AP Chem: AP Classroom MCA

image #18 Which of the Lewis diagrams shown above is the more likely structure of CO2, and why? A.) Diagram 1, because all the atoms have a formal charge of 0. B.) Diagram 1, because double bonds are stronger than triple bonds. C.) Diagram 2, because all the atoms have a formal charge of 0. D.) Diagram 2, because triple bonds are stronger than double bonds.

A.) Diagram 1, because all the atoms have a formal charge of 0.

image #42 The absorption spectrum of a certain red dye is shown above. If a student analyzing the same concentration of this dye neglected to wipe fingerprints off the cuvette before placing it in the spectrophotometer, how would the absorption curve be affected? A.) The peak of the curve would be higher because more light would be absorbed. B.) The peak of curve would be lower because less light would be absorbed. C.) The peak of the curve would be shifted to the left because less light would be absorbed. D.) The peak of the curve would be shifted to the right because more light would be absorbed.

A.) The peak of the curve would be higher because more light would be absorbed.

image #3 Based on the mass spectrum of a pure element represented above, the average atomic mass of the element is closest to which of the following? A.)185.7 amu B.) 186.0 amu C.) 186.3 amu D.) 186.9 amu

C.) 186.3 amu

Which of the following best helps explain why the first ionization energy of K is less than that of Ca? A.) The electronegativity of K is greater than that of Ca. B.) The atomic radius of the K atom is less than that of the Ca atom. C.) The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca. D.) The nucleus of the K atom has fewer neutrons, on average, than the nucleus of the Ca atom has.

C.) The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca.

2X+Y2→X2Y2 A chemist is studying the reaction between the gaseous chemical species X and Y2, represented by the equation above. Initial rates of reaction are measured at various concentrations of reactants. The results are recorded in the following table. image #47 A second chemist repeated the three experiments and observed that the reaction rates were considerably greater than those measured by the first chemist even though the concentrations of the reactants and the temperature in the laboratory were the same as they were for the first chemist. Which of the following is the best pairing of a claim about a most likely cause for the greater rates measured by the second chemist and a valid justification for that claim? A.) The pressures of the gases used by the second chemist must have been lower than those used by the first chemist, thus the collisions between reacting particles were less frequent than they were in the first chemist's experiments. B.) The pressures of the gases used by the second chemist must have been lower than those used by the first chemist, thus the number of collisions with sufficient energy to cause reaction was lower than it was in the first chemist's experiments. C.) The second chemist must have added a catalyst for the reaction, thus providing a different reaction pathway for the reactant particles to react with an activation energy that was lower than that of the uncatalyzed reaction in the first chemist's experiments. D.) The second chemist must have added a catalyst for the reaction, thus providing energy to reactant particles to increase their rate of reaction compared to their rate of reaction in the first chemist's experiments.

C.) The second chemist must have added a catalyst for the reaction, thus providing a different reaction pathway for the reactant particles to react with an activation energy that was lower than that of the uncatalyzed reaction in the first chemist's experiments.

image #16 Which of the diagrams above best represents the CH2O molecule, and why? A.) Diagram 1, because all bond angles are 180°. B.) Diagram 1, because all atoms have a formal charge of 0. C.) Diagram 2, because the molecule has a trigonal pyramidal shape. D.) Diagram 2, because all atoms have a formal charge of 0.

D.) Diagram 2, because all atoms have a formal charge of 0.

On the basis of electronegativity differences between atoms, which of the following scientific claims is the most accurate regarding the bonding in Mg(NO3)2(s) ? A.) There is polar covalent bonding between Mg atoms and N atoms. B.) There is polar covalent bonding between Mg atoms and O atoms. C.) There is ionic bonding between N5+ ions and O2− ions. D.) There is ionic bonding between Mg2+ ions and NO3− ions.

D.) There is ionic bonding between Mg2+ ions and NO3− ions.

image #53 Which of the following best describes the elementary step(s) in the reaction mechanism represented in the diagram above? A.) One step: 2X(g)+Y(g)→X2Y(g) B.) One step: X2(g)+Y(g)→X2Y(g) C.) Two steps: Step 1:X(g)+Y(g)→XY(g) Step 2:X(g)+XY(g)→X2Y(g) D.) Two steps: Step 1: 2X(g)→X2(g) Step 2: X2(g)+Y(g)→X2Y(g)

D.) Two steps: Step 1: 2X(g)→X2(g) Step 2: X2(g)+Y(g)→X2Y(g)

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Assume that 50.0mL of 1.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined. According to the balanced equation, if 50.0mL of 2.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined, the amount of precipitate formed would A.) double, because all of the coefficients are 1 B.) double, because the amount of one of the reactants was doubled C.) not change, because all of the coefficients are 1 D.) not change, because the amount of AgNO3(aq) did not change

D.) not change, because the amount of AgNO3(aq) did not change

image #38 Which of the diagrams above best represents the interactions that are responsible for the relatively large solubility of KCl crystals in water, and why? A.) Diagram 1, because strong ion-dipole interactions between KCl and water help to dissociate the solute. B.) Diagram 1, because strong London dispersion forces between the K+ and Cl− ions and water replace the weak London dispersion forces between two water molecules. C.) Diagram 2, because strong dipole-dipole forces between KCl and water help to separate the KCl units within the crystals. D.) Diagram 2, because the hydrogen bonds between water molecules expand to accommodate the KCl particles and pull them into solution.

A.) Diagram 1, because strong ion-dipole interactions between KCl and water help to dissociate the solute.

Step 1: HCOOH + H2SO4→HCOOH2+ +HSO4− Step 2: HCOOH2+→HCO+ + H2O Step 3: HCO+ + HSO4−→CO + H2SO4 The elementary steps in a proposed mechanism for the decomposition of HCOOH are represented above. Which of the following identifies the catalyst in the overall reaction and correctly justifies the choice? A.) H2SO4, because it is consumed in the first step of the mechanism and regenerated in a later step. B.) HCOOH, because increasing the concentration of HCOOH increases the reaction rate. C.) HCOOH2+, because it is produced in the first step of the mechanism and consumed in a later step. D.) CO, because it is produced in the final step of the reaction mechanism.

A.) H2SO4, because it is consumed in the first step of the mechanism and regenerated in a later step.

2Mg(s)+SiCl4(l)→2MgCl2(s)+Si(s) Which of the following statements about the reaction represented above is correct? A.) It is an oxidation-reduction reaction, and Mg is oxidized. B.) It is an oxidation-reduction reaction, and electrons are transferred from SiCl4 to Mg C.) It is an oxidation-reduction reaction, and the oxidation number of Cl changes from +4 to +2. D.) It is not an oxidation-reduction reaction because none of the oxidation numbers change.

A.) It is an oxidation-reduction reaction, and Mg is oxidized.

