AP Chemistry Unit 3

3.10-3.13 unit

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3.5 to 3.9 unit

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How many grams of CaCl2 (molar mass =111g/mol) are needed to prepare 100.mL of 0.100MCl−(aq) ions? A 0.555g0.555g B 1.11g1.11g C 2.22g2.22g D 5.55g5.55g

A

The diagram above represents the absorption spectrum for a pure molecular substance. Which of the following correctly indicates the type of transition observed for the substance in each of the regions of the absorption spectrum?

region x - electronic transition region y - molecular vibration region z - molecular rotation

Which statement correctly compares what occurs when molecules absorb photons in the microwave region with what occurs when molecules absorb photons in the infrared region? A Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states. B Microwave photons cause electrons in the molecules to increase their electronic energy states, whereas infrared photons cause the molecules to increase their rotational energy states. C Microwave photons cause the molecules to increase their vibrational energy states, whereas infrared photons cause electrons in the molecules to increase their electronic energy states. D Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause electrons in the molecules to increase their electronic energy states.

A

Based on Coulomb's Law and the information in the table above, which of the following cations is most likely to have the weakest interaction with an adjacent water molecule in an aqueous solution? A Li+ B Na+ C Ca2+ D In3+

C

Beta-carotene is an organic compound with an orange color. The diagram above shows the ultraviolet spectrum of beta-carotene. Which of the following statements is true about the absorption bands in the spectrum? A The absorption band between 250250 and 320 nm320 ⁢⁢nm is due to transitions in electronic energy levels, and the absorption band between 380380 and 520 nm520 nm is due to transitions in molecular vibrational levels. B The absorption band between 250250 and 320 nm320 nm is due to transitions in molecular vibrational levels, and the absorption band between 380380 and 520 nm520 nm is due to transitions in molecular rotational levels. C The two main absorption bands are associated with transitions in electronic energy levels. The band in the region corresponding to shorter wavelengths shows a lower absorbance than the band in the region corresponding to longer wavelengths. D The two main absorption bands are associated with transitions in molecular vibrational levels. The band in the region corresponding to shorter wavelengths shows a lower absorbance than the band in the region corresponding to longer wavelengths.

C

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

D

The dimerization of NO2(g) , an exothermic process, is represented by the equation above. Which of the following experimental techniques will allow the most accurate determination of the concentration of NO2(g) at equilibrium? A Paper chromatography B Gravimetric analysis C Titration D Spectrophotometry

D

The volume of distilled water that should be added to 10.0 mL of 6.00 M HCl(aq) in order to prepare a 0.500 M HCl(aq) solution is approximately A 50.0 mL B 60.0 mL C 100. ML D 110. ML E 120. mL

D

A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs? A Ethyl acetate, because it has fewer C-C bonds to break B Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces C Butyl acetate, because it has more C-C bonds to break D Butyl acetate, because it has a longer carbon chain and weaker dipole-dipole attractions

B

Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why? A Ne, because its atoms have the largest radius B HF, because its molecules form hydrogen bonds C C2H6 , because each molecule can form multiple hydrogen bonds D CH4 , because its molecules have the greatest London dispersion forces

B

Of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why? A 0.1MHC2H3O2(aq)0.1MHC2H3O2(aq) because its molecules have the most atoms. B 0.1MKI(aq)0.1MKI(aq) because KIKI completely dissociates in water to produce ions. C 0.1MCH3OH(aq)0.1MCH3OH(aq) because its molecules can form hydrogen bonds. D All three solutions have the same electrical conductivity because the concentrations are the same.

B

The diagram above represents a particle in aqueous solution. Which of the following statements about the particle is correct? A The particle must be a cation because the negative end of each water molecule is pointed toward it. B The particle must be an anion because the positive end of each water molecule is pointed toward it. C The charge of the particle cannot be determined because water molecules have no net charge. D The charge of the particle cannot be determined because the water molecules are arranged symmetrically and their partial charges cancel.

