Chem Final

A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a pH meter and graphed as a function of the volume of 0.100 M NaOH added. 14. At point R in the titration, which of the following species has the highest concentration? (A) HA (B) A- (C)H3O+ (D) OH-

A. HA

The experimental apparatus represented above is used to demonstrate the rates at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse from each end and meet somewhere in between, where they react to form a white solid. Which of the following combinations will produce a solid closest to the center of the tube? (A) HCl and CH3NH2 (B) HCl and NH3 (C) HBr and CH3NH2 (D) HBr and NH3

A. HCl and CH3NH2

4. Zn(s) is used to reduce other compounds in chemical reactions. If a chemist needs a substance that is more effective in its reducing ability, which of the following species would be the best choice? (A) Na (B) H+ (C) K+ (D) Cl-

A. Na

NaF MgO Boiling Point (∞C) 1695 3600 Na+ Mg2+ F− Cl− O2− Ionic Radius (pm) 76 72 133 181 140 Based on the data in the tables above, which of the following statements provides the best prediction for the boiling point of NaCl ? (A) NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF . (B) NaCl will have a boiling point between that of NaF and MgO because the covalent character of the bonds in NaCl is intermediate between that of MgO and NaF. (C) NaCl will have a higher boiling point than MgO because the ions are spaced farther apart in NaCl. (D) NaCl will have a higher boiling point than MgO because the energy required to transfer electrons from the anion to the cation is larger in NaCl than in MgO .

A. NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF .

Silicon crystals are semiconductors. Which of the following is a correct reason for the increase in the conductivity of Si crystals when a small fraction of Si atoms are replaced with those of a different element? (A) P atoms introduce additional mobile negative charges. (B) P atoms introduce additional mobile positive charges. (C) Ge atoms have more electrons than Si atoms have. (D) Ge atoms are much smaller than Si atoms.

A. P atoms introduce additional mobile negative charges.

Step 1: Cl(g) + O3(g) Æ ClO(g) + O2(g) Step 2: ClO(g) + O(g) Æ Cl(g) + O2(g) A proposed mechanism for destruction of ozone gas in the stratosphere is represented above. Which of the following is evidence that the mechanism is occurring? (A) The presence of Cl(g) increases the rate of the overall reaction. (B) The presence of Cl(g) decreases the rate of the overall reaction. (C) The presence of Cl(g) increases the equilibrium constant of the overall reaction. (D) The presence of Cl(g) decreases the equilibrium constant of the overall reaction.

A. The presence of Cl(g) increases the rate of the overall reaction.

K(s) + 1 2 Cl2(g) Æ KCl(s) ∆H° = − 437 kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Process DH° (kJ/molrxn) K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z It is observed that the reaction producing KCl from its elements goes essentially to completion. Which of the following is a true statement about the thermodynamic favorability of the reaction? (A) The reaction is favorable and driven by an enthalpy change only. (B) The reaction is unfavorable and driven by an entropy change only. (C) The reaction is favorable and driven by both enthalpy and entropy changes. (D) The reaction is unfavorable due to both enthalpy and entropy changes.

A. The reaction is favorable and driven by an enthalpy change only.

Ion Ionic Radius (pm) Zn2+ 74 Ca2+ 100 Ba2+ 135 Based on the data in the table above, which of the following correctly predicts the relative strength of the attraction of Zn2+, Ca2+, and Ba2+ ions to water molecules in a solution, from strongest to weakest, and provides the correct reason? (A) Zn2+ > Ca2+ > Ba2+ because the smaller ions have a stronger coulombic attraction to water (B) Zn2+ > Ca2+ > Ba2+ because the smaller ions are more electronegative (C) Ba2+ > Ca2+ > Zn2+ because the larger ions are more polarizable (D) Ba2+ > Ca2+ > Zn2+ because the larger ions are less electronegative