HC2H3O2(aq)+OH−(aq)→C2H3O2−(aq)+H2O(l) A student carried out a titration using HC2H3O2(aq) and NaOH(aq). The net ionic equation for the neutralization reaction that occurs during the titration is represented above. The NaOH(aq) was added from a buret to the HC2H3O2(aq) in a flask. The equivalence point was reached when a total of 20.0mL of NaOH(aq) had been added to the flask. How does the amount of HC2H3O2(aq) in the flask after the addition of 5.0mL of NaOH(aq) compare to the amount of HC2H3O2(aq) in the flask after the addition of 1.0mL of NaOH(aq), and what is the reason for this result? A.) It is less because more HC2H3O2(aq) reacted with the base. B.) It is the same because the half-equivalence point has not been reached. C.) It is the same because all of the coefficients in the neutralization equation are 1. D.) It is greater because HC2H3O2(aq) is a proton donor.

A.) It is less because more HC2H3O2(aq) reacted with the base.

2X+Y2→X2Y2 A chemist is studying the reaction between the gaseous chemical species X and Y2, represented by the equation above. Initial rates of reaction are measured at various concentrations of reactants. The results are recorded in the following table. image #45 Given the information in the table above, which of the following is the experimental rate law? A.) Rate=k[X][Y2] B.) Rate=k[X]2[Y2] C.) Rate=k[X][Y2]2 D.) Rate=k[X]2[Y2]2

A.) Rate=k[X][Y2]

Reaction A: O+O→O2 Reaction B: C2H4+C2H4→C4H8 Reaction C: CO+O2→CO2+O Reaction D: CH3I+Br−→CH3Br+I− The equations shown above represent four elementary reactions. Which of the following identifies the reaction in which the number of successful collisions and reaction rate are independent of the orientation of the reactants and explains why? A.) Reaction A, because the electron clouds of the O atoms are distributed symmetrically. B.) Reaction B, because each C2H4 molecule has a double bond. C.) Reaction C, because both CO and O2 are linear molecules. D.) Reaction D, because the reactant Br− and the product I− are negatively charged.

A.) Reaction A, because the electron clouds of the O atoms are distributed symmetrically.

image #39 The infrared spectrum above represents the absorption of certain wavelengths of radiation by molecules of CO2. Which of the following best explains what occurs at the molecular level as the CO2 molecules absorb photons of the infrared radiation? A.) The atoms in the CO2 molecules increase their vibration as the bonds between the atoms bend and stretch. B.) The molecules of CO2 increase the energy of their rotational motions. C.) The electrons in the valence shells of the atoms in the CO2 molecules are promoted to higher electronic energy levels. D.) The bonds between the atoms in the CO2 molecules are continuously broken and then re-form.

A.) The atoms in the CO2 molecules increase their vibration as the bonds between the atoms bend and stretch.

image #20 Which of the following correctly compares the strength of the two carbon-to-carbon bonds in the molecule represented in the Lewis diagram shown above? A.) The carbon-to-carbon bond on the left is stronger because it is a double bond. B.)The carbon-to-carbon bonds are the same strength because the C-C-C bond angle is 180°. C.) The carbon-to-carbon bonds are the same strength because they are both bonds between carbon atoms. D.) The carbon-to-carbon bond on the right is stronger because there are more hydrogen atoms attached to the rightmost carbon atom than to the leftmost carbon atom.

A.) The carbon-to-carbon bond on the left is stronger because it is a double bond.

image #37 A student adds a 1g sample of an unknown, brittle solid to distilled water, stirs the mixture, and then measures its conductivity. The student repeats this procedure with more samples of the unknown solid and then produces the graph above. Which of the following statements about the graph and the properties of the solid is correct? A.) The increase in conductivity indicates that the unknown is an ionic solid that dissociates into ions when it dissolves in water. B.) The increase in conductivity indicates that the unknown is a network covalent solid that ionizes in water. C.) The straight line plot indicates that the unknown solid is infinitely soluble in water. D.) The straight line plot indicates that the unknown solid has a very low solubility in water.

A.) The increase in conductivity indicates that the unknown is an ionic solid that dissociates into ions when it dissolves in water.

A student uses a spectrophotometer to analyze a solution of blue food dye. The student first rinses a cuvette with distilled water. Then the student adds the blue dye solution to the cuvette, forgetting to rinse the cuvette with the blue dye solution first. The student places the cuvette in the spectrophotometer and measures the absorbance of the solution. Assuming that some distilled water droplets were still in the cuvette when the blue dye solution was added, how would the measured absorbance be affected? A.) The measured absorbance would be too low, because the distilled water left in the cuvette would slightly dilute the solution. B.) The measured absorbance would be too low, because the distilled water would change the optimum wavelength of absorbance. C.) The measured absorbance would be too high, because the water would allow more light to pass through the cuvette. D.) The measured absorbance would be too high, because the distilled water would also absorb some light.

A.) The measured absorbance would be too low, because the distilled water left in the cuvette would slightly dilute the solution.

image #28 Two sealed, rigid 5.0L containers each contain a gas at the same temperature but at a different pressure, as shown above. Also shown are the results of transferring the entire contents of container 1 to container 2. No gases escape during the transfer. Assuming ideal behavior, which statement is correct regarding the total pressure of the gases after they are combined? A.) The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant. B.) The total pressure of the gases in the mixture is lower than the sum of the initial pressures of oxygen and nitrogen because some of the energy of the particles will be lost due to an increase in the number of collisions. C.) The total pressure of the gases in the mixture is higher than the sum of the initial pressures of oxygen and nitrogen because of the intermolecular forces that develop between oxygen and nitrogen molecules. D.) The total pressure of the gases in the mixture cannot be determined because the actual value of the temperature is not given.

A.) The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant.

5Fe2+(aq)+MnO4−(aq)+8H+(aq)→5Fe3+(aq)+Mn2+(aq)+4H2O(l) Which of the following represents the oxidation half-reaction based on the balanced ionic equation shown above? A.) Fe2+(aq)+e−→Fe3+(aq) B.) Fe2+(aq)→Fe3+(aq)+e− C.) MnO4−(aq)→Mn2+(aq)+5e− D.) MnO4−(aq)+5e−→Mn2+(aq)

B.) Fe2+(aq)→Fe3+(aq)+e−

image #13 Which of the following indicates whether the solid substance represented by the particulate diagram shown above conducts electricity and explains why or why not? A.) It conducts electricity because it is made of positive and negative particles. B.) It conducts electricity because electrons are free to move through the substance. C.) It does not conduct electricity because electrons are strongly attracted to specific positive particles. D.) It does not conduct electricity because the positive particles are not free to move through the substance.

B.) It conducts electricity because electrons are free to move through the substance.

image #10 Molten (liquid) NaCl is represented by the particulate diagram shown above. Which of the following indicates whether NaCl(l) conducts electricity and best explains why or why not? A.) It conducts electricity because Na is a metal. B.) It conducts electricity because ions are free to move. C.) It does not conduct electricity because Cl is a nonmetal. D.) It does not conduct electricity because there are no free electrons.

B.) It conducts electricity because ions are free to move.

image #43 Which of the following best describes the process represented above that takes place when NH3 is added to water? A.) It is a single replacement reaction in which an electron pair on N is replaced with an H atom. B.) It is an acid-base reaction in which a proton is exchanged from H2O to NH3. C.) It is a precipitation reaction in which NH4OH, an insoluble solid, is produced. D.) It is an oxidation-reduction reaction in which the oxidation number of NN changes from −3 to −4.