B

When a sample of oxygen gas in a closed container of constant volume is heated until its absolute temperature is doubled, which of the following is also doubled? A The density of the gas B The pressure of the gas C The average velocity of the gas molecules D The number of molecules per cm3 E The potential energy of the molecules

B

Which of the following could be the identity of a white crystalline solid that exhibits the following properties? It melts at 320°C. It does not conduct electricity as a solid. It conducts electricity in an aqueous solution. A C6H12O6(s) B NaOH(s) C SiO2(s) D Cu(s)

B

A 0.20 mol sample of MgCl2(s) and a 0.10 mol sample of KCl(s) are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution? A 0.15 M B 0.30 M C 0.50 M D 0.60 M E 1.0 M

E

Sodium chloride is LEAST soluble in which of the following liquids? A H2O B CCl4 C HF D CH3OH E CH3COOH

B

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water? A CH4 B CCl4 C NH3 D PH3

C

A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. The temperature is kept constant. Which of the following statements about combining the gases is correct? A The average speed of the helium atoms increases when the gases are combined. B The average speed of the neon atoms increases when the gases are combined. C The average kinetic energy of the helium atoms increases when the gases are combined. D The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.

D

An equimolar mixture of N2(g) and Ar(g) is kept inside a rigid container at a constant temperature of 300 K. The initial partial pressure of Ar in the mixture is 0.75atm. An additional amount of Ar was added to the container, enough to double the number of moles of Ar gas in the mixture. Assuming ideal behavior, what is the final pressure of the gas mixture after the addition of the Ar gas? A 0.75atm0.75atm, because increasing the partial pressure of ArAr decreases the partial pressure of N2N2. B 1.13atm1.13atm, because 33%33% of the moles of gas are N2N2. C 1.50atm1.50atm, because the number of moles of N2N2 did not change. D 2.25atm2.25atm, because doubling the number of moles of ArAr doubles its partial pressure.

D

Based on the structural formulas, which of the following identifies the compound that is more soluble in water and best helps to explain why? A Ethane, because the electron clouds of its molecules are more polarizable than those of propanol. B Ethane, because its molecules can fit into the spaces between water molecules more easily than those of propanol can. C Propanol, because its molecules have a greater mass than the molecules of ethane have. D Propanol, because its molecules can form hydrogen bonds with water molecules but those of ethane cannot.

D

Benzene, C6H6 , has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best describes the intermolecular forces of attraction between water and benzene? A Benzene is nonpolar, therefore there are no forces between water and benzene. B The H atoms in benzene form hydrogen bonds with the O atoms in water. C Benzene is hydrophobic, therefore there is a net repulsion between water and benzene. D There are dipole-induced dipole and London dispersion interactions between water and benzene.

D

In a paper chromatography experiment, a sample of a pigment is separated into two components, X and Y, as shown in the figure above. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results? A X has a larger molar mass than Y does. B Y has a larger molar mass than X does. C X is more polar than Y. D Y is more polar than X.

D

Using a spectrophotometer, a student measures the absorbance of four solutions of CuSO4 at a given wavelength. The collected data is given in the table above. Which of the following is the most likely explanation for the discrepant data in trial 4 ? A The solution was at a lower temperature than the solutions in the other trials. B The measurement was made using a different spectrophotometer that uses a cell with a longer path length. C The solution was saturated and the flow of light through the solution was restricted. D The concentration of the solution was actually lower than 0.150M0.150M.

D

Which of the following techniques is most appropriate for the recovery of solid KNO3 from an aqueous solution of KNO3? A Paper chromatography B Filtration C Titration D Electrolysis E Evaporation to dryness

E

A student is given a sample of a pure, white crystalline substance. Which of the following would be most useful in providing data to determine if the substance is an ionic compound? A Examining the crystals of the substance under a microscope B Determining the density of the substance C Testing the electrical conductivity of the crystals D Testing the electrical conductivity of an aqueous solution of the substance

D

If 200. mL of 0.60 M MgCl2(aq) is added to 400. mL of distilled water, what is the concentration of Mg2+(aq) in the resulting solution? (Assume volumes are additive). A 0.20 M B 0.30 M C 0.40 M D 0.60 M E 1.2 M

