AP Chem U1-5.2

How many moles of Na+ ions are in 100.mL of 0.100MNa3PO4(aq) ?

0.0300mol

The original solution used to make the solutions for the standard curve was prepared by dissolving 2.60g2.60g of CoCl2CoCl2 (molar mass 130.g/mol130.g/mol) in enough water to make 100.mL100.mL of solution. What is the molar concentration of the solution?

0.200 M

How many grams of CaCl2 (molar mass =111g/mol) are needed to prepare 100.mL of 0.100MCl−(aq) ions?

0.555g

Which of the following is the ground-state electron configuration of the F− ion?

1s2 2s2 2p6

Which of the following ground-state electron configurations represents the atom that has the lowest first-ionization energy?

1s2 2s2 2p6 3s1

An equimolar mixture of N2(g)N2(g) and Ar(g)Ar(g) is kept inside a rigid container at a constant temperature of 300 KK. The initial partial pressure of ArAr in the mixture is 0.75atm0.75atm. An additional amount of ArAr was added to the container, enough to double the number of moles of ArAr gas in the mixture. Assuming ideal behavior, what is the final pressure of the gas mixture after the addition of the ArAr gas?

2.25atm, because doubling the number of moles of ArAr doubles its partial pressure.

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?

About 0.20atm , because H2 comprises 20% of the total number of moles of gas.

The structure of one form of boron nitride is represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

If Na reacts with chlorine to form NaCl, which of the following elements reacts with Na to form an ionic compound in a one-to-one ratio, and why?

Br , because it has the same number of valence electrons as Cl .

Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°?

C2H4O2

A student obtains a liquid sample of green food coloring that is known to contain a mixture of two solid pigments, one blue and one yellow, dissolved in an aqueous solution of ethanol. Which of the following laboratory setups is most appropriate for the student to use in order to separate and collect a substantial sample of each of the two pigments?

Column Chromatography

RbCl has a high boiling point. Which of the following compounds is also likely to have a high boiling point, and why?

CsCl , because its elements have very different electronegativities and it is an ionic compound.

The reaction between solid copper and aqueous silver nitrate produces solid silver and a blue solution, as represented by the balanced equation shown above. Based on the balanced equation, which of the following identifies the oxidation and reduction half-reactions?

Cu(s)→Cu2+(aq)+2e− and Ag+(aq)+e−→Ag(s)

The diagrams above represent solutes present in two different dilute aqueous solutions before they were mixed. Water molecules are not shown. When the solutions were combined, a precipitation reaction took place. Which of the diagrams below is the best particle representation of the mixture after the precipitation reaction occurred?

D. AgCl precipitate with dissociated Na and NO3

The diagram above shows the distribution of speeds for a sample of N2(g)N2(g) at 25°C25°C. Which of the following graphs shows the distribution of speeds for a sample of O2(g)O2(g) at 25°C25°C (dashed line) ?

Dashed line to the left and up

The diagram above shows a thin-layer chromatogram of a mixture of products from a chemical reaction. The separation was performed using 50% ethyl acetate in hexane as the solvent (mobile phase) and silica gel as the polar stationary phase. On the basis of the chromatogram and the information about solvents in the table above, which of the following would be the best way to decrease the distance that the products travel up the plate?

Decrease the percentage of ethyl acetate in the solvent.

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?

Diagram 1 represents NaCl ; it has a lower melting point than MgS because the coulombic attractions between its singly charged Na+ ions and the Cl− ions are weaker than those between the ions in MgS .

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?

F−(aq)+H+(aq)→HF(aq)

Which graph best represents the changes in concentration of O2(g), and why?

Graph 1, because the rate of O2 consumption is half the rate at which NO is consumed; two molecules of NO react for each molecule of O2 that reacts.

The complete photoelectron spectrum for an element is shown above. Which of the following observations would provide evidence that the spectrum is consistent with the atomic model of the element?

In its compounds, the element tends to form ions with a charge of +1 .

When ClCl and FF form bonds with other atoms, the ClCl bonding electrons are more shielded from the positive ClCl nucleus than the FF bonding electrons are shielded from the positive FF nucleus.

It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.

Which of the following elements has the mass spectrum represented above?

Mo

Which statement best helps to explain the observation that NH3(l)NH3(l) boils at −28°C−28°C, whereas PH3(l)PH3(l) boils at −126°C−126°C?

NH3NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3PH3.

A 2mol2mol sample of F2(g)F2(g) reacts with excess NaOH(aq)NaOH(aq) according to the equation above. If the reaction is repeated with excess NaOH(aq)NaOH(aq) but with 1 mol1 mol of F2(g)F2(g), which of the following is correct?

The amount of OF2(g) produced is halved.

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?

The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.

Which of the following scientific claims about the bond in the molecular compound HFHF is most likely to be true?

The bond is highly polar.

The elements CC and SeSe have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from CC and SeSe is most likely to be true?

The carbon-to-selenium bond is nonpolar covalent.

The graph above shows the distribution of molecular speeds for four different gases at the same temperature. What property of the different gases can be correctly ranked using information from the graph, and why?

