation for the variance of the data point for the 0.600 M CuSO4 solution? (A) The cuvette into which the 0.600 M solution was placed had some water droplets inside. (B) The cuvette into which the 0.600 M solution was placed was filled slightly more than the other cuvettes. (C) The wavelength setting was accidentally moved away from that of maximum absorbance. (D) The cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer.
D
Refer 40. Which of the following best explains why more energy is required for the process occurring at 110 K than for the process occurring at 90 K ? (A) Intermolecular attractions are completely overcome during vaporization. (B) Intermolecular attractions in the solid phase are weaker than in the liquid phase. (C) Electron clouds of methane molecules are less polarizable at lower temperatures. (D) Vaporization involves a large increase in temperature.
a
** See table 15. Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is (A) greatest in container 1 (B) greatest in container 2 (C) greatest in container 4 (D) the same in containers 1, 2, and 4
A
11. When 200. mL of 2.0 M NaOH(aq) is added to 500. mL of 1.0 M HCl(aq), the pH of the resulting mixture is closest to (A) 1.0 (B) 3.0 (C) 7.0 (D) 13.0
A
18. A 10. g cube of copper at a temperature T1 is placed in an insulated cup containing 10. g of water at a temperature T2 . If T1 > T2 , which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J/(g·°C) and the specific heat of water is 4.18 J/(g·°C).) (A) The temperature of the copper changed more than the temperature of the water. (B) The temperature of the water changed more than the temperature of the copper. (C) The temperature of the water and the copper changed by the same amount. (D) The relative temperature changes of the copper and the water cannot be determined without knowing T1 and T2 .
A
MnO − + 5 Fe2+ + 8 H+ Æ Mn2+ + 5 Fe3+ + 4 H O 26. In the reaction represented above, the number of MnO ions that react must be equal to which of the following? (A) One-fifth the number of Fe2+ ions that are consumed (B) Eight times the number of H+ ions that are consumed (C) Five times the number of Fe3+ ions that are produced (D) One-half the number of H2O molecules that are produced
A
Refer 41. The enthalpy of vaporization of water is 40.7 kJ/mol. Which of the following best explains why the enthalpy of vaporization of methane is less than that of water? (A) Methane does not exhibit hydrogen bonding, but water does. (B) Methane has weaker dispersion forces. (C) Methane has a smaller molar mass. (D) Methane has a much lower density.
A
Refer back 33. Which element is being oxidized during the titration, and what is the element's change in oxidation number? (A) Oxygen, which changes from -1 to 0 (B) Oxygen, which changes from 0 to -2 (C) Manganese, which changes from -1 to +2 (D) Manganese, which changes from +7 to +2
A
See table **** 14. On the basis of the data provided above, the gas in container 3 could be (A) CH4 (B) O2 (C) Ar (D) CO2
A
** Refer back 29. On the basis of the information above, the dissolution of FeF2(s) in acidic solution is (A) thermodynamically favorable, because K2 > 1 (B) thermodynamically favorable, because K3 > 1 (C) not thermodynamically favorable, because K1 < 1 (D) not thermodynamically favorable, because K3 < 1
B
2. Which of the following could be the identity of a white crystalline solid that exhibits the following properties? •It melts at 320∞C. •It does not conduct electricity as a solid. •It conducts electricity in an aqueous solution. (A) C6H12O6(s) (B) NaOH(s) (C) SiO2(s) (D) Cu(s)
B
37. Consider the reaction represented above at 298 K. When equal volumes of N2(g) and H2(g), each at 1 atm, are mixed in a closed container at 298 K, no formation of NH3(g) is observed. Which of the following best explains the observation? (A) The N2(g) and the H2(g) must be mixed in a 1:3 ratio for a reaction to occur. (B) A high activation energy makes the forward reaction extremely slow at 298 K. (C) The reaction has an extremely small equilibrium constant, thus almost no product will form. (D) The reverse reaction has a lower activation energy than the forward reaction, so the forward reaction does not occur.
