Chem AP Classroom Midterm Review

The table above shows the results from a rate study of the reaction X + Y → Z. Starting with known concentrations of X and Y in experiment 1, the rate of formation of Z was measured. If the reaction was first order with respect to X and second order with respect to Y, the initial rate of formation of Z in experiment 2 would be Responses A R/4 B R/2 C R D 2R

D 2R

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

D 1.0 M

Which of the following best explains what happens as photons of visible light are absorbed by dye molecules? Responses 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.

PCl3,Cl2,CaCl2 Which of the following correctly ranks the substances listed above in order of increasing ionic character in their bonding? Responses A Cl2, PCl3, CaCl2 B Cl2, CaCl2, PCl3 C CaCl2, PCl3, Cl2 D CaCl2, Cl2,

A Cl2, PCl3, CaCl2

Which of the diagrams above best represents the interactions that are responsible for the relatively large solubility of KCl crystals in water, and why? Responses 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.

(A) H2O(B) NH3(C) BH3(D) CH4(E) SiH4 Has two lone pairs of electrons Responses A H2O B NH3 C BH3 D CH4 E SiH4

A H2O

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? Responses A HCl and CH3NH2 B HCl and NH3 C HBr and CH3NH2 D HBr and NH3

A HCl and CH3NH2

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? Responses A HS− B CH3COO− C H3O+ D

A HS−

Which of the following best explains why more energy is required for the process occurring at 110 K than for the process occurring at 90 K ? Responses A Intermolecular attractions are completely overcome during vaporization. B Intermolecular attractions in the solid phase are weaker than in the liquid phase. C Electron clouds of methane molecules are less polarizable at lower temperatures. D Vaporization involves a large increase in temperature.

A Intermolecular attractions are completely overcome during vaporization.

A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance? Responses A Ionic bonds B Metallic bonds C Covalent bonds D Hydrogen bonds

A Ionic bonds

2Mg(s)+SiCl4(l)→2MgCl2(s)+Si(s) Which of the following statements about the reaction represented above is correct? Responses 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? Responses A It is less because more HC2H3O2(aq) reacted with the base. B It is the same because the 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(��) is a proton donor.

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

The enthalpy of vaporization of water is 40.7 kJ/mol. Which of the following best explains why the enthalpy of vaporization of methane is less than that of water? Responses A Methane does not exhibit hydrogen bonding, but water does. B Methane has weaker dispersion forces. C Methane has a smaller molar mass. D Methane has a much lower density.

A Methane does not exhibit hydrogen bonding, but water does.

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? Responses 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.

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? Responses 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.

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? Responses 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? Responses 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 h

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

Bi⁢ 83214→Po 84214+�−1 0 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? (� = the number of moles in the sample) Responses A nBi B nPo C ln(nBi) D 1/nBi

A nBi

The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points? Responses A Butane < 1-propanol < acetone B Butane < acetone < 1-propanol C 1-propanol < acetone < butane D Acetone = butane < 1-propanol

B Butane < acetone < 1-propanol

Equimolar samples of CH4(�) and C2H6(�) are in identical containers at the same temperature. The C2H6(�) deviates much more from ideal behavior than the CH4(�) does. Which of the following best helps explain this deviation? Responses 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.

The melting point of MgO is higher than that of NaF. Explanations for this observation include which of the following? I. Mg2+ is more positively charged than Na+. II. O2- is more negatively charged than F-. III. The O2- ion is smaller than the F- ion. Responses A II only B I and II only C I and III only D II and III only E I, II, and III

B I and II only

The diagram above best illustrates which of the following phenomena associated with solids that have metallic bonding? Responses 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.

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? Responses 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.

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? Responses A NH3(aq)+HCl(aq)→NH4Cl(aq) B NH3(aq)+H+(aq)→NH4+(aq) C NH3(aq)+HCl(aq)→NH4+(aq)+Cl−(aq) D

B NH3(aq)+H+(aq)→NH4+(aq)

Resonance is most commonly used to describe the bonding in molecules of which of the following? Responses A CO2 B O3 C H2O D CH4 E SF6

B O3

For which of the following molecules are resonance structures necessary to describe the bonding satisfactorily? Responses A H2S B SO2 C CO2 D OF2 E PF3

B SO2

Which of the following claims about a binary compound composed of elements with the same electronegativity is most likely to be true? Responses 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.

A student measures the absorbance of a solution containing FeSCN2+ ions 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? Responses 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.

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? Responses 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.

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? Responses 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.

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(�), which causes a precipitate of BaSO4(�) to form, as represented by the equation above. The student filters the BaSO4(�), 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?

A jar labeled NaCl contains a powder. 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? Responses A Mass B Mass percent of Na C Density D Color

B. Mass percent of Na

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? Responses 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?

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

C 109.5°

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? Responses A 9×10−21J B 4×10−20J C 4×10−19J D

C 4×10−19J

When students added 2.0g of NaI crystals to 100.mL of Pb(NO3)2(��), 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? Responses A A physical change occurred when a new yellow compound was formed. B A physical change occurred when the color of the NaI 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.

The question refers to the following species. (A) H2O(B) NH3(C) BH3(D) CH4(E) SiH4 Has a central atom with less than an octet of electrons Responses A H2O B NH3 C BH3 D CH4 E SiH4

C BH3

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? Responses 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.

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C2H6O, molecules? Responses 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.

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 59oC and 184oC, respectively? Responses 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.

