Exam 2nd Period

The mass spectrum represented above is most consistent with which of the following elements?

b. Gd

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?

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?

b. Mass percent of Na

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?

b. The spectrum shows a single electron in the 2p2p subshell.

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

big white dots, small gray dots

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?

c- two O's have 4 valence, hydrogen bond bt h and o

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?

c. 186.3amu

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

c. 1s- 2, 2s-2, 2p-2 in this first, 1 in the second, 1 in the third. 8 total

Which of the following is the correct electron configuration for a ground-state atom of magnesium (atomic number 12) ?

c. 1s22s22p63s2

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?

+-+-+-- ionic

What charge does Al typically have in ionic compounds, and why?

+3, because it has three valence electrons.

How many unpaired electrons are in the atom represented by the electron configuration above?

0

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?

2.3atm, because the pressure PP increases by the proportion 313283313283.

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) ?

2Al(s)+3Sn2+(aq)→2Al3+(aq)+3Sn(s)

Which of the Lewis diagrams shown above is the more likely structure of CO2, and why?

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

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

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

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) ?

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

In the reaction between C5H5N(aq) and HCl(aq) represented above, C5H5N acts as

a Brønsted-Lowry base

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

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

A 500.mL aqueous solution of Na3PO4 (molarmass=164g/mol) was prepared using 82gof the solute. What is the molarity of Na3PO4 in the resulting solution?

1.0M

How many grams of NaCl (molarmass=58g/mol) are needed to prepare 100.mL of a 0.25M NaCl solution?

1.5g

Based on the Lewis diagram for NH3, shown above, the H-N-H bond angle is closest to which of the following?

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?

4×10^−19J

Which of the following numerical expressions gives the number of moles in 5.0g of CaO?

5.0/56

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?

5.6×10^14s−1

Which of the following represents the oxidation half-reaction based on the balanced ionic equation shown above?

5Fe2+(aq)+MnO4−(aq)+8H+(aq)→5Fe3+(aq)+Mn2+(aq)+4H2O(l)

In an experiment on the photoelectric effect, a photon with a frequency of 7×1014s−1 was absorbed by a sample. What is the approximate energy of this photon?

5×10−19J

What volume of a 0.100MHCl stock solution should be used to prepare 250.00mL of 0.0250MHCl?

62.5mL

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?

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

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?

Ag+(aq)+Cl−(aq)→AgCl(s)

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

All single bonds, o has 4 unpaired electrons, n has 2 unpaired

The particulate-level diagram shown above best helps to explain which of the following properties of ionic solids?

Brittleness

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?

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 structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite?

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

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

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.

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?

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

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?

CsCs, because it is in the same group as Rb

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?

Cu2+(aq)+2e−→Cu(s)

Which of the diagrams above best represents the CH2O molecule, and why?

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

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

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

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?

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

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?

Distillation

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) ?

Dotted line has less slope and is more spanned out (draw a pic. you know this)

The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct?

Gas Z has a smaller molar mass than gas X.

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?

H2O(g)

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

HCCl

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

HF(aq)+OH−(aq)→H2O(l)+F−(aq)

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?

HS−

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?

In the RbRb atom the valence electron is farther from its nucleus than the valence electron of LiLi is from its nucleus.

Which of the following indicates whether the solid substance represented by the particulate diagram shown above conducts electricity and explains why or why not?

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

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?

It conducts electricity because ions are free to move.

Which of the following best describes the process represented above that takes place when NH3 is added to water?

It is an acid-base reaction in which a proton is exchanged from H2OH2O to NH3NH3.

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?

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

2Mg(s)+SiCl4(l)→2MgCl2(s)+Si(s) Which of the following statements about the reaction represented above is correct?

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

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

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?

Mg2+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?

NH3(aq)+H+(aq)→NH4+(aq)

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?

One piece of solid substance was changed into small pieces.

Which of the following methods is most appropriate to use to determine the number of different-colored components in a sample of black ink?

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

The complete photoelectron spectrum of an element is given above. Which labeled peak corresponds to the 1s electrons and why?

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

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?

SO2, because it has the largest molecular volume.

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?

Solvent C

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?

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

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?

The atoms in the CO2CO2 molecules increase their vibration as the bonds between the atoms bend and stretch.

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

The bonding in the compound is nonpolar covalent.

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?

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

Which of the following claims about a binary compound in which the bonding is ionic is most likely to be scientifically valid?

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

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?

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

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?

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

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 1.0atm and 25°C.

The molar mass of Cu

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?

The molar mass of each gas

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?

The molar masses of XX and Z

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?

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

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?

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

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?

The precipitate has a high melting point.

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?

The resulting mixture was cloudy.

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?

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

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.)

Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL200.0mL of 0.200MHNO3(aq), because these are the required stoichiometric amounts

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?

What is the empirical formula of the compound?

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?

What is the molar mass of MM?

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

c. The valence electron of KK experiences a lower effective nuclear charge than the valence electrons of CaCa.

A 1.0mol sample of which of the following compounds has the greatest mass?

d. N2O5

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

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

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 chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaINaI formed.

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?

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

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

b. 91 amu

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?

Allotrope IIII, because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P4P4 molecules in allotrope II.

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?

Bubbles formed when the two solutions were combined.

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 the following best helps explain this deviation?

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

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?

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

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?

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.

C6H5COOH(aq)+NaOH(aq)→C6H5COONa(aq)+H2O(l) Which of the following identifies a conjugate acid-base pair in the reaction represented above?

acid- C6H5COOH, conjugate base- C6H5COO-

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?

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