B.) It is an acid-base reaction in which a proton is exchanged from H2O to NH3.

image #15 The diagram above best illustrates which of the following phenomena associated with solids that have metallic bonding? A.) Electrical conductivity, because it shows a lattice of positive ions immersed in a sea of electrons. B.) Malleability, because it shows how adjacent layers of positive ions can move relative to one another while remaining in full contact with the electron sea. C.) Heat conductivity, because it shows how layers of atoms can slide past one another, creating friction between layers and causing the temperature of the solid to increase. D.) The ability to form substitutional alloys, because it shows how atoms of two different metals can combine in a one-to-one ratio.

B.) Malleability, because it shows how adjacent layers of positive ions can move relative to one another while remaining in full contact with the electron sea.

image #23 The diagram above represents four cations, all shown to the same scale. Which cation would be predicted by Coulomb's law to have the strongest ion-dipole attraction to water, and why? A.) Li+ , because it is the smallest group 1 metal ion. B.) Mg2+ , because it has the largest charge-to-size ratio. C.) Na+ , because it has the smallest charge-to-size ratio. D.) Ca2+ , because it is the largest group 2 metal ion.

B.) Mg2+ , because it has the largest charge-to-size ratio.

image #6 The complete photoelectron spectrum of an element is given above. Which labeled peak corresponds to the 1s electrons and why? A.) Peak X, because 1s electrons are the easiest to remove from the atom. B.) Peak X, because 1s electrons have the strongest attractions to the nucleus. C.) Peak Y, because electrons in the 1s sublevel are the farthest from the nucleus. D.) Peak Y, because there are fewer electrons in an s sublevel than in a p sublevel.

B.) Peak X, because 1s electrons have the strongest attractions to the nucleus.

image #40 One type of organic molecule can be converted to another type of organic molecule through an oxidation-reduction process, as represented in the diagram above. Which of the following best explains why infrared spectroscopy is an appropriate method to confirm that the product contains a carbonyl? A.) The absorption of infrared radiation causes the nonbonding electrons on oxygen to transition into a higher electronic energy level. B.) The absorption of infrared radiation leads to an increase in molecular vibrational level associated with the stretching of the carbonyl. C.) The absorption of infrared radiation causes the electrons in the pi bond to transition to a higher bonding energy level. D.) Infrared radiation leads to an increase in the molecular rotational level associated with the carbonyl as the axis of rotation.

B.) The absorption of infrared radiation leads to an increase in molecular vibrational level associated with the stretching of the carbonyl.

A student measures the absorbance of a solution containing FeSCN2+ ion using a spectrophotometer. The cuvette used by the student has two frosted walls and two transparent walls. The student properly orients the cuvette so that the path of the light goes through the transparent sides of the cuvette when calibrating the spectrophotometer. How will the measured absorbance of the FeSCN2+ be affected if the student incorrectly orients the cuvette so that the path of the light is through the frosted sides of the cuvette? A.) The measured absorbance of the FeSCN2+ solution will not be affected. B.) The measured absorbance of the FeSCN2+ solution will be higher than the actual absorbance. C.) The measured absorbance of the FeSCN2+ solution will be lower than the actual absorbance. D.) The effect on the measured absorbance of the FeSCN2+ solution depends on the concentration of the FeSCN2+ solution.

B.) The measured absorbance of the FeSCN2+ solution will be higher than the actual absorbance.

image #7 The photoelectron spectrum for the element boron is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom? A.) The spectrum shows an odd number electrons. B.) The spectrum shows a single electron in the 2p subshell. C.) The spectrum shows equal numbers of electrons in the first and second electron shells. D.) The spectrum shows three electrons with the same binding energy in the second electron shell.

B.) The spectrum shows a single electron in the 2p subshell.

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment? A.) What is the density of M? B.) What is the molar mass of M? C.) What is the melting point of M? D.) What is the melting point of MO?

B.) What is the molar mass of M?

Which of the following is the correct electron configuration for a ground-state atom of magnesium (atomic number 12) ? A.) 1s2 2s2 2p8 B.) 1s2 2s2 3s2 3p6 C.) 1s2 2s2 2p6 3s2 D.) 1s2 2s2 3s4 3p4

C.) 1s2 2s2 2p6 3s2

Al(s)→Al3+(aq)+3e− Sn2+(aq)+2e−→Sn(s) Based on the half-reactions represented above, which of the following is the balanced ionic equation for the oxidation-reduction reaction between Al(s) and Sn2+(aq) ? A.) Al(s)+Sn2+(aq)→Al3+(aq)+Sn(s)+e− B.) 3Al(s)+2Sn2+(aq)→3Al3+(aq)+2Sn(s) C.) 2Al(s)+3Sn2+(aq)→2Al3+(aq)+3Sn(s) D.) Al(s)+Sn2+(aq)+2e−→Al3+(aq)+Sn(s)+3e−

C.) 2Al(s)+3Sn2+(aq)→2Al3+(aq)+3Sn(s)

image #41 The frequency and energy ranges of photons in some parts of the electromagnetic spectrum are given in the table above. Which of the following could be the energy of a photon in the visible range? A.) 9×10−21J B.) 4×10−20J C.) 4×10−19J D.) 9×10−19J

C.) 4×10−19J

Mass of NaI crystals- 2.0g Color of NaI crystals- White Color of solid recovered- Yellow Color of filtered solution- Colorless Mass of dry solid recovered- 3.0g When students added 2.0g of NaI crystals to 100.mL of Pb(NO3)2(aq), a yellow precipitate formed. After the solution was filtered, the yellow solid was dried and weighed. Data from the experiment are shown in the table above. Which of the following claims is best supported by the observations? A.) A physical change occurred when a new yellow compound was formed. B.) A physical change occurred when the color of theNaI solid added changed to yellow when mixed with water. C.) A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed. D.) A chemical change occurred when covalent bonds between the yellow solid and water were broken during drying.

C.) A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed.

image #22 Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C2H6O, molecules? A.) Diagram 1, because it shows hydrogen bonds forming between hydrogen atoms from different ethanol molecules. B.) Diagram 1, because it shows strong, directional dipole-dipole forces between two polar ethanol molecules. C.) Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule. D.) Diagram 2, because it shows the dipole from an ethanol molecule inducing a dipole in another ethanol molecule.

C.) Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule.

image #30 The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct? A.) The molecules of gas Z have a higher average kinetic energy than the molecules of gas X. B.) There are fewer molecules in the sample of gas Z than in the sample of gas X. C.) Gas Z has a smaller molar mass than gas X. D.) Gas Z has a greater molar mass than gas X.

C.) Gas Z has a smaller molar mass than gas X.

C12H22O11(aq)+H2O(l)→2C6H12O6(aq) The chemical equation shown above represents the hydrolysis of sucrose. Under certain conditions, the rate is directly proportional to the concentration of sucrose. Which statement supports how a change in conditions can increase the rate of this reaction? A.) Increasing the amount of water in which the sugar is dissolved will increase the frequency of collisions between the sucrose molecules and the water molecules resulting in an increase in the rate of hydrolysis. B.) Decreasing the temperature will increase the frequency of the collisions between the sucrose molecules and the water molecules resulting in an increase in the rate of hydrolysis. C.) Increasing the concentration of sucrose will increase the rate of hydrolysis by increasing the frequency of the collisions between the sucrose and the water molecules. D.) Decreasing the concentration of sucrose will increase the rate of hydrolysis by increasing the frequency of the collisions between the sucrose and the water molecules.