The lattice energy of a salt is related to the energy required to separate the ions. For which of the following pairs of ions is the energy that is required to separate the ions largest? (Assume that the distance between the ions in each pair is equal to the sum of the ionic radii.) Responses A Na+(g) and Cl−(g) B Cs+(g) and Br−(g) C Mg2+(g) and O2−(g) D Ca2+(g) and O2−(g)

C Mg2+(g) and O2−(g)

Step 1. N2H2O2 ⇄ N2HO2- + H+ (fast equilibrium) Step 2. N2HO2- → N2O + OH- (slow) Step 3. H+ + OH- → H2O (fast) Nitramide, N2H2O2, decomposes slowly in aqueous solution. This decomposition is believed to occur according to the reaction mechanism above. The rate law for the decomposition of nitramide that is consistent with this mechanism is given by which of the following? Responses A Rate = k[N2H2O2] B Rate = k[N2H2O2] [H+] C Rate = k[N2H2O2]/[H+] D Rate = k[N2H2O2][N2HO2] E Rate = k[N2H2O2] [OH-]

C Rate = k[N2H2O2]/[H+]

Which of the following substances is a strong electrolyte when dissolved in water? Responses A Sucrose B Ethanol C Sodium nitrate D Acetic acid E Ammonia

C Sodium nitrate

ElementNPAsSbBiAtomic Radius (picometers)65 100 115 145 160 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? Responses 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.

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? Responses A The C-F is easier to break than the C-H bond. B The C-F 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.

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

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? Responses 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.

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? Responses 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.

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? Responses 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.

Which of the following best helps explain why the first ionization energy of K is less than that of Ca? Responses 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.

Which of the following Lewis diagrams represents a molecule that is polar? A. BF3 B. CO2 C. CH2Cl2 D. N2

C. CH2Cl2

5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) At a certain time during the titration, the rate of appearance of O2(g) was 1.0 x 10-3 mol/(L⋅s). What was the rate of disappearance of MnO4- at the same time? Responses A 6.0 x 10-3 mol/(L⋅s) B 4.0 x 10-3 mol/(L⋅s) C 6.0 x 10-4 mol/(L⋅s) D 4.0 x 10-4 mol/(L⋅s)

D 4.0 x 10-4 mol/(L⋅s)

In which of the following processes are covalent bonds broken? Responses A I2(s) → I2(g) B CO2(s) → CO2(g) C NaCl(s) → NaCl(l) D C(diamond) → C(g) E Fe(s) → Fe(l)

D C(diamond) → C(g)

In which of the following liquids do the intermolecular forces include dipole-dipole forces? Responses A F2(l) B CH4(l) C CF4(l) D CH2F2(l)

D CH2F2(l)

The gases CO2(�) and NH3(�) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(�) can be liquefied at a lower pressure than CO2(�) can be liquefied. Which of the following is the best justification for this claim? Responses 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

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.

The crystal structure of NaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(�) to molten NaBr(�) in terms of electrical conductivity? Responses 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

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.

Which of the following is the correct net ionic equation of the neutralization reaction between hydrofluoric acid and sodium hydroxide in aqueous solution? Responses 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)

The energy diagram for the reaction X + Y → Z is shown above. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences? Responses A I only B II only C III only D I and II only

D I and II only

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? Responses 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.

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? Responses 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.

CCl4(�) deviates more from ideal gas behavior than C�4(�) does. Which of the following statements best explains this observation? Responses A The mass of the CCl4 molecule is greater than that of the CH4 molecule. B The bond energy of the C-Cl bond is greater than that of the C-H bond. C The dipole-dipole forces between CCl4 molecules are greater than those between CH4 molecules. D The London dispersion forces between CCl4 molecules are stronger than those between CH4 molecules.

D The London dispersion forces between CCl4 molecules are stronger than those between CH4 molecules.

The table above shows the melting points of MgO(s) and NaF(s). Which of the following best helps explain why the melting point of MgO(s) is much higher than that of NaF(s) ? Responses A The mass of F− ions is greater than that of O2− ions. B The mass of Mg2+ ions is greater than that of Na+ ions. C The difference between the electronegativity values of Mg and O is smaller than the difference between the values of Na and F. D The charges of Mg2+ and O2− ions are greater than those of Na+ and F− ions.

D The charges of Mg2+ and O2− ions are greater than those of Na+ and F− ions.

Which of the following best helps to explain why the atomic radius of K is greater than that of Br? Responses 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? Responses 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.

The structural formulas for two isomers of 1,2-dichloroethene are shown above. Which of the two liquids has the higher equilibrium vapor pressure at 20°C, and why? Responses A The cis-isomer, because it has dipole-dipole interactions, whereas the trans-isomer has only London dispersion forces B The cis-isomer, because it has only London dispersion forces, whereas the trans-isomer also has dipole-dipole interactions C The trans-isomer, because it has dipole-dipole interactions, whereas the cis-isomer has only London dispersion forces D The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

D The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

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(�) ? Responses 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.

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? Responses 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?

C2H4(g) + H2(g) →platinum C2H6(g) C2H4(g) is reduced by H2(g) in the presence of a solid platinum catalyst, as represented by the equation above. Factors that could affect the rate of the reaction include which of the following? Changes in the partial pressure of H2(g) Changes in the particle size of the platinum catalyst Changes in the temperature of the reaction system Responses A III only B I and II only C I and III only D II and III only E I, II, and III

E I, II, and III

Which of the following compounds contains both ionic and covalent bonds? Responses A SO3 B C2H5OH C MgF2 D H2S E NH4Cl

E NH4Cl

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 degrees 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