A

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

A

A 2 L sample of N2(g) and a 1 L sample of Ar(g), each originally at 1 atm and 0°C, are combined in a 1 L tank. If the temperature is held constant, what is the total pressure of the gases in the tank? A 1 atm B 2 atm C 3 atm D 4 atm E 5 atm

C

A gas mixture at 0°C and 1.0atm contains 0.010mol of H2, 0.015mol of O2, and 0.025mol of N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture? A About 0.010atm0.010atm, because there is 0.010mol0.010mol of H2H2 in the sample. B About 0.050atm0.050atm, because there is 0.050mol0.050mol of gases at 0°C0°C and 1.0atm1.0atm. C About 0.20atm0.20atm, because H2H2 comprises 20%20% of the total number of moles of gas. D About 0.40atm0.40atm, because the mole ratio of H2:O2:N2H2:O2:N2 is 0.4:0.6:10.4:0.6:1.

C

A rigid metal tank contains oxygen gas. Which of the following applies to the gas in the tank when additional oxygen is added at constant temperature? A The volume of the gas increases. B The pressure of the gas decreases. C The average speed of the gas molecules remains the same. D The total number of gas molecules remains the same. E The average distance between the gas molecules increases.

C

A sample of an ideal gas is cooled from 50.0oC to 25.0oC in a sealed container of constant volume. Which of the following values for the gas will decrease? I. The average molecular mass of the gas II. The average distance between the molecules III. The average speed of the molecules A I only B II only C III only D I and III E II and III

C

A 0.10 M aqueous solution of sodium sulfate, Na2SO4 , is a better conductor of electricity than a 0.10 M aqueous solution of sodium chloride, NaCl. Which of the following best explains this observation? A Na2SO4 is more soluble in water than NaCl is. B Na2SO4 has a higher molar mass than NaCl has. C To prepare a given volume of 0.10 M solution, the mass of Na2SO4 needed is more than twice the mass of NaCl needed. D More moles of ions are present in a given volume of 0.10 M Na2SO4 than in the same volume of 0.10 M NaCl. E The degree of dissociation of Na2SO4 in solution is significantly greater than that of NaCl.

D

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

A

Equal numbers of moles of He(g), Ar(g), and Ne(g) are placed in a glass vessel at room temperature. If the vessel has a pinhole-sized leak, which of the following will be true regarding the relative values of the partial pressures of the gases remaining in the vessel after some of the gas mixture has effused? A PHe < PNe < PAr B PHe < PAr < PNe C PNe < PAr < PHe D PAr < PHe < PNe E PHe = PAr = PNe

A

Refer to the following compounds. (A) CH3CH2CH2CH3 (B) CH3CH2CH2OH (C) CH3COCH3 (D) CH3COOH (E) CH3CH2CH2NH2 Is the LEAST soluble in water A CH3CH2CH2CH3 B CH3CH2CH2OH C CH3COCH3 D CH3COOH E CH3CH2CH2NH2

A

The Maxwell-Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. Which gas has the greater molar mass? A Gas A B Gas B C Both gases have the same molar mass. D It cannot be determined unless the pressure of each sample is known.

A

The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10−19J. ColorWavelengthRed647−760nmOrange585−647nmYellow575−585nmGreen491−575nmBlue424−491nmViolet300−424nm Using the wavelength information provided above, what is the color of the light? A Red B Orange C Yellow D Blue

B

Which of the following pieces of laboratory glassware should be used to most accurately measure out a 25.00 mL sample of a solution? A 5 mL pipet B 25 mL pipet C 25 mL beaker D 25 mL Erlenmeyer flask E 50 mL graduated cylinder

B

How many moles of Na+ ions are in 100.mL of 0.100MNa3PO4(aq) ? A 0.300mol0.300mol B 0.100mol0.100mol C 0.0300mol0.0300mol D 0.0100mol0.0100mol

C

If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100. mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.) A 4 × 10−4 mol B 3 × 10−4 mol C 4 × 10−6 mol D 3 × 10−6 mol

C

Nonane and 2,3,4-trifluoropentane have almost identical molar masses, but nonane has a significantly higher boiling point. Which of the following statements best helps explain this observation? A The C-F bond is easier to break than the C-H bond. B The C-F bond is more polar than the C-H bond. C The carbon chains are longer in nonane than they are in 2,3,4-trifluoropentane. D The carbon chains are farther apart in a sample of nonane than they are in 2,3,4- trifluoropentane.