C.) Increasing the concentration of sucrose will increase the rate of hydrolysis by increasing the frequency of the collisions between the sucrose and the water molecules.

A chemistry teacher carried out several demonstrations, and students recorded their observations. For one of the demonstrations, a student concluded that a physical change took place, but not a chemical change. Which of the following observations could the student have made of the results of the demonstration? A.) Two colorless solutions were combined, and the resulting solution was pink. B.) When a solid was added to a liquid, sparks were produced. C.) One piece of solid substance was changed into small pieces. D.) When two solutions were combined, a precipitate formed.

C.) One piece of solid substance was changed into small pieces.

image #35 The diagram above shows thin-layer chromatograms of the same mixture of two compounds. Based on the chromatograms, which solvent would be most effective at separating the two compounds if the same stationary phase is used for column chromatography? A.) Solvent A B.) Solvent B C.) Solvent C D.) Solvent D

C.) Solvent C

CH3I+NaOH→CH3OH+NaI The rate of the reaction represented by the chemical equation shown above is expressed as rate=k[CH3I][NaOH]. Based on this information, which of the following claims is correct? A.) The reaction will proceed at a slower rate with increasing temperature. B.) The rate of the reaction will double when the concentrations of both CH3I and NaOH are doubled. C.) The rate of the reaction will double if the concentration of CH3I is doubled while keeping the concentration of NaOH constant. D.) A larger amount of CH3OH will be produced if the concentrations of CH3I and NaOH are halved.

C.) The rate of the reaction will double if the concentration of CH3I is doubled while keeping the concentration of NaOH constant.

Step 1: 2NO⇄(NO)2 (fast) Step 2: (NO)2+O2⇄2NO2 (slow) The elementary steps in a proposed mechanism for the reaction 2 NO(g)+O2(g)→2NO2(g) are represented by the equations above. Which of the following is the rate law for the overall reaction that is consistent with the proposed mechanism? A.) rate=k[NO]2 B.) rate=k[NO][O2] C.) rate=k[NO]^2[O2] D.) rate=k[(NO)2][O2]

C.) rate=k[NO]^2[O2]

Step 1: 2X(g)⇄X2(g) (fast) Step 2: X2(g)+Y(g)→X2Y(g) (slow) The rate law for the hypothetical reaction 2X(g)+Y(g)→X2Y(g) is consistent with the mechanism shown above. Which of the following mathematical equations provides a rate law that is consistent with this mechanism? A.) rate=k[X]^2 B.) rate=k[X2][Y] C.) rate=k[X]^2[Y] D.) rate=k[2X][Y]

C.) rate=k[X]^2[Y]

image #52 The diagram above shows the distribution of molecular energies for equimolar samples of a reactant at different temperatures. Based on the diagram, at which temperature will the reactant be consumed at the fastest rate, and why? A.) At T1, because a larger fraction of the molecules have about the same energy. B.) At T2, because at this temperature most of the molecules undergo collisions frequently. C.) At T3, because at this temperature the rate of consumption for about half of the molecules is determined by their orientation. D.) At T4, because a larger fraction of the molecules have an energy that is equal to or greater than the activation energy.

D.) At T4, because a larger fraction of the molecules have an energy that is equal to or greater than the activation energy.

The gases CO2(g) and NH3(g) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(g) can be liquefied at a lower pressure than CO2(g) can be liquefied. Which of the following is the best justification for this claim? A.) At 20°C, the average speed of NH3 molecules is greater than that of CO2 molecules because NH3 molecules have less mass than CO2 molecules have. B.) CO2 is a nonpolar molecule that has no significant intermolecular forces, whereas NH3 has strong London dispersion intermolecular forces. C.) Both CO2 and NH3 are nonpolar molecules that have only London dispersion intermolecular forces, but the larger electron cloud of CO2 molecules causes it to have stronger intermolecular forces. D.) CO2 is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH3 molecules.

D.) CO2 is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH3 molecules.

image #26 The crystal structure of NaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(s) to molten NaBr(l) in terms of electrical conductivity? A.) Crystalline NaBr contains no freely moving electrons that could conduct an electrical current, whereas electrons can flow freely in molten NaBr, which is a good conductor of electricity. B.) Crystalline NaBr and molten NaBr both contain ions that are held in fixed positions due to strong electrostatic attractions among the ions, making neither a good electrical conductor. C.) Crystalline NaBr and molten NaBr both contain Na atoms that transfer electrons to Br atoms in a chemical reaction, thus allowing them both to be good conductors of electricity. D.) Crystalline NaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.

D.) Crystalline NaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.

image #56 The diagram above shows the reaction energy profiles for a reaction with and without a catalyst. Which of the following identifies the reaction energy profile for the catalyzed reaction, and why? A.) Profile X, because a catalyst minimizes the number of elementary steps required for a reaction to proceed. B.) Profile X, because the activation energy for the reverse reaction is greater than for the forward reaction, which increases its rate. C.) Profile Y, because an increase in the number of transition states increases the rate of the reaction. D.) Profile Y, because it introduces a different reaction path that reduces the activation energy.

D.) Profile Y, because it introduces a different reaction path that reduces the activation energy.

image #33 The graph above shows how a particular real gas deviates from ideal behavior at very high pressures. Based on this information, which of the following is most likely the gas and gives the reason based on kinetic molecular theory? A.) H2, because it has the smallest mass. B.) N2, because its molecules have a triple bond. C.) Ne, because it has a completely filled valence shell. D.) SO2, because it has the largest molecular volume.

D.) SO2, because it has the largest molecular volume.

Which of the following best helps to explain why the atomic radius of K is greater than that of Br? A.) The first ionization energy of K is higher than that of Br. B.) The valence electrons in K are in a higher principal energy level than those of Br. C.) In the ground state, an atom of K has fewer unpaired electrons than an atom of Br has. D.) The effective nuclear charge experienced by valence electrons is smaller for K than for Br.

D.) The effective nuclear charge experienced by valence electrons is smaller for K than for Br.

Which of the following claims about a binary compound in which the bonding is ionic is most likely to be scientifically valid? A.) Both elements in the compound are metals. B.) The atomic masses of the elements in the compound are relatively small. C.) There is equal sharing of electrons between the atoms of the elements in the compound. D.) The electronegativity difference between the elements in the compound is relatively large.

D.) The electronegativity difference between the elements in the compound is relatively large.

Based on formal charges, which of the following is the best Lewis electron-dot diagram for H3NO? image #17

A.)

Which of the following particulate-level diagrams best represents an interstitial alloy? image #14

A.)