B
CO(g) + 2 H2(g) ¨↔CH3OH(g) DH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. 22. A 1.0 mol sample of CO(g) and a 1.0 mol sample of H2(g) are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 483 K. Which of the following is true at equilibrium? (A) [H2] = 2[CO] (B) [H2] < [CO] (C) [CO] = [CH3OH] < [H2] (D) [CO] = [CH3OH] = [H2]
B
CO(g) + 2 H2(g) ¨↔CH3OH(g) DH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. 23. A mixture of CO(g) and H2(g) is pumped into a previously evacuated 2.0 L reaction vessel. The total pressure of the reaction system is 1.2 atm at equilibrium. What will be the total pressure of the system if the volume of the reaction vessel is reduced to 1.0 L at constant temperature? (A) Less than 1.2 atm (B) Greater than 1.2 atm but less than 2.4 atm (C) 2.4 atm (D) Greater than 2.4 atm
B
Compound- Molar Mass Na2O- 62.0 MgO- 40.3 K2O- 94.2 CaO-56.1 1.According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen? (A) Na2O (B) MgO (C) K2O (D) CaO
B
M+ is an unknown metal cation with a +1 charge. A student dissolves the chloride of the unknown metal, MCl, in enough water to make 100.0 mL of solution. The student then mixes the solution with excess AgNO3 solution, causing AgCl to precipitate. The student collects the precipitate by filtration, dries it, and records the data shown below. (The molar mass of AgCl is 143 g/mol.) Mass of unknown chloride, MCl 0.74 g Mass of filter paper 0.80 g Mass of filter paper plus AgCl precipitate 2.23 g 8. What is the identity of the metal chloride? (A) NaCl (B) KCl (C) CuCl (D) LiCl
B
NO(g) + NO3(g) 2 NO2(g) rate = k [NO][NO3] 50. The reaction represented above occurs in a single step that involves the collision between a particle of NO and a particle of NO3 . A scientist correctly calculates the rate of collisions between NO and NO3 that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy? (A) The energy of collisions between two reactant particles is frequently absorbed by collision with a third particle. (B) The two reactant particles must collide with a particular orientation in order to react. (C) The activation energy for a reaction is dependent on the concentrations of the reactant particles. (D) The activation energy for a reaction is dependent on the temperature.
B
Refer 43. Consider the reaction represented by the equation 2 X + 2 Z Æ X2Z2 . During a reaction in which a large excess of reactant X was present, the concentration of reactant Z was monitored over time. A plot of the natural logarithm of the concentration of Z versus time is shown in the figure above. The order of the reaction with respect to reactant Z is (A) zero order (B) first order (C) second order (D) third order
B
Refer 38. Data collected during the titration of a 20.0 mL sample of a 0.10 M solution of a monoprotic acid with a solution of NaOH of unknown concentration are plotted in the graph above. Based on the data, which of the following are the approximate pKa of the acid and the molar concentration of the NaOH? pKa [NaOH] (A) 4.7 0.050 M (B) 4.7 0.10 M (C) 9.3 0.050 M (D) 9.3 0.10 M
B
Refer 39. How much energy is required to melt 64 g of methane at 90 K? (The molar mass of methane is 16 g/mol.) (A) 0.24 kJ (B) 3.8 kJ (C) 33 kJ (D) 60. kJ
B
Refer back 31. A sample containing atoms of C and F was analyzed using x-ray photoelectron spectroscopy. The portion of the spectrum showing the 1s peaks for atoms of the two elements is shown above. Which of the following correctly identifies the 1s peak for the F atoms and provides an appropriate explanation? (A) Peak X, because F has a smaller first ionization energy than C has. (B) Peak X, because F has a greater nuclear charge than C has. (C) Peak Y, because F is more electronegative than C is. (D) Peak Y, because F has a smaller atomic radius than C has.
B
refer 45. Which of the following best describes the flow of heat when 1.0 mol of XY2 decomposes? (A) 50 kJ of heat is transferred to the surroundings. (B) 50 kJ of heat is transferred from the surroundings. (C) 100 kJ of heat is transferred to the surroundings. (D) 100 kJ of heat is transferred from the surroundings.
B
refer 49. The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points? (A) Butane < 1-propanol < acetone (B) Butane < acetone < 1-propanol (C) 1-propanol < acetone < butane (D) Acetone = butane < 1-propanol
B
* See diagram 7. The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure P1 , as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2 . What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample? (A) The average kinetic energy increases. (B) The average kinetic energy decreases. (C) The average kinetic energy stays the same. (D) It cannot be determined how the kinetic energy is affected without knowing P1 and P2 .
C
** Refer back 28. Based on the information above, which of the following is true? (A) Only mechanism 1 is consistent with the rate law. (B) Only mechanism 2 is consistent with the rate law. (C) Both mechanism 1 and mechanism 2 are consistent with the rate law. (D) Neither mechanism 1 nor mechanism 2 is consistent with the rate law.