A. Zn2+ > Ca2+ > Ba2+ because the smaller ions have a stronger coulombic attraction to water

Concentration (M) pH of Acid 1 pH of Acid 2 pH of Acid 3 pH of Acid 4 0.010 3.44 2.00 2.92 2.20 0.050 3.09 1.30 2.58 1.73 0.10 2.94 1.00 2.42 1.55 0.50 2.69 0.30 2.08 1.16 1.00 2.44 0.00 1.92 0.98 The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. For which acid is the value of the aciddissociation constant, Ka , the smallest? (A) Acid 1 (B) Acid 2 (C) Acid 3 (D) Acid 4

A. acid 1

The mass percent of carbon in pure glucose, C6H12O6, is 40.0 percent. A chemist analyzes an impure sample of glucose and determines that the mass percent of carbon is 38.2 percent. Which of the following impurities could account for the low mass percent of carbon in the sample? (A) Water, H2O (B) Ribose, C5H10O5 (C) Fructose, C6H12O6, an isomer of glucose (D) Sucrose, C12H22O11

A. water, H2O

PCl5(g) ¨Æ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Additional Cl2(g) is injected into the system at equilibrium. Which of the following graphs best shows the rate of the reverse reaction as a function of time? (Assume that the time for injection and mixing of the additional Cl2(g) is negligible.)

B

Which of the following is the best particulate representation of the species (other than H2O) that are present in significant concentrations in the solution at point U in the titration?

B

COCl2(g) ¨Æ CO(g) + Cl2(g) COCl2(g) decomposes according to the equation above. When pure COCl2(g) is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of Kp for the reaction at 690 K? (A) 0.040 (B) 0.050 (C) 0.80 (D) 1.0

B. 0.050

Half-cell 1: strip of Al(s) in 1.00 M Al(NO3)3(aq) Half-cell 2: strip of Cu(s) in 1.00 M Cu(NO3)2(aq) Half-cell 3: strip of Fe(s) in 1.00 M Fe(NO3)2(aq) Galvanic Cell Half-cells Cell Reaction Ecell D (V) X 1 and 2 2 Al(s) + 3 Cu2+(aq) Æ 2 Al3+(aq) + 3 Cu(s) 2.00 Y 1 and 3 2 Al(s) + 3 Fe2+(aq) Æ 2 Al3+(aq) + 3 Fe(s) 1.22 Z 2 and 3 Fe(s) + Cu2+(aq) Æ Fe2+(aq) + Cu(s) ? What is the standard cell potential of galvanic cell Z? (A) 0.26 V (B) 0.78 V (C) 2.34 V (D) 3.22 V

B. 0.78 V

Which of the following reactions is not thermodynamically favored at low temperatures but becomes favored as the temperature increases? Reaction DH° (kJ/molrxn) DS° (J/(molrxnK)) (A) 2 CO(g) + O2(g) Æ 2 CO2(g) −566 −173 (B) 2 H2O(g) Æ 2 H2(g) + O2(g) 484 90.0 (C) 2 N2O(g) Æ 2 N2(g) + O2(g) −164 149 (D) PbCl2(s) Æ Pb2+(aq) + 2 Cl¯(aq) 23.4 −12.5

B. 2 H2O(g) Æ 2 H2(g) + O2(g) 484 90.0

PCl5(g) ¨Æ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. If the decomposition reaction were to go to completion, the total pressure in the container would be (A) 1.4 atm (B) 2.0 atm (C) 2.8 atm (D) 3.0 atm

B. 2.0 atm

Element Atomic Radius First Ionization Energy Calcium 194 pm 590 kJ/mol Potassium — — Based on periodic trends and the data in the table above, which of the following are the most probable values of the atomic radius and the first ionization energy for potassium, respectively? (A) 242 pm, 633 kJ/mol (B) 242 pm, 419 kJ/mol (C) 120 pm, 633 kJ/mol (D) 120 pm, 419 kJ/mol

B. 242 pm, 419 kJ/mol

The figure above represents three sealed 1.0 L vessels, each containing a different inert gas at 298 K. The pressure of Ar in the first vessel is 2.0 atm. The ratio of the numbers of Ar, Ne, and He atoms in the vessels is 2:1:6, respectively. After all the gases are combined in a previously evacuated 2.0 L vessel, what is the total pressure of the gases at 298 K? (A) 3.0 atm (B) 4.5 atm (C) 9.0 atm (D) 18 atm