In a lab a student is given a 21g sample of pure Cu metal. Which of the following pieces of information is most useful for determining the number of Cu atoms in the sample? Assume that the pressure and temperature in the lab are 1.0 atm and 25°C. A.) The molar mass of Cu B.) The density of Cu at 25°C C.) The volume of the Cu sample D.) The ratio of the two main isotopes found in pure Cu

A.) The molar mass of Cu

image #44 In the reaction between C5H5N(aq) and HCl(aq) represented above, C5H5N acts as A.) a Brønsted-Lowry base B.) a Brønsted-Lowry acid C.) the conjugate base of HCl D.) the conjugate acid of [C5H5NH]+

A.) a Brønsted-Lowry base

image #8 The complete photoelectron spectrum of the element carbon is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom? A.) The spectrum shows four electrons in the inner electron shell. B.) The spectrum shows equal numbers of electrons in the three occupied electron subshells. C.) The spectrum shows that all the electrons in the valence shell have the same binding energy. D.) The spectrum shows more electrons in the inner electron shell than in the outer electron shell.

B.) The spectrum shows equal numbers of electrons in the three occupied electron subshells.

Which of the following Lewis diagrams represents a molecule that is polar? image #19

C.)

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is evidence that ionic bonds formed during the precipitation? A.) The resulting solution is colorless. B.) The resulting solution conducts electricity. C.) The precipitate has a high melting point. D.) The temperature of the solution did not change significantly during the precipitation.

C.) The precipitate has a high melting point.

A 1.0mol sample of which of the following compounds has the greatest mass? A.) NO B.) NO2 C.) N2O D.) N2O5

D.) N2O5

The particles in solid KI, a stable ionic compound, are arranged to maximize coulombic attractions while minimizing coulombic repulsions among the particles. Which of the following diagrams best represents the structure of solid KI? image #12

A.)

1s2 2s2 2p6 3s2 3p6 How many unpaired electrons are in the atom represented by the electron configuration above? A.) 0 B.) 11 C.) 22 D.) 33

A.) 0

In an experiment on the photoelectric effect, a photon with a frequency of 7×10^14s−1 was absorbed by a sample. What is the approximate energy of this photon? A.) 5×10−19J B.) 1×10−15J C.) 2×106J D.) 1×1048J

A.) 5×10−19J

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is the balanced net ionic equation for the formation of the precipitate? A.) Ag+(aq)+Cl−(aq)→AgCl(s) B.) Na+(aq)+NO3−(aq)→NaNO3(s) C.) NaCl(aq)+AgNO3(aq)→NaNO3(s)+AgCl(aq) D.) NaCl(aq)+AgNO3(aq)→NaNO3(aq)+AgCl(s)

A.) Ag+(aq)+Cl−(aq)→AgCl(s)

Na2CO3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g) A student combined two colorless aqueous solutions. One of the solutions contained Na2CO3 as the solute and the other contained HCl. The chemical reaction that took place is represented by the equation above. What experimental result would be evidence that a chemical reaction took place when the solutions were combined? A.) Bubbles formed when the two solutions were combined. B.) The total volume of the mixture is close to the sum of the initial volumes. C.) The resulting solution is colorless. D.) The resulting solution conducts electricity.

A.) Bubbles formed when the two solutions were combined.

Which of the following best explains what happens as photons of visible light are absorbed by dye molecules? A.) Certain electrons in the dye molecule move to a higher energy level, with the difference in energy between the lower and higher energy levels being the same as the energy of the absorbed photons. B.) Certain chemical bonds in the dye molecules begin to bend and stretch, with the difference in energy between the lower and higher vibrational states being the same as the energy of the absorbed photons. C.) The dye molecules begin to rotate faster in certain modes, with the difference in energy between the lower and higher rotational states being the same as the energy of the absorbed photons. D.) Certain covalent bonds in the dye molecules begin to break and re-form, with the bond energies of the bonds being the same as the energy of the absorbed photons.

A.) Certain electrons in the dye molecule move to a higher energy level, with the difference in energy between the lower and higher energy levels being the same as the energy of the absorbed photons.

Based on the Brønsted-Lowry theory of acids and bases, which of the following species can act as both a conjugate acid and a conjugate base? A.) HS− B.) CH3COO− C.) H3O+ D. )NH4+

A.) HS−

At 10.°C, 20.g of oxygen gas exerts a pressure of 2.1atm in a rigid, 7.0L cylinder. Assuming ideal behavior, if the temperature of the gas was raised to 40.°C, which statement indicates the new pressure and explains why? A.) 1.9 atm, because the pressure P decreases by the proportion 283313283313. B.) 2.3atm, because the pressure P increases by the proportion 313/283. C.) 0.52 atm, because the pressure P decreases by the proportion 10./40. D.) 8.4 atm, because the pressure P increases by the proportion 40./10.

B.) 2.3atm, because the pressure P increases by the proportion 313/283.

Which of the following numerical expressions gives the number of moles in 5.0g of CaO? A.) 5.0g × 56g/mol B.) 5.0g / 56g/mol C.) 56g/mol / 5.0g D.) 1 / 5.0g × 1 / 56g/mol

B.) 5.0g / 56g/mol

image #1 The mass spectrum for an unknown element is shown above. According to the information in the spectrum, the atomic mass of the unknown element is closest to A.) 90 amu B.) 91 amu C.) 93 amu D.) 94 amu

B.) 91 amu

A gaseous air‑fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air‑fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air‑fuel mixture? A.) About 0.083 atm, because the initial volume of the gas mixture was 12 times larger than its final volume. B.) About 12 atm, because the volume of the gas mixture decreased by a factor of 12. C.) About 120.atm, because the initial volume of the gas mixture was 120 times larger than its final volume. D.) About 550.atm, because the change in the volume of the gas mixture was 550.mL.

B.) About 12 atm, because the volume of the gas mixture decreased by a factor of 12.

image #11 The particulate-level diagram shown above best helps to explain which of the following properties of ionic solids? A.) Density B.) Brittleness C.) Malleability D.) Conductivity

B.) Brittleness

Step 1:2NO2(g)→NO3(g)+NO(g) (slow) Step 2:NO3(g)+CO(g)→NO2(g)+CO2(g) (fast) A proposed two-step mechanism for the chemical reaction NO2(g)+CO(g)→NO(g)+CO2(g) is shown above. Which of the following equations is a correct rate law that is consistent with the elementary steps in the mechanism? A.) Rate=k[NO2] B.) Rate=k[NO2]2 C.) Rate⁢=k[NO3][CO] D.) Rate=k[NO2][CO]

B.) Rate=k[NO2]2

Which of the following claims about a binary compound composed of elements with the same electronegativity is most likely to be true? A.) The compound has properties similar to those of both elements. B.) The bonding in the compound is nonpolar covalent. C.) The boiling point of the compound is above 1000°C. D.) The compound contains strong ionic bonds.

B.) The bonding in the compound is nonpolar covalent.

Methanol, CH3OH, dissolves completely in water to form a solution that does not conduct electricity. Which of the following diagrams best shows the major type of attractive force that exists between the particles in the solution? image #36

C.)

Which of the following represents the electron configuration of an oxygen atom in the ground state? image #5

C.)

image #31 The diagram above shows the distribution of speeds for a sample of O2(g). Which of the following graphs shows the distribution of speeds for the same sample at a higher temperature (dashed line) ?

C.)