The molecular masses of the gases, because the gas molecules have the same average kinetic energy and mass can be calculated using the equation KEavg=(1/2)mv2.

The 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 280nm280nm, the result is too high. Which of the following is most likely responsible for the error in the measured absorbance?

The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone.

A student had two dilute, colorless solutions, HCl(aq)HCl(aq) and NaOH(aq)NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?

The temperature of the reaction mixture increases.

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?

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.

All the chlorides of the alkaline earth metals have similar empirical formulas, as shown in the table above. Which of the following best helps to explain this observation?

The two valence electrons of alkaline earth metal atoms are relatively easy to remove.

Which of the following best helps to explain why the electron affinity of Br has a greater magnitude than that of I?

There is a greater attraction between an added electron and the nucleus in Br than in I.

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)0.050MCo2+(aq) ?

There was distilled water in the cuvette when the student put the standard solution in it.

How many grams of CaCl2 (molar mass =111g/mol) are needed to prepare 100.mL of 0.100MCl−(aq) ions?

2.22g

The electron cloud of HFHF is smaller than that of F2F2 , however, HFHF has a much higher boiling point than F2F2 has. Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HFHF?

Liquid F2F2 has weak dispersion force attractions between its molecules, whereas liquid HFHF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 26 amu represents an isotope of which of the following elements?

Mg with 14 neutrons

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?

Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states.

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

Molar mass of the compound, mass of the sample

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) ?

NH3 molecules are polar while CH4 molecules are not, and the greater attractions between NH3 molecules cause the molecules to collide with the walls of the container with less force.

When 0.20 M NH4Cl(aq) and 0.20 M NaOH(aq) are mixed, the reaction represented by the equation above occurs and a strong smell of ammonia, NH3, is observed. Based on this information, which of the following statements is true?

NH4+(aq) is a stronger acid than H2O(l) is.

Using the wavelength information provided above, what is the color of the light?

Orange

The complete photoelectron spectrum of an element is given above. Which of the following electron configurations is consistent with the spectrum?

1s2 2s2 2p6 3s2 3p3

Which of the following best represents the ground-state electron configuration for an atom of selenium?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4

The half-reactions for the oxidation-reduction reaction between Al(s)Al(s) and Zn2+(aq)Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s)Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients?

2

The particle diagram above represents an aqueous solution of a weak monoprotic acid. The white circles represent HH atoms. Which of the following shows the species that act as a Brønsted-Lowry base and its conjugate acid, in that order, in the solution?

2 H atoms and 3 H atoms

Which of the following numerical expressions gives the number of particles in 2.0g of Ne?

2.0g / 20.18g/mo * (6.0×10^23 particles/mol)

Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag+(aq)Ag+(aq) and Ni(s)Ni(s) based on the half-reactions represented above?

2Ag+(aq)+Ni(s)→2Ag(s)+Ni2+(aq)

A sample of carbonate rock is a mixture of CaCO3 and MgCO3. The rock is analyzed in a laboratory, and the results are recorded in the table above. Which columns in the table provide all the information necessary to determine the mole ratio of Ca to Mg in the rock?

3, 4, 6, 7

A wavelength of 510nm510nm corresponds to an approximate frequency of 6×1014s−16×1014s−1. What is the approximate energy of one photon of this light?

4×10^−19J

Which of the following is closest to the frequency of the light with photon energy of 3.3×10−19J?

5.0×1014s−1

Which of the following Lewis diagrams best represents the bonding in the N2O molecule, considering formal charges?

:N:::N:O

A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?

A cube of metal was changed into a flat sheet of metal.

A student mixes 20.0g20.0g of white KClKCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?

After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.

Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms?

B. Substitutional metal

When the chemical reaction 2NO(g)+O2(g)→2NO2(g) is carried out under certain conditions, the rate of disappearance of NO(g) is 5.0×10−5 Ms−1. What is the rate of disappearance of O2(g) under the same conditions?

Because two molecules of NO are consumed per molecule of O2 , the rate of disappearance of O2(g) is 2.5×10−5 Ms−1 .

The initial rate of formation of CO2(g) from the chemical reaction represented by the equation above was studied in two separate experiments. The table above provides the experimental conditions used. If both experiments are carried out with finely powdered samples of the solid and 50.0mL of HCl(aq), which experiment, if any, will have the faster initial rate of formation of CO2(g) and why?

CO2(g) will be formed at a faster rate in experiment 2 because more H+ particles can react per unit time.

A student performed a fractional distillation of a mixture of two straight-chain hydrocarbons, C7H16C7H16 and C8H18C8H18. Using four clean, dry flasks, the student collected the distillate over the volume ranges (AA, BB, CC, and DD) shown in the graph above. Over what volume range should the student collect the distillate of the compound with the stronger intermolecular forces?

D (second flat area)

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?

Diagram 2, because the polar H2O molecules can induce temporary dipoles on the electron clouds of O2 molecules.

For the dissolution of HClHCl in water represented above, which of the following pairs includes the Brønsted-Lowry bases?