B. 4.5 atm

The figure above shows that in solid hydrogen fluoride there are two different distances between H atoms and F atoms. Which of the following best accounts for the two different distances? (A) Accommodation of the necessary bond angles in the formation of the solid (B) Difference in strength between covalent bonds and intermolecular attractions (C) Different isotopes of fluorine present in the samples (D) Uneven repulsions among nonbonding electron pairs

B. Difference in strength between covalent bonds and intermolecular attractions

H2C2O4(aq) + H2O(l) ¨Æ H3O+(aq) + HC2O4 −(aq) HC2O4 −(aq) + H2O(l) ¨Æ H3 O+(aq) + C2O4 2−(aq) H2O(l) + H2O(l) ¨Æ H3O+(aq) + OH−(aq) 11. All the reactions represented above occur in an aqueous solution of oxalic acid. Which of the following represent a Brønsted-Lowry conjugate acid-base pair? (A) H2C2O4(aq) and C2O42-(aq) (B) HC2O4−(aq) and C2O42-(aq) (C) HC2O4-(aq) and H2O(aq) (D) H3O+(aq) and OH−(aq)

B. HC2O4−(aq) and C2O42-(aq)

PCl5(g) ¨Æ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Which of the following statements about Kp , the equilibrium constant for the reaction, is correct? (A) Kp > 1 (B) Kp < 1 (C) Kp = 1 (D) It cannot be determined whether Kp > 1, Kp < 1, or Kp = 1 without additional information.

B. Kp < 1

H2(g) + I2(g) ¨Æ 2 HI(g) At 450∞C, 2.0 moles each of H2(g), I2(g), and HI(g) are combined in a 1.0 L rigid container. The value of Kc at 450∞C is 50. Which of the following will occur as the system moves toward equilibrium? (A) More H2(g) and I2(g) will form. (B) More HI(g) will form. (C) The total pressure will decrease. (D) No net reaction will occur, because the number of molecules is the same on both sides of the equation.

B. More HI(g) will form.

A student carries out the same titration, but uses an indicator instead of a pH meter. If the indicator changes color slightly past the equivalence point, what will the student obtain for the calculated concentration of the acid? (A) Slightly less than 0.0800 M (B) Slightly more than 0.0800 M (C) Slightly less than 0.125 M (D) Slightly more than 0.125 M

B. Slightly more than 0.0800 M

2 N2O5(g) Æ 4 NO2(g) + O2(g) A sample of N2O5 was placed in an evacuated container, and the reaction represented above occurred. The value of N O2 5 P , the partial pressure of N2O5(g), was measured during the reaction and recorded in the table below. Time (min) N O2 5 P (atm) ln( N O2 5 P ) N O2 5 1 P (atm−1 ) 0 150 5.0 0.0067 100 75 4.3 0.013 200 38 3.6 0.027 300 19 2.9 0.053 Which of the following correctly describes the reaction? (A) The decomposition of N2O5 is a zero-order reaction. (B) The decomposition of N2O5 is a first-order reaction. (C) The decomposition of N2O5 is a second-order reaction. (D) The overall reaction order is 3.

B. The decomposition of N2O5 is a first-order reaction.

A 100 g sample of a metal was heated to 100∞C and then quickly transferred to an insulated container holding 100 g of water at 22∞C. The temperature of the water rose to reach a final temperature of 35∞C. Which of the following can be concluded? (A) The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained. (B) The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained. (C) The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water. (D) The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

B. The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

Concentration (M) pH of Acid 1 pH of Acid 2 pH of Acid 3 pH of Acid 4 0.010 3.44 2.00 2.92 2.20 0.050 3.09 1.30 2.58 1.73 0.10 2.94 1.00 2.42 1.55 0.50 2.69 0.30 2.08 1.16 1.00 2.44 0.00 1.92 0.98 The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. Which of the four acids listed in the table is hydrochloric acid? (A) Acid 1 (B) Acid 2 (C) Acid 3 (D) Acid 4