What volume of a 0.100MHCl stock solution should be used to prepare 250.00mL of 0.0250MHCl? A.) 1.00mL B.) 16.0mL C.) 62.5mL D.) 100.mL

C.) 62.5mL

K2SO3(aq)+2HNO3(aq)→2KNO3(aq)+SO2(g)+H2O(l) According to the balanced chemical equation above, when 100.0mL of 0.100MK2SO3(aq) is mixed with 100.0mL of 0.200MHNO3(aq) at 30°C and 1 atm, the volume of SO2 gas produced is 0.24 L. If it is assumed that the reaction goes to completion, which of the the following changes would double the volume of SO2 produced at the same temperature and pressure? (For each change, assume that the other solutions and volumes remain the same.) A.) Using 200.0mL of the 0.100MK2SO3(aq), because it then becomes the reactant in excess B.) Using 200.0mL of the 0.200MHNO3(aq), because the volume of SO2 produced is inversely proportional to the number of moles at constant temperature and pressure C.) Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because these are the required stoichiometric amounts D.) Using 400.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because this provides the same number of moles of each reactant

C.) Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because these are the required stoichiometric amounts

214^/83 Bi → 214^/84 Po + 0^/1 e− Bismuth-214 undergoes first-order radioactive decay to polonium-214 by the release of a beta particle, as represented by the nuclear equation above. Which of the following quantities plotted versus time will produce a straight line? A.) [Bi] B.) [Po] C.) ln[Bi] D.) 1/[Bi]

C.) ln[Bi]

image #55 The proposed mechanism for a reaction involves the three elementary steps represented by the particle models shown above. On the basis of this information, which of the following models represents an intermediate in the overall reaction?

D.)

A 500.mL aqueous solution of Na3PO4 (molar mass=164g/mol) was prepared using 82g of the solute. What is the molarity of Na3PO4 in the resulting solution? A.) 0.0010M B.) 0.16M C.) 0.25M D.) 1.0M

D.) 1.0M

How many grams of NaCl (molarmass=58g/mol) are needed to prepare 100.mL of a 0.25M NaCl solution? A.) 0.23g B.) 0.43⁢g C.) 0.67g D.) 1.5g

D.) 1.5g

Electromagnetic radiation with a maximum wavelength of 540nm (5.4×10−7 m ) is needed for the study of the photoelectric effect in potassium atoms. What is the approximate frequency that corresponds to this wavelength? A.) 1.8×10−15s−1 B.) 1.6×102s−1 C.) 1.9×106s−1 D.) 5.6×1014s−1

D.) 5.6×1014s−1

Zn(s)+2 HCl(aq)→ZnCl2(aq)+H2(g) Zn(s) reacts with HCl(aq) according to the equation shown above. In trial 1 of a kinetics experiment, a 5.0g piece of Zn(s) is added to 100mL of 0.10MHCl(aq). The rate of reaction between Zn(s) and HCl(aq) is determined by measuring the volume of H2(g) produced over time. In trial 2 of the experiment, 5.0g of powdered Zn(s) is added to 100mL of 0.10MHCl(aq). Which trial will have a faster initial rate of reaction and why? A.) Trial 1, because there is a higher concentration of Zn(s) in the reaction mixture. B.) Trial 1, because the sample of Zn(s) has less surface area for the reaction to take place. C.) Trial 2, because there is a higher concentration of HCl(aq) in the reaction mixture. D.) Trial 2, because the sample of Zn(s) has a greater surface area for the reaction to take place.

D.) Trial 2, because the sample of Zn(s) has a greater surface area for the reaction to take place.

The catalyzed decomposition of NH3(g) at high temperature is represented by the equation above. The rate of disappearance of NH3(g) was measured over time for two different initial concentrations of NH3(g) at a constant temperature. The data are plotted in the graph below. image #50 On the basis of the data in the graph, which of the following best represents the rate law for the catalyzed decomposition of NH3(g) ? A.) Rate=k B.) Rate=k[NH3] C.) Rate=k[NH3]2 D.) Rate=k[N2][H2]

A.) Rate=k

O3(g)+O(g)→2O2(g) The decomposition of O3 occurs according to the balanced equation above. In the presence of NO, the decomposition proceeds in two elementary steps, as represented by the following mechanism. Step 1:O3+NO→NO2+O2 (slow) Step 2:NO2+O→NO+O2 (fast) Based on the information, which of the following is the rate law? A.) Rate=k[O3][NO] B.) Rate=k[NO2][O2] C.) Rate=k[NO2][O] D.) Rate=k[NO][O]

A.) Rate=k[O3][NO]

image #54 The diagram above shows the progress of the chemical reaction for the synthesis of ammonia from its elements. The adsorption of the N2 molecules on the surface of Ru weakens the triple bond between the two N atoms. Based on the diagram, what is the role of Ru in this process? A.) Ru is a catalyst. B.) Ru is a reactant. C.) Ru is a product. D.) Ru is an intermediate.

A.) Ru is a catalyst.

Step 1: ? (slow) Step 2: NO2(g)+F(g)→NO2F(g) (fast) Overall: 2 NO2(g)+F2(g)→2NO2F(g) The overall reaction represented above is proposed to take place through two elementary steps. Which of the following statements about the chemical equation for step 1 and the rate law for the overall reaction is correct? A.) The chemical equation for step 1 is NO2(g)+F2(g)→NO2F(g)+F(g), and the rate law for the overall reaction is rate=k[NO2][F2]. B.) The chemical equation for step 1 is NO2(g)+F(g)→NO2F(g)+F2(g), and the rate law for the overall reaction is rate=k[NO2][F]. C.) The chemical equation for step 1 is 2NO2(g)+F2(g)→2NO2F(g), and the rate law for the overall reaction is rate=k[NO2][F]. D.) The chemical equation for step 1 is 3NO2(g)+F2(g)+F(g)→3NO2F(g), and the rate law for the overall reaction is rate=k[NO2]2[F2].

A.) The chemical equation for step 1 is NO2(g)+F2(g)→NO2F(g)+F(g), and the rate law for the overall reaction is rate=k[NO2][F2].

A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture? A.) The molar mass of each gas B.) The density of the gases in the vessel C.) The total pressure of the gases in the vessel D.) The number of atoms per molecule for each gas

A.) The molar mass of each gas

image #51 The two diagrams above represent collisions that take place at the same temperature between a CO molecule and an NO2 molecule. The products are CO2 and NO. Which diagram most likely represents an effective collision, and why? A.) Diagram 1 represents an effective collision because the molecules have about the same size and the same energy, which leads to a larger rate constant (k). B.) Diagram 1 represents an effective collision because the two molecules have the proper orientation to form a new C−O bond as long as they possess enough energy to overcome the activation energy barrier. C.) Diagram 2 represents an effective collision because the molecules are aligned head-to-head and that maximizes the overlap between their atomic orbitals, forming more products. D.) Diagram 2 represents an effective collision because the oxygen atoms are the most electronegative and will minimize their repulsions when oriented away from each other.