C

Of the following organic compounds, which is LEAST soluble in water at 298 K? A CH3OH, methanol B CH3CH2CH2OH, l-propanol C C6H14, hexane D C6H12O6, glucose E CH3COOH, ethanoic (acetic) acid

C

Solid carbon tetrachloride, CCl4(s), is represented by the diagram above. The attractions between the CCl4 molecules that hold the molecules together in the solid state are best identified as A polar covalent bonds B nonpolar covalent bonds C intermolecular attractions resulting from temporary dipoles D intermolecular attractions resulting from permanent dipoles

C

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? 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

A student prepared five solutions of CuSO4 with different concentrations, and then filled five cuvettes, each containing one of the solutions. The cuvettes were placed in a spectrophotometer set to the appropriate wavelength for maximum absorbance. The absorbance of each solution was measured and recorded. The student plotted absorbance versus concentration, as shown in the figure above. Which of the following is the most likely explanation for the variance of the data point for the 0.600 M CuSO4 solution? A The cuvette into which the 0.600 M solution was placed had some water droplets inside. B The cuvette into which the 0.600 M solution was placed was filled slightly more than the other cuvettes. C The wavelength setting was accidentally moved away from that of maximum absorbance. D The cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer.

D

A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. A wavelength of 510nm corresponds to an approximate frequency of 6×1014s−1. What is the approximate energy of one photon of this light? A 9×1047J9×1047J B 3×1017J3×1017J C 5×10−7J5×10−7J D 4×10−19J

D

A vessel contains Ar(g) at a high pressure. Which of the following statements best helps to explain why the measured pressure is significantly greater than the pressure calculated using the ideal gas law? A The molar mass of Ar is relatively large. B A significant number of Ar2 molecules form. C The attractive forces among Ar atoms cause them to collide with the walls of the container with less force. D The combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container.

D

Equal volumes of solutions in two different vessels are represented above. If the solution represented in vessel 1 is KCl(aq), then the solution represented in vessel 2 could be an aqueous solution of A KCl with the same molarity as the solution in vessel 1 B KCl with twice the molarity of the solution in vessel 1 C CaCl2 with the same molarity as the solution in vessel 1 D CaCl2 with twice the molarity of the solution in vessel 1

D

Which of the following best helps to explain why CCl4 is a liquid whereas CI4 is a solid when both are at 25°C? A The dipole moment of the CCl4 molecule is larger than that of the CI4 molecule because Cl is more electronegative than I. B The dipole moment of the CI4 molecule is larger than that of the CCl4 molecule because there is stronger repulsion between electrons in the C-I bonds compared to the repulsion between electrons in the C- Cl bonds. C The London dispersion forces are stronger in CCl4 than in CI4 because Cl is more electronegative than I. D The London dispersion forces are stronger in CI4 than in CCl4 because CI4 has a more polarizable electron cloud than CCl4

D

The student made the standard curve above. Which of the following most likely caused the error in the point the student plotted at 0.050MCo2+(aq) ? A There was distilled water in the cuvette when the student put the standard solution in it. B There were a few drops of the 0.100MCo2+(aq)0.100MCo2+(aq) standard solution in the cuvette when the student put the 0.050 M0.050 ⁢M standard solution in it. C The student used a cuvette with a longer path length than the cuvette used for the other standard solutions. D The student did not run a blank between the 0.050MCo2+(aq)0.050MCo2+(aq) solution and the one before it.