C
** See table 12. The table above shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionization energy of oxygen from the overall trend? (A) The atomic radius of oxygen is greater than the atomic radius of fluorine. (B) The atomic radius of oxygen is less than the atomic radius of nitrogen. (C) There is repulsion between paired electrons in oxygen's 2p orbitals. (D) There is attraction between paired electrons in oxygen's 2p orbitals.
C
** See table 16. The best explanation for the lower pressure in container 4 is that SO2 molecules (A) have a larger average speed than the other three gases (B) occupy a larger portion of the container volume than the other three gases (C) have stronger intermolecular attractions than the other three gases (D) contain bonds, while the other gases contain only bonds
C
13. Which of the following equations represents a reaction for which the standard entropy change is positive (DS > 0) ? (A) 3 O2(g) -->2 O3(g) (B) 2 H2(g) + O2(g) -->2 H2O(l) (C) CaCO3(s) -->CaO(s) + CO2(g) (D) I2(g) + 2 K(s) ---> 2 KI(s)
C
19. A solution containing HCl and the weak acid HClO2 has a pH of 2.4. Enough KOH(aq) is added to the solution to increase the pH to 10.5. The amount of which of the following species increases as the KOH(aq) is added? (A) Cl-(aq) (B) H+(aq) (C) ClO -(aq) (D) HClO2(aq)
C
25. A solution is prepared by adding 100 mL of 1.0 M HC2H3O2(aq) to 100 mL of 1.0 M NaC2H3O2(aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0 M HCl are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH? (A) H3O+(aq) + OH(aq) ↔2 H2O(l) (B) H3O+(aq) + Cl(aq) ↔HCl(g) + H2O(l) (C) H3O+(aq) + C2H3O2(aq) ↔HC2H3O2(aq) + H2O(l) (D) H3O+(aq) + HC2H3O2(aq) ↔H2C2H3O2+(aq) + H2O(l)
C
5. Which of the following best helps to explain why the value of H for the dissolving of CaF2 in water is positive? (A) CaF2(s) is insoluble in water. (B) CaF2(s) dissolves in water to form CaF2(aq) particles. (C) Ca2+ ions have very strong ion-ion interactions with F ions in the crystal lattice. (D) Ca2+ ions have very strong ion-dipole interactions with water molecules in the solution.
C
6. Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas? (A) 50 K and 0.10 atm (B) 50 K and 5.0 atm (C) 500 K and 0.10 atm (D) 500 K and 50 atm
C
C3H8(g) + 4 Cl2(g) Æ C3H4Cl4(g) + 4 HCl(g) 48. A 6.0 mol sample of C3H8(g) and a 20. mol sample of Cl2(g) are placed in a previously evacuated vessel, where they react according to the equation above. After one of the reactants has been totally consumed, how many moles of HCl(g) have been produced? (A) 4.0 mol (B) 8.0 mol (C) 20. mol (D) 24 mol
C
CO(g) + 2 H2(g) ¨↔CH3OH(g) DH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. 21. Which of the following explains the effect on the equilibrium constant, Kc , when the temperature of the reaction system is increased to 650 K? (A) Kc will increase because the activation energy of the forward reaction increases more than that of the reverse reaction. (B) Kc will increase because there are more reactant molecules than product molecules. (C) Kc will decrease because the reaction is exothermic. (D) Kc is constant and will not change.
C
CO(g) + 2 H2(g) ¨↔CH3OH(g) DH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. 24. Which of the following statements is true about bond energies in this reaction? (A) The energy absorbed as the bonds in the reactants are broken is greater than the energy released as the bonds in the product are formed. (B) The energy released as the bonds in the reactants are broken is greater than the energy absorbed as the bonds in the product are formed. (C) The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed. (D) The energy released as the bonds in the reactants are broken is less than the energy absorbed as the bonds in the product are formed.
C
PCl3(g) + Cl2(g) ¨Æ PCl5(g) Kc = 6.5 36. At a certain point in time, a 1.00 L rigid reaction vessel contains 1.5 mol of PCl3(g), 1.0 mol of Cl2(g), and 2.5 mol of PCl5(g). Which of the following describes how the measured pressure in the reaction vessel will change and why it will change that way as the reaction system approaches equilibrium at constant temperature? (A) The pressure will increase because Q < Kc . (B) The pressure will increase because Q > Kc . (C) The pressure will decrease because Q < Kc . (D) The pressure will decrease because Q > Kc .