B. acid 2

Container A B C Gas Methane Ethane Butane Formula CH4 C2H6 C4H10 Molar mass (g/mol) 16 30. 58 Temperature (∞C) 27 27 27 Pressure (atm) 2.0 4.0 2.0 The density of the gas, in g/L, is (A) greatest in container A (B) greatest in container B (C) greatest in container C (D) the same in all three containers

B. greatest in container B

K(s) + 1 2 Cl2(g) Æ KCl(s) ∆H° = − 437 kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Process DH° (kJ/molrxn) K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z Which of the values of DH∞ for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process) ? (A) z only (B) y and z only (C) x, y, and z only (D) w, x, y, and z

B. y and z only

Ag+(aq) + Cl−(aq) ¨Æ AgCl(s) A student mixes dilute AgNO3(aq) with excess NaCl(aq) to form AgCl(s), as represented by the net ionic equation above. Which of the diagrams below best represents the ions that are present in significant concentrations in the solution? (Ksp for AgCl is 1.8 ¥ 10−10.)

C

Concentration (M) pH of Acid 1 pH of Acid 2 pH of Acid 3 pH of Acid 4 0.010 3.44 2.00 2.92 2.20 0.050 3.09 1.30 2.58 1.73 0.10 2.94 1.00 2.42 1.55 0.50 2.69 0.30 2.08 1.16 1.00 2.44 0.00 1.92 0.98 The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. A 25 mL sample of a 1.0 M solution of acid 1 is mixed with 25 mL of 0.50 M NaOH. Which of the following best explains what happens to the pH of the mixture when a few drops of 1.0 M HNO3 are added? (A) The pH of the mixture increases sharply, because HNO3 is a strong acid. (B) The pH of the mixture decreases sharply, because H3O+ ions were added. (C) The pH of the mixture stays about the same, because the conjugate base of acid 1 reacts with the added H3O+ ions. (D) The pH of the mixture stays about the same, because the OH− ions in the solution react with the added H3O+ ions.

C

Which of the following particulate diagrams best shows the formation of water vapor from hydrogen gas and oxygen gas in a rigid container at 125∞C ?

C

K(s) + 1 2 Cl2(g) Æ KCl(s) ∆H° = − 437 kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Process DH° (kJ/molrxn) K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z How much heat is released or absorbed when 0.050 mol of Cl2(g) is formed from KCl(s)? (A) 87.4 kJ is released (B) 43.7 kJ is released (C) 43.7 kJ is absorbed (D) 87.4 kJ is absorbed

C. 43.7 kJ is absorbed

PCl5(g) ¨Æ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Which of the following is the most likely cause for the increase in pressure observed in the container as the reaction reaches equilibrium? (A) A decrease in the strength of intermolecular attractions among molecules in the flask (B) An increase in the strength of intermolecular attractions among molecules in the flask (C) An increase in the number of molecules, which increases the frequency of collisions with the walls of the container (D) An increase in the speed of the molecules that then collide with the walls of the container with greater force

C. An increase in the number of molecules, which increases the frequency of collisions with the walls of the container

Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the molecular formula of the compound? (A) C2H2 (B) C2H6 (C) C4H8 (D) C6H6

C. C4H8

Substance Equilibrium Vapor Pressure at 20°C (torr) C6H6(l) 75 C2H5OH(l) 44 CH3OH(l) 92 C2H6O2(l) 0.06 2. Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces? (A) C6H6(l) (B) C2H5OH(l) (C) CH3OH(l) (D) C2H6O2(l)

C. CH3OH(l)

Element Metallic Radius (pm) Melting Point (∞C) Common Oxidation State Au 144 1064 1+, 3+ Cu 128 1085 1+, 2+ Ag 144 961 1+ 42. To make Au stronger and harder, it is often alloyed with other metals, such as Cu and Ag. Consider two alloys, one of Au and Cu and one of Au and Ag, each with the same mole fraction of Au. If the Au/Cu alloy is harder than the Au/Ag alloy, then which of the following is the best explanation based on the information in the table above? (A) Cu has two common oxidation states, but Ag has only one. (B) Cu has a higher melting point than Au has, but Ag has a lower melting point than Au has. (C) Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy. (D) Cu atoms are less polarizable than are Au or Ag atoms, thus Cu has weaker interparticle forces.

C. Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy.

Acid Structure Ka HNO2 4.0 ¥10−4 HC3H5O2 1.3 ¥10−5 HClO 3.0 ¥10−8 HOC6H5 1.6 ¥10−10 The table above shows the values of Ka for four weak acids. Which of the following pairs of chemical species, when combined in equimolar amounts, results in a buffer with a pH closest to 7.5 ? (A) HNO2 and OH− (B) HC3H5O2 and C3H5O2 − (C) HClO and ClO− (D) C6H5OH and C6H5O−

C. HClO and ClO−

The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. All of the following statements are true. Which one would be the best basis for concluding that the sample was pure Te? (A) Te forms ions with a −2 charge, whereas I forms ions with a −1 charge. (B) Te is more abundant than I in the universe. (C) I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope. (D) I has a higher first ionization energy than Te does.

C. I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope.

The diagram above shows molecules of Br2 and I2 drawn to the same scale. Which of the following is the best explanation for the difference in the boiling points of liquid Br2 and I2 , which are 59∞C and 184∞C, respectively? (A) Solid iodine is a network covalent solid, whereas solid bromine is a molecular solid. (B) The covalent bonds in I2 molecules are weaker than those in Br2 molecules. (C) I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2 . (D) Bromine has a greater electronegativity than iodine, thus there are stronger dipole-dipole forces in liquid bromine than in liquid iodine.

C. I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2 .

K(s) + 1 2 Cl2(g) Æ KCl(s) ∆H° = − 437 kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Process DH° (kJ/molrxn) K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z What remains in the reaction vessel after equal masses of K(s) and Cl2(g) have reacted until either one or both of the reactants have been completely consumed? (A) KCl only (B) KCl and K only (C) KCl and Cl2 only (D) KCl, K, and Cl2

C. KCl and Cl2 only

Half-cell 1: strip of Al(s) in 1.00 M Al(NO3)3(aq) Half-cell 2: strip of Cu(s) in 1.00 M Cu(NO3)2(aq) Half-cell 3: strip of Fe(s) in 1.00 M Fe(NO3)2(aq) Galvanic Cell Half-cells Cell Reaction Ecell D (V) X 1 and 2 2 Al(s) + 3 Cu2+(aq) Æ 2 Al3+(aq) + 3 Cu(s) 2.00 Y 1 and 3 2 Al(s) + 3 Fe2+(aq) Æ 2 Al3+(aq) + 3 Fe(s) 1.22 Z 2 and 3 Fe(s) + Cu2+(aq) Æ Fe2+(aq) + Cu(s) ? In galvanic cells Y and Z, which of the following takes place in half-cell 3 ? (A) Reduction occurs in both cell Y and cell Z. (B) Oxidation occurs in both cell Y and cell Z. (C) Reduction occurs in cell Y, and oxidation occurs in cell Z. (D) Oxidation occurs in cell Y, and reduction occurs in cell Z.

C. Reduction occurs in cell Y, and oxidation occurs in cell Z.

At which point on the titration curve is [A-] closest to twice that of [HA] ? (A) R (B) S (C) T (D) U

C. T

Consider the molecules represented above and the data in the table below. Nonane and 2,3,4-trifluoropentane have almost identical molar masses, but nonane has a significantly higher boiling point. Which of the following statements best helps explain this observation? (A) The C-F bond is easier to break than the C-H bond. (B) The C-F bond is more polar than the C-H bond. (C) The carbon chains are longer in nonane than they are in 2,3,4-trifluoropentane. (D) The carbon chains are farther apart in a sample of nonane than they are in 2,3,4-trifluoropentane. Compound Molecular Formula Molar Mass (g/mol) Boiling Point (°C) Nonane C9H20 128 151 2,3,4-trifluoropentane C5H9F3 126 89