A

Which of the following behaves most like an ideal gas at the conditions indicated? A H2(g) molecules at 10-3 atm and 200oC B O2(g) molecules at 20 atm and 200oC C SO2(g) molecules at 20 atm and 200oC D NH3(g) molecules at 20 atm and 200oC E NH3(g) molecules at 20 atm and 300oC

A

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

B

The volume of water that must be added in order to dilute 40 mL of 9.0 M HCl to a concentration of 6.0 M is closest to A 10 mL B 20 mL C 30 mL D 40 mL E 60 mL

B

When 4.0 L of He(g), 6.0 L of N2(g), and 10. L of Ar(g), all at 0°C and 1.0 atm, are pumped into an evacuated 8.0 L rigid container, the final pressure in the container at 0°C is A 0.5 atm B 1.0 atm C 2.5 atm D 4.0 atm

B

Four different liquid compounds in flasks at 20°C are represented above. The table below identifies the compounds. Flask C shows the most particles in the vapor phase. Which of the following is not shown in the model but best helps to explain why flask C must contain pentane? A The random motion of the particles within the liquids B The relative speeds of the vapor particles in each flask C The strength of the intermolecular forces between the particles in the liquids D The structural formula of the molecules of the liquid and vapor in each flask

C

The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure P1, as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample? A The average kinetic energy increases. B The average kinetic energy decreases. C The average kinetic energy stays the same. D It cannot be determined how the kinetic energy is affected without knowing P1 and P2.

C

Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas? A 50 K and 0.10 atm B 50 K and 5.0 atm C 500 K and 0.10 atm D 500 K and 50 atm

C

A 360. mg sample of aspirin, C9H8O4, (molar mass 180. g), is dissolved in enough water to produce 200. mL of solution. What is the molarity of aspirin in a 50. mL sample of this solution? A 0.0800 M B 0.0400 M C 0.0200 M D 0.0100 M E 0.00250 M

D

The ideal gas law best describes the properties of which of the following gases at 0°C and 1 atm? A PH3 B HBr C SO2 D N2

D

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? 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

Which of the following substances has the greatest solubility in C5H12(l) at 1 atm? A SiO2(s) B NaCl(s) C H2O(l) D CCl4(l) E NH3(g)

D

A 0.5 mol sample of He(g) and a 0.5 mol sample of Ne(g) are placed separately in two 10.0 L rigid containers at 25°C. Each container has a pinhole opening. Which of the gases, He(g) or Ne(g), will escape faster through the pinhole and why? A He(g) will escape faster because the He(g) atoms are moving at a higher average speed than the Ne(g) atoms. B Ne(g) will escape faster because its initial pressure in the container is higher. C Ne(g) will escape faster because the Ne(g) atoms have a higher average kinetic energy than the He(g) atoms. D Both gases will escape at the same rate because the atoms of both gases have the same average kinetic energy.

A

A balloon filled with 0.25 mol of He(g) at 273 K and 1 atm is allowed to rise through the atmosphere. Which of the following explains what happens to the volume of the balloon as it rises from ground level to an altitude where the air temperature is 220 K and the air pressure is 0.1 atm? A The volume will increase because the decrease in air pressure will have a greater effect than the decrease in temperature. B The volume will remain unchanged because of the counteracting effects of the decrease in temperature and the decrease in air pressure. C The volume will decrease because the decrease in temperature will have a greater effect than the decrease in air pressure. D It cannot be determined whether the volume of the balloon will increase, decrease, or remain the same without knowing the initial volume of the balloon.

A

Ar(g) deviates more from ideal behavior at extremely high pressures than Ne(g) does. Which of the following is one reason for this difference? A The particle volume of ArAr is greater than that of NeNe. B ArAr atoms have more valence electrons than NeNe atoms have, so ArAr atoms have greater interparticle forces. C The intermolecular forces between NeNe atoms are greater than those between ArAr atoms. D ArAr atoms are more attracted to the walls of the container than NeNe atoms are.