B.) Diagram 1 represents an effective collision because the two molecules have the proper orientation to form a new C−O bond as long as they possess enough energy to overcome the activation energy barrier.

image #34 When methanol and water are mixed together, they form a homogeneous mixture. Based on the information in the table above, which of the following would be the best procedure for separating a mixture of methanol and water? A.) Filtration B.) Distillation C.) Paper chromatography D.) Column chromatography

B.) Distillation

2N2O5(g)→4NO2(g)+O2(g) For the reaction represented by the equation above, the concentration of N2O5 was measured over time. The following graphs were created using the data. image #49 Based on the graphs above, what is the order of the reaction with respect to N2O5 ? A.) Zeroth order B.) First order C.) Second order D.) Third order

B.) First order

Step 1: N2O5→NO2+NO3 (slow) Step 2: NO2+NO3→NO2+NO+O2 (fast) Step 3: NO+N2O5→3 NO2( fast) A proposed reaction mechanism for the decomposition of N2O5(g) is shown above. Based on the proposed mechanism, which of the following correctly identifies both the chemical equation and the rate law for the overall reaction? A.) The chemical equation for the overall reaction is NO(g)+N2O5(g)→3NO2(g), and the rate law is rate=k[NO][N2O5]. B.) The chemical equation for the overall reaction is 2N2O5(g)→4NO2(g)+O2(g), and the rate law is rate=k[N2O5]. C.) The chemical equation for the overall reaction is 2N2O5(g)→4NO2(g)+O2(g), and the rate law is rate=k[N2O5]2. D.) The chemical equation for the overall reaction is N2O5(g)+NO(g)+NO3(g)→4NO2(g)+O2(g), and the rate law is rate=k[N2O5][NO][NO3].

B.) The chemical equation for the overall reaction is 2N2O5(g)→4NO2(g)+O2(g), and the rate law is rate=k[N2O5].

image #21 Based on the Lewis diagram for NH3, shown above, the H-N-H bond angle is closest to which of the following? A.) 60° B.) 90° C.) 109.5° D.) 120°

C.) 109.5°

2X+Y2→X2Y2 A chemist is studying the reaction between the gaseous chemical species X and Y2, represented by the equation above. Initial rates of reaction are measured at various concentrations of reactants. The results are recorded in the following table. image #46 Based on the information above, determine the initial rate of disappearance of X in experiment 1. A.) 16M/s B.) 32M/s C.) 64M/s D.) 128M/s

C.) 64M/s

mass- 27.3 g mass percent of Na- 35.2% density- 2.05 g cm^-3 color- white The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl? A.) Mass B.) Mass percent of NaNa C.) Density D.) Color

C.) Density

H2(g)+I2(g)→2HI(g) For the reaction between H2 and I2, shown above, the following two-step reaction mechanism is proposed. Step 1: I2 ⇄ 2I (fast equilibrium) Step 2: H2+2I → 2HI (slow) What is the rate law expression for this reaction if the second step is rate determining? A.) Rate=k[I2] B.) Rate=k[H2][I]^2 C.) Rate=k[H2][I2] D.) Rate=k[I2][I]^2

C.) Rate=k[H2][I2]

Step 1: H2O2+I−→IO−+H2O Step 2: H2O2+IO−→H2O+O2+I− The mechanism for a chemical reaction is shown above. Which of the following statements about the overall reaction and rate laws of the elementary reactions is correct? A.) The chemical equation for the overall reaction is 2 H2O2+I−→ 2 H2O+O2+I−, and the rate law for elementary step 2 is rate=k[H2O2][IO−]. B.) The chemical equation for the overall reaction is H2O2+IO−→ H2O+O2+I−, and the rate law for elementary step 2 is rate=k[H2O2]2[IO−]. C.) The chemical equation for the overall reaction is 2 H2O2→2 H2O+O2, and the rate law for elementary step 1 is rate=k[H2O2][I−]. D.) The chemical equation for the overall reaction is 2 H2O2→2 H2O+O2, and the rate law for elementary step 1 is rate=k[H2O2]2.

C.) The chemical equation for the overall reaction is 2 H2O2→2 H2O+O2, and the rate law for elementary step 1 is rate=k[H2O2][I−].

Step 1: H2+IBr→HI+HBr (slow) Step 2: HI+IBr→I2+HBr (fast) A proposed mechanism for the reaction H2+2IBr→I2+2HBr is shown above. Two experiments were performed at the same temperature but with different initial concentrations. Based on this information, which of the following statements is correct? A.) The rate of the reaction will undergo a 4-fold increase in the experiment in which the initial concentrations of both HI and IBr were doubled. B.) The rate of the reaction will undergo a 2-fold increase in the experiment in which the initial concentrations of both HI and IBr were doubled. C.) The rate of the reaction will undergo a 4-fold increase in the experiment in which the initial concentrations of both H2 and IBr were doubled. D.) The rate of the reaction will undergo a 8-fold increase in the experiment in which the initial concentrations of both H2 and IBr were doubled.

C.) The rate of the reaction will undergo a 4-fold increase in the experiment in which the initial concentrations of both H2 and IBr were doubled.

A beaker was half filled with freshly distilled H2O and placed on a hot plate. As the temperature of the water reached 100°C, vigorous bubbling was observed in the beaker. The gaseous contents of the bubbles were analyzed. The presence of which of the following substances would support the claim that the observed phenomenon was a physical change? A.) H2(g) B.) O2(g) C.) CO2(g) D.) H2O(g

D.) H2O(g)

Which of the following is the correct net ionic equation of the neutralization reaction between hydrofluoric acid and sodium hydroxide in aqueous solution? A.) HF(aq)+NaOH(aq)→H2O(l)+NaF(aq) B.) HF(aq)+NaOH(aq)→NaH(aq)+FOH(aq) C.) H+(aq)+OH−(aq)→H2O(l) D.) HF(aq)+OH−(aq)→H2O(l)+F−(aq)

D.) HF(aq)+OH−(aq)→H2O(l)+F−(aq)

Which of the following best helps explain why an atom of Rb gas more easily loses an electron in a chemical reaction than an atom of Li gas? A.) Rb has a higher electronegativity than Li has. B.) The Rb atom has a greater number of valence electrons than the Li atom has. C.) The nucleus of the Rb atom has a greater number of protons and neutrons than the nucleus of the Li atom has. D.) In the Rb atom the valence electron is farther from its nucleus than the valence electron of Li is from its nucleus.

D.) In the Rb atom the valence electron is farther from its nucleus than the valence electron of Li is from its nucleus.

Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When the reaction represented above proceeds, heat is produced. Which of the following best describes the reaction? A.) It is a combustion reaction because heat is produced by the reaction. B.) It is a double replacement reaction because 2Cl atoms are added to Zn. C.) It is an acid-base reaction because HCl is an acid that is capable of exchanging H+. D.) It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced.

D.) It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced.

Rb reacts with O in a mole ratio of 2 to 1, forming the ionic compound Rb2O. Which of the following elements will react with O in a mole ratio of 2 to 1, forming an ionic compound, and why? A.) S, because it is in the same group as O. B.) Cs, because it is in the same group as Rb. C.) Sr, because it is in the same period as Rb. D.) Br, because the atomic mass of Br is similar to that of Rb.

B.) Cs, because it is in the same group as Rb.

image #2 The mass spectrum represented above is most consistent with which of the following elements? A.) Eu B.) Gd C.) Tb D.) Dy

B.) Gd

Ba2+(aq)+SO42−(aq)→BaSO4(s) A student obtains a 10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment? A.) Is the Na2SO4(s) used in the experiment pure? B.) Is the BaCl2(s) used in the experiment pure? C.) What is the molar solubility of BaCl2 in water? D.) What is the molar solubility of BaSO4 in water?