C
refer 46. The reaction is thermodynamically favorable under standard conditions at 298 K. Therefore, the value of S for the reaction must be (A) equal to zero (B) equal to DH/ 298 K (C) greater than DH/ 298 K (D) less than DH/ 298 K
C
refer back 34. Which of the following best describes what happens to the pH of the H2O2 solution as the titration proceeds? (A) The +2 charge on the manganese ions maintains the acidity of the solution. (B) The production of water dilutes the solution, making it basic. (C) As H+ ions are consumed, the solution becomes less acidic and the pH increases. (D) As H+ ions are consumed, the solution becomes less acidic and the pH decreases.
C
2 BaO2(s) ¨Æ 2 BaO(s) + O2(g) DH∞ = 162 kJ/molrxn 4. A sealed rigid vessel contains BaO2(s) in equilibrium with BaO(s) and O2(g) as represented by the equation above. Which of the following changes will increase the amount of BaO2(s) in the vessel? (A) Removing a small amount of O2(g) (B) Removing a small amount of BaO(s) (C) Adding He gas to the vessel (D) Lowering the temperature
D
2 H2O(l) ¨Æ H3O+(aq) + OH-(aq) 20. The autoionization of water is represented by the equation above. Values of pKw at various temperatures are listed in the table below. Temp - pka 0- 14.9 10- 14.5 20- 14.2 30- 13.8 40- 13.5 Based on the information above, which of the following statements is true? (A) The dissociation of water is an exothermic process. (B) The pH of pure water is 7.00 at any temperature. (C) As the temperature increases, the pH of pure water increases. (D) As the temperature increases, the pH of pure water decreases.
D
3. Which of the following correctly identifies which has the higher first-ionization energy, Cl or Ar, and supplies the best justification? (A) Cl, because of its higher electronegativity (B) Cl, because of its higher electron affinity (C) Ar, because of its completely filled valence shell (D) Ar, because of its higher effective nuclear charge
D
35. The BF3 molecule is nonpolar, whereas the NF3 statements accounts for the difference in polarity of the two molecules? molecule is polar. Which of the following (A) In NF3, each F is joined to N with multiple bonds, whereas in BF3 , each F is joined to B with single bonds. (B) N F bonds are polar, whereas B F bonds are nonpolar. (C) NF3 is an ionic compound, whereas BF3 is a molecular compound. (D) Unlike BF3, NF3 has a nonplanar geometry due to an unshared pair of electrons on the N atom.
D
M+ is an unknown metal cation with a +1 charge. A student dissolves the chloride of the unknown metal, MCl, in enough water to make 100.0 mL of solution. The student then mixes the solution with excess AgNO3 solution, causing AgCl to precipitate. The student collects the precipitate by filtration, dries it, and records the data shown below. (The molar mass of AgCl is 143 g/mol.) Mass of unknown chloride, MCl 0.74 g Mass of filter paper 0.80 g Mass of filter paper plus AgCl precipitate 2.23 g 9. During the course of the experiment, which of the following happens to the NO - ions? (A) They are oxidized by Cl- ions. (B) They are reduced to NO - ions. (C) They are decomposed by reacting with M+ ions. (D) They remain dissolved in the filtrate solution.
D
Refer back 30. Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds. Which of the following diagrams shows the correct representation of the hydrogen bonding (denoted by dashed lines) between thymine and adenine base pairs? (In each diagram, thymine is shown at the left and adenine is shown at the right. The bases are attached to the backbone portion of the DNA strands.)
D
Refer back 32. At a certain time during the titration, the rate of appearance of O2(g) was 1.0 ¥ 10-3 mol/(L· s). What was the rate of disappearance of MnO - at the same time? (A) 6.0 ¥ 10-3 mol/(L· s) (B) 4.0 ¥ 10-3 mol/(L· s) (C) 6.0 ¥ 10-4 mol/(L· s) (D) 4.0 ¥ 10-4 mol/(L· s)
D
refer 44. Which of the following most likely accounts for the difference between reaction path one and reaction path two? (A) A higher temperature in path one (B) A higher temperature in path two (C) The presence of a catalyst in path one (D) The presence of a catalyst in path two
D