A

At 298 K and 1 atm, Br2 is a liquid with a high vapor pressure, and Cl2 is a gas. Those observations provide evidence that under the given conditions, the A forces among Br2 molecules are stronger than those among Cl2 molecules B forces among Cl2 molecules are stronger than the Cl−Cl bond C Br−Br bond is stronger than the Cl−Cl bond D Cl−Cl bond is stronger than the Br−Br bond

A

Gases generated in a chemical reaction are sometimes collected by the displacement of water, as shown above. Which of the following gases can be quantitatively collected by this method? A H2 B CO2 C HCl D SO2 E NH3

A

Which of the following best helps explain why the pressure of a sample of CH4(g) (molar mass 16g/mol) is closer to the pressure predicted by the ideal gas law than a sample of NH3(g) (molar mass 17g/mol) ? A NH3NH3 molecules are polar while CH4CH4 molecules are not, and the greater attractions between NH3NH3 molecules cause the molecules to collide with the walls of the container with less force. B NH3NH3 molecules have a greater molar mass than CH4CH4 molecules, so the NH3NH3 molecules collide with the walls of the container with more force. C CH4CH4 molecules have more hydrogen atoms than NH3NH3 molecules, so CH4CH4 molecules have more hydrogen bonding and greater intermolecular forces. D CH4CH4 molecules are larger than NH3NH3 molecules, so the actual CH4CH4 molecules take up a significant portion of the volume of the gas.

A

On the basis of the solubility curves shown above, the greatest percentage of which compound can be recovered by cooling a saturated solution of that compound from 90°C to 30°C? A NaCl B KNO3 C K2CrO4 D K2SO4 E Ce2(SO4)3

B

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

B

The survival of aquatic organisms depends on the small amount of O2 that dissolves in H2O. The diagrams above represent possible models to explain this phenomenon. Which diagram provides the better particle representation for the solubility of O2 in H2O, and why? A Diagram 1, because O2O2 molecules can form hydrogen bonds with the H2OH2O molecules. B Diagram 1, because O2O2 and H2OH2O are polar molecules that can interact through dipole-dipole forces. C Diagram 2, because the polar H2OH2O molecules can induce temporary dipoles on the electron clouds of O2O2 molecules. D Diagram 2, because the nonpolar O2O2 molecules can induce temporary dipoles on the electron clouds of H2OH2O molecules.

C

Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C? A The dispersion forces in NH3 are weaker than the dispersion forces in PH3. B The dispersion forces in NH3 are stronger than the dipole-dipole forces in PH3. C NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3. D NH3 has hydrogen bonding that is weaker than the dipole-dipole forces in PH3.

C

he diagrams above show the ultraviolet absorption spectra for two compounds. Diagram 1 is the absorption spectrum of pure acetone, a solvent used when preparing solutions for an experiment. Diagram 2 is the absorption spectrum of the solute for which the absorbance needs to be measured to determine its concentration. When the student reads the absorbance of the solution at 280nm, the result is too high. Which of the following is most likely responsible for the error in the measured absorbance? A The student added too little solute to the acetone before measuring its absorbance. B The student rinsed the cuvette with the solution before filling the cuvette with the solution. C The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone. D The wavelength setting was accidentally changed from 280nm280nm to 300nm300nm before the student made the measurement.

C

A 2 L container will hold about 4 g of which of the following gases at 0°C and 1 atm? A SO2 B N2 C CO2 D C4H8 E NH3

C: CO2

The diagram above is a molecular model of a gaseous diatomic element that is just above its boiling point. Intermolecular forces between the gas molecules will cause them to condense into the liquid phase if the temperature is lowered. Which of the following best describes how the model is limited in its depiction of the phenomenon? A It does not show how hydrogen bonds are constantly forming, breaking, and reforming, which results in a net force of attraction between the molecules. B It does not show how the interactions between ions and the induced molecular dipoles result in a net force of attraction between the molecules. C It does not show how the interacting permanent dipoles of the molecules result in a net force of attraction between the molecules. D It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.

D

Based on concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water? A Z < Y < X B Y < Z < X C Y < X < Z D X < Z < Y E X < Y < Z

E

Equal masses of He and Ne are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 6 atm? A 1 atm B 2 atm C 3 atm D 4 atm E 5 atm

E

Based on the data in the tables above, which of the following statements provides the best prediction for the boiling point of NaCl? A NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF. B NaCl will have a boiling point between that of NaF and MgO because the covalent character of the bonds in NaCl is intermediate between that of MgO and NaF. C NaCl will have a higher boiling point than MgO because the ions are spaced farther apart in NaCl. D NaCl will have a higher boiling point than MgO because the energy required to transfer electrons from the anion to the cation is larger in NaCl than in MgO.