B.) Is the BaCl2(s) used in the experiment pure?

image #27 The structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite? A.) Diamond contains covalent bonds, whereas graphite contains ionic bonds. B.) Diamond contains ionic bonds, whereas graphite contains covalent bonds. C.) Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces. D.) Carbon atoms in diamond have a sea of mobile electrons that make the structure strong, whereas graphite does not contain delocalized electrons.

C.) Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces.

image #29 The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why? A.) Diagram 1, because all the particles have the same speed. B.) Diagram 1, because the particles are moving in different directions. C.) Diagram 2, because the particles have a net kinetic energy of zero. D.) Diagram 2, because the particles have a variety of different speeds.

D.) Diagram 2, because the particles have a variety of different speeds.

Zn(s)+CuSO4(aq)→Cu(s)+ZnSO4(aq) When a zinc plate is placed in an aqueous solution of copper sulfate, elemental copper forms, as represented by the equation above. Which of the following represents the reduction half-reaction of the reaction? A.) Cu2+(aq)+2e−→Cu(s) B.) Cu(s)→Cu2+(aq)+2e− C.) Zn(s)+2e−→Zn2−(aq) D.) Zn(s)→Zn2+(aq)+2e−

A.) Cu2+(aq)+2e−→Cu(s)

A student was given two clear liquids; a colorless liquid and a dark-blue liquid. The student was asked to combine the liquids in a beaker and record observations. Which of the following results, if true, would provide the best evidence that a chemical change took place when the liquids were combined? A.) The resulting mixture was cloudy. B.) The total volume of the mixture was equal to the sum of the initial volumes. C.) The resulting liquid was light blue. D.) The liquids formed two separate layers in the beaker.

A.) The resulting mixture was cloudy.

image #25 The diagrams above represent two allotropes of solid phosphorus. Which of the following correctly identifies the allotrope with the higher melting point and explains why? A.) Allotrope I, because it has P4 molecules with covalent bonds that are stronger than dispersion forces between individual PP atoms in allotrope II. B.) Allotrope II, because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P4 molecules in allotrope I. C.) Allotrope II, because it has metallic bonding that is stronger than the covalent bonding found in the P4 molecules in allotrope I. D.) Both allotropes have the same melting point because they both contain phosphorous atoms.

B.) Allotrope II, because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P4 molecules in allotrope I.

Equimolar samples of CH4(g) and C2H6(g) are in identical containers at the same temperature. The C2H6(g) deviates much more from ideal behavior than the CH4(g) does. Which of thefollowing best helps explain this deviation? A.) C2H6 molecules have more hydrogen bonding than CH4 molecules do. B.) C2H6 molecules have a larger, more polarizable electron cloud than CH4 molecules do. C.) The C2H6 molecules have a greater average kinetic energy than the CH4 molecules have. D.) The C2H6 molecules have a greater average speed than the CH4 molecules have.

B.) C2H6 molecules have a larger, more polarizable electron cloud than CH4 molecules do.

C6H5COOH(aq)+NaOH(aq)→C6H5COONa(aq)+H2O(l) Which of the following identifies a conjugate acid-base pair in the reaction represented above? A.) C6H5COOH and OH− B.) C6H5COOH and C6H5COO− C.) OH− and H2O D. ) OH− and C6H5COO−

B.) C6H5COOH and C6H5COO−

Which of the following is the correct net ionic equation of the reaction that occurs when aqueous solutions of ammonia and hydrochloric acid are combined? A.) NH3(aq)+HCl(aq)→NH4Cl(aq) B.) NH3(aq)+H+(aq)→NH4+(aq) C.) NH3(aq)+HCl(aq)→NH4+(aq)+Cl−(aq) D.) NH3(aq)+H+(aq)+Cl−(aq)→NH4+(aq)+Cl−(aq)

B.) NH3(aq)+H+(aq)→NH4+(aq)

2NO(g)+2H2(g)→N2(g)+2H2O(g) image #48 The information in the data table above represents two different trials for an experiment to study the rate of the reaction between NO(g) and H2(g), as represented by the balanced equation above the table. Which of the following statements provides the correct explanation for why the initial rate of formation of N2 is greater in trial 2 than in trial 1 ? Assume that each trial is carried out at the same constant temperature. A.) The activation energy of the reaction is smaller in trial 2 than it is in trial 1. B.) The frequency of collisions between reactant molecules is greater in trial 2 than it is in trial 1. C.) The value of the rate constant for the reaction is smaller in trial 2 than it is in trial 1. D.) The value of the rate constant for the reaction is greater in trial 2 than it is in trial 1.

B.) The frequency of collisions between reactant molecules is greater in trial 2 than it is in trial 1.

A student obtains a mixture of the chlorides of two unknown metals, X and Z. The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XCl(s) and of ZCl(s) in the mixture? A.) The number of isotopes of Cl B.) The molar masses of X and Z C.) The density of either XCl(s) or ZCl(s) D.) The percent by mass of Cl in the mixture

B.) The molar masses of X and Z

What charge does Al typically have in ionic compounds, and why? A.) +1, because in the ground state it has one unpaired electron. B.) +2, because it has two electrons in the 2s2s subshell. C.) +3, because it has three valence electrons. D.) +4, because it is in the fourth row of the periodic table.

C.) +3, because it has three valence electrons.

image #9 The atomic radii of the elements in the nitrogen group in the periodic table are given in the table above. Which of the following best helps explain the trend of increasing atomic radius from N to Bi? A.) The number of particles in the nucleus of the atom increases. B.) The number of electrons in the outermost shell of the atom increases. C.) The attractive force between the valence electrons and the nuclei of the atoms decreases. D.) The repulsive force between the valence electrons and the electrons in the inner shells decreases.

C.) The attractive force between the valence electrons and the nuclei of the atoms decreases.

image #24 A solid compound of a group 1 (alkali) metal and a group 17 (halogen) element dissolves in water. The diagram above represents one type of solute particle present in the solution. Which of the following identifies the solute particle and best helps explain how the solute particle interacts with water molecules? A.) The particle is a negative ion, and the interactions are hydrogen bonds. B.) The particle is a negative ion, and the interactions are ion-dipole attractions. C.) The particle is a positive ion, and the interactions are ion-dipole attractions. D.) The particle is a positive ion, and the interactions are dipole-dipole attractions.

C.) The particle is a positive ion, and the interactions are ion-dipole attractions.

Which of the following methods is most appropriate to use to determine the number of different-colored components in a sample of black ink? A.) Distillation at atmospheric pressure B.) Elemental analysis to determine the mass ratio of C:H:N:O C.) Column chromatography using a nonpolar stationary phase and water as the mobile phase D.) Paper chromatography using different solvents with a range of polarities as the mobile phase

D.) Paper chromatography using different solvents with a range of polarities as the mobile phase

A 42.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 36.0g of C and 6.0g of H. Which of the following questions about the compound can be answered using the results of the analysis? A.) What was the volume of the sample? B.) What is the molar mass of the compound? C.) What is the chemical stability of the compound? D.) What is the empirical formula of the compound?

D.) What is the empirical formula of the compound?