C. The carbon chains are longer in nonane than they are in 2,3,4-trifluoropentane.

Half-cell 1: strip of Al(s) in 1.00 M Al(NO3)3(aq) Half-cell 2: strip of Cu(s) in 1.00 M Cu(NO3)2(aq) Half-cell 3: strip of Fe(s) in 1.00 M Fe(NO3)2(aq) Galvanic Cell Half-cells Cell Reaction Ecell D (V) X 1 and 2 2 Al(s) + 3 Cu2+(aq) Æ 2 Al3+(aq) + 3 Cu(s) 2.00 Y 1 and 3 2 Al(s) + 3 Fe2+(aq) Æ 2 Al3+(aq) + 3 Fe(s) 1.22 Z 2 and 3 Fe(s) + Cu2+(aq) Æ Fe2+(aq) + Cu(s) ? If the half-cell containing 1.00 M Fe(NO3)2(aq) in galvanic cells Y and Z is replaced with a half-cell containing 5.00 M Fe(NO3)2(aq), what will be the effect on the cell voltage of the two galvanic cells? (A) The voltage will increase in both cells. (B) The voltage will decrease in both cells. (C) The voltage will increase in cell Y and decrease in cell Z. (D) The voltage will decrease in cell Y and increase in cell Z.

C. The voltage will increase in cell Y and decrease in cell Z.

N2 molecules absorb ultraviolet light but not visible light. I2 molecules absorb both visible and ultraviolet light. Which of the following statements explains the observations? (A) More energy is required to make N2 molecules vibrate than is required to make I2 molecules vibrate. (B) More energy is required to remove an electron from an I2 molecule than is required to remove an electron from a N2 molecule. (C) Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule. (D) The molecular mass of I2 is greater than the molecular mass of N2 .

C. Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule.

Concentration (M) pH of Acid 1 pH of Acid 2 pH of Acid 3 pH of Acid 4 0.010 3.44 2.00 2.92 2.20 0.050 3.09 1.30 2.58 1.73 0.10 2.94 1.00 2.42 1.55 0.50 2.69 0.30 2.08 1.16 1.00 2.44 0.00 1.92 0.98 The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. Of the following species, which has the greatest concentration in a 1.0 M solution of acid 1 at equilibrium? (A) OH− (B) H3O+ (C) Acid 1 (D) The conjugate base of acid 1

C. acid 1

Container A B C Gas Methane Ethane Butane Formula CH4 C2H6 C4H10 Molar mass (g/mol) 16 30. 58 Temperature (∞C) 27 27 27 Pressure (atm) 2.0 4.0 2.0 If the pressure of each gas is increased at constant temperature until condensation occurs, which gas will condense at the lowest pressure? (A) Methane (B) Ethane (C) Butane (D) All the gases will condense at the same pressure.

C. butane

PCl5(g) ¨Æ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. As the reaction progresses toward equilibrium, the rate of the forward reaction (A) increases until it becomes the same as the reverse reaction rate at equilibrium (B) stays constant before and after equilibrium is reached (C) decreases to become a constant nonzero rate at equilibrium (D) decreases to become zero at equilibrium

C. decreases to become a constant nonzero rate at equilibrium

K(s) + 1 2 Cl2(g) Æ KCl(s) ∆H° = − 437 kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Process DH° (kJ/molrxn) K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z Cl2(g) + 2 e− Æ 2 Cl−(g) Which of the following expressions is equivalent to DH∞ for the reaction represented above? (A) x + y (B) x - y (C) x + 2y (D) 2 x - y

C. x + 2y

The graph above shows the speed distribution of molecules in a sample of a gas at a certain temperature. Which of the following graphs shows the speed distribution of the same molecules at a lower temperature (as a dashed curve) ?

D

Caffeine (C8H10N4O2) is a weak base with a Kb value of 4 ¥ 10-4 . The pH of a 0.01 M solution of caffeine is in the range of (A) 2-3 (B) 5-6 (C) 7-8 (D) 11-12

D. 11-12

Beaker X and beaker Y each contain 1.0 L of solution, as shown above. A student combines the solutions by pouring them into a larger, previously empty beaker Z and observes the formation of a white precipitate. Assuming that volumes are additive, which of the following sets of solutions could be represented by the diagram above? Beaker X Beaker Y Beaker Z (A) 2.0 M AgNO3 2.0 M MgCl2 4.0 M Mg(NO3)2 and AgCl(s) (B) 2.0 M AgNO3 2.0 M MgCl2 2.0 M Mg(NO3)2 and AgCl(s) (C) 2.0 M AgNO3 1.0 M MgCl2 1.0 M Mg(NO3)2 and AgCl(s) (D) 2.0 M AgNO3 1.0 M MgCl2 0.50 M Mg(NO3)2 and AgCl(s)