A

The ionic compounds NaCl and MgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why? A Diagram 1 represents NaClNaCl; it has a lower melting point than MgSMgS has because the coulombic attractions between the singly charged Na+Na+ ions and the Cl−Cl− ions in NaClNaCl are stronger than those between the ions in MgSMgS. B Diagram 1 represents NaClNaCl; it has a lower melting point than MgSMgS because the coulombic attractions between its singly charged Na+Na+ ions and the Cl−Cl− ions are weaker than those between the ions in MgSMgS. C Diagram 1 represents MgSMgS; it has a lower melting point than NaClNaCl because the coulombic attractions between its doubly charged Mg2+Mg2+ ions and the S2−S2− ions are stronger than those between the ions in NaClNaCl. D Diagram 1 represents MgSMgS; it has a lower melting point than NaClNaCl because the coulombic attractions between the doubly charged Mg2+Mg2+ ions and the S2−S2− ions are weaker than those between the ions in NaClNaCl.

B

Which of the following most likely describes the solid represented in the diagram above? A It is soft and is a poor thermal and electrical conductor. B It has a low melting point and is a poor thermal and electrical conductor as a solid. C It is a brittle, water-soluble electrolyte that is a poor thermal and electrical conductor as a solid. D It is malleable and is an excellent thermal and electrical conductor as a solid.

C

Based on the structures shown above, which of the following statements identifies the compound with the higher boiling point and provides the best explanation for the higher boiling point? A Compound 1, because it has stronger dipole-dipole forces than compound 2 B Compound 1, because it forms hydrogen bonds, whereas compound 2 does not C Compound 2, because it is less polarizable and has weaker London dispersion forces than compound 1 D Compound 2, because it forms hydrogen bonds, whereas compound 1 does not

D

The liquefied hydrogen halides have the normal boiling points given above. The relatively high boiling point of HF can be correctly explained by which of the following? A HF gas is more ideal. B HF is the strongest acid. C HF molecules have a smaller dipole moment. D HF is much less soluble in water. E HF molecules tend to form hydrogen bonds.

E

Infrared spectroscopy is a useful tool for scientists who want to investigate the structure of certain molecules. Which of the following best explains what can occur as the result of a molecule absorbing a photon of infrared radiation? A The energies of infrared photons are in the same range as the energies associated with changes between different electronic energy states in atoms and molecules. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the energies of electronic transitions within the molecules. B The energies of infrared photons are in the same range as the energies associated with different vibrational states of chemical bonds. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the types and strengths of different bonds in the molecules. C The energies of infrared photons are in the same range as the energies associated with different rotational states of molecules. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the energies of transition between different rotational energy states of the molecules. D The energies of infrared photons are in the same range as the total bond energies of bonds within molecules. Chemical bonds can be completely broken as they absorb infrared photons of characteristic wavelengths, thus revealing the energies of the bonds within the molecules.

B

Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO3(aq) into their beakers. The reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. To determine the number of moles of Cu in the sample of the mixture, the students measured the absorbance of known concentrations of Cu(NO3)2(aq) using a spectrophotometer. A cuvette filled with some of the solution produced from the sample of the mixture was also tested. The data recorded by one student are shown in the table above. On the basis of the data provided, which of the following is a possible error that the student made? A The Cu(NO3)2(aq) from the sample of the mixture was not diluted properly. B The spectrophotometer was calibrated with tap water instead of distilled water. C The student labeled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentration. D The spectrophotometer was originally set to an inappropriate wavelength, causing the absorbance to vary unpredictably.

C

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

C

The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10−19J. Which of the following is closest to the frequency of the light with photon energy of 3.3×10−19J? A 5.0×10−53s−15.0×10−53s−1 B 5.0×10−16s−15.0×10−16s−1 C 5.0×1014s−15.0×1014s−1 D 5.0×1052s−15.0×1052s−1

C