D. 2.0 M AgNO3 1.0 M MgCl2 0.50 M Mg(NO3)2 and AgCl(s)

Concentration (M) pH of Acid 1 pH of Acid 2 pH of Acid 3 pH of Acid 4 0.010 3.44 2.00 2.92 2.20 0.050 3.09 1.30 2.58 1.73 0.10 2.94 1.00 2.42 1.55 0.50 2.69 0.30 2.08 1.16 1.00 2.44 0.00 1.92 0.98 The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. If equal volumes of the four acids at a concentration of 0.50 M are each titrated with a strong base, which will require the greatest volume of base to reach the equivalence point? (A) Acid 1 (B) Acid 2 (C) Acid 3 (D) All the acids will require the same volume of base to reach the equivalence point.

D. All the acids will require the same volume of base to reach the equivalence point.

In the diagram above, which of the labeled arrows identifies hydrogen bonding in water? (A) A (B) B (C) C (D) D

D. D

A kinetics experiment is set up to collect the gas that is generated when a sample of chalk, consisting primarily of solid CaCO3 , is added to a solution of ethanoic acid, CH3COOH. The rate of reaction between CaCO3 and CH3COOH is determined by measuring the volume of gas generated at 25∞C and 1 atm as a function of time. Which of the following experimental conditions is most likely to increase the rate of gas production? (A) Decreasing the volume of ethanoic acid solution used in the experiment (B) Decreasing the concentration of the ethanoic acid solution used in the experiment (C) Decreasing the temperature at which the experiment is performed (D) Decreasing the particle size of the CaCO3 by grinding it into a fine powder

D. Decreasing the particle size of the CaCO3 by grinding it into a fine powder

The photoelectron spectra above show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum? (A) Nitrogen atoms have a half-filled p subshell. (B) There are more electron-electron repulsions in oxygen atoms than in nitrogen atoms. (C) Electrons in the p subshell of oxygen atoms provide more shielding than electrons in the p subshell of nitrogen atoms. (D) Nitrogen atoms have a smaller nuclear charge than oxygen atoms.

D. Nitrogen atoms have a smaller nuclear charge than oxygen atoms.

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, ΔH, for each step? (A) All three steps are exothermic. (B) All three steps are endothermic. (C) Steps 1 and 2 are exothermic, and the final step is endothermic. (D) Steps 1 and 2 are endothermic, and the final step is exothermic.

D. Steps 1 and 2 are endothermic, and the final step is exothermic.

2 NO(g) + O2(g) Æ 2 NO2(g) Consider the following mechanism for the reaction represented above. Step 1: 2 NO ¨Æ N2O2 (fast reversible) Step 2: N2O2 + O2 Æ 2 NO2 (slow) Which of the following statements is true? (A) Step 1 represents a unimolecular reaction. (B) Increasing the concentration of NO will decrease the overall rate of the reaction. (C) Raising the temperature will have no effect on the numerical value of the rate constant. (D) The rate law that is consistent with the mechanism is rate = k[NO]2 [O2].

D. The rate law that is consistent with the mechanism is rate = k[NO]2 [O2].

Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are (A) the same because the molecular formulas are similar (B) the same because C and S have similar electronegativity values (C) different because the lone pair of electrons on the S atom make it the negative end of a dipole (D) different because S has a greater number of electron domains (regions of electron density) surrounding it than C has

D. different because S has a greater number of electron domains (regions of electron density) surrounding it than C has

Container A B C Gas Methane Ethane Butane Formula CH4 C2H6 C4H10 Molar mass (g/mol) 16 30. 58 Temperature (∞C) 27 27 27 Pressure (atm) 2.0 4.0 2.0 The average kinetic energy of the gas molecules is (A) greatest in container A (B) greatest in container B (C) greatest in container C (D) the same in all three containers

D. the same in all three containers