H2O(l) and Cl−(aq)

The figure presents two test tubes. The first test tube is labeled I 2 solid in H 2 O liquid. It is filled slightly more than halfway with a colorless solution. A black circle labeled I 2 solid is in the bottom of the test tube. The second test tube is labeled I 2 solid in C 6 H 14 liquid. It is filled slightly more than halfway with a purple solution. A student places a piece of I2(s) in 50.0 mL of H2O(l), another piece of I2(s) of the same mass in 50.0 mL of C6H14(l), and shakes the mixtures. The results are shown above. What do the results indicate about the intermolecular interactions of the substances?

I2 and C6H14 have similar intermolecular interactions, and I2 and H2O do not.

The diagram above shows two resonance structures for a molecule of C6H6. The phenomenon shown in the diagram best supports which of the following claims about the bonding in C6H6 ?

In the C6H6 molecule, all the bonds between the carbon atoms have the same length.

Steel is an alloy containing Fe atoms and C atoms. Which of the following diagrams best represents the particle-level structure of steel?

Interstitial, with the Carbon as the smaller ion

Two pure elements react to form a compound. One element is an alkali metal, XX, and the other element is a halogen, ZZ. Which of the following is the most valid scientific claim that can be made about the compound?

It contains ionic bonds.

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

It does not conduct electricity because its ions cannot move freely within the solid.

A student has a 1g sample of each of the following compounds: NaCl, KBr, and KCl. Which of the following lists the samples in order of increasing number of moles in the sample?

KBr<KCl<NaCl

When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because H2(g) is oxidized.

The compound C6H8O6C6H8O6 reacts with I2I2 according to the reaction represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because I2I2 is reduced.

Equal volumes of 0.2M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

Pb2+(aq)+2Br−(aq)→PbBr2(s)

The initial rates of the reaction represented by the equation shown above were measured for different initial concentrations of NO(g) and Cl2(g). Based on the data given in the table above, which of the following is the rate law expression for the reaction, and why?

Rate=k[NO]2[Cl2] , because the initial rate quadrupled when [NO] was doubled and doubled when [Cl2] was doubled.

The particle-level diagram above represents the structure of solid KFKF. Although the molar mass of KClKCl is greater than that of KFKF, the density of KClKCl is actually less than that of KFKF. Which of the following representations of the structure of KClKCl best helps to explain this phenomenon?

Small + ions with larger - ions in a checkered pattern

The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?

Sr2+(aq)+SO42−(aq)→SrSO4(s)

Which of the following statements, if true, would support the claim that the NO3− ion, represented above, has three resonance structures?

The NO3− ion is not a polar species.

The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaF and MgF2 is shown in the table above. On the basis of Coulomb's law, which of the following best helps to explain the large difference between the lattice energies of NaF and MgF2 ?

The charge of the Mg cation is larger than that of the Na cation

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 ?

The concentration of the solution was actually lower than 0.150M .

The photoelectron spectrum for the element nitrogen is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom?

The electrons in the 2p sublevel have the smallest binding energy.

The diagrams above represent two samples of Xe gas in containers of equal volume at 280K. Which of the following correctly compares the two samples in terms of their deviation from ideal gas behavior and explains why?

The gas in sample 2 would deviate more from ideal behavior because the Xe atoms are closer together, leading to an increase in intermolecular attractions.

The reaction between C6H12O6 and O2 is represented by the balanced equation above. In an experiment, 0.30mol of CO2 was produced from the reaction of 0.05mol of C6H12O6 with excess O2. The reaction was repeated at the same temperature and in the same container, but this time 0.60mol of CO2 was produced. Which of the following must be true?

The initial amount of C6H12O6 in the container must have been 0.10mol .

A student is given two 10g samples, each a mixture of only NaCl(s) and KCl(s) but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of KCl(s) ?

The mass of Cl in each mixture

A 5.0g sample of MgCl2 may contain measurable amounts of other compounds as impurities. Which of the following quantities is (are) needed to determine that the sample is pure MgCl2 ?

The mass of Mg and the mass of Cl in the sample

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?

The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.

Diagram 1 above shows equimolar samples of two gases inside a container fitted with a removable barrier placed so that each gas occupies the same volume. The barrier is carefully removed as the temperature is held constant. Diagram 2 above shows the gases soon after the barrier is removed. Which statement describes the changes to the initial pressure of each gas and the final partial pressure of each gas in the mixture and also indicates the final total pressure?

The partial pressure of each gas in the mixture is half its initial pressure; the final total pressure is half the sum of the initial pressures of the two gases.

Ar(g)Ar(g) deviates more from ideal behavior at extremely high pressures than Ne(g)Ne(g) does. Which of the following is one reason for this difference?

The particle volume of ArAr is greater than that of NeNe.

In aqueous solution, the reaction represented by the balanced equation shown above has the experimentally determined rate law: rate=k[S2O82−][I−]. If the concentration of [S2O82−] is doubled while keeping [I−] constant, which of the following experimental results is predicted based on the rate law, and why?

The rate of reaction will double, because the rate is directly proportional to [S2O82−] .

A student was asked to formulate a hypothesis about what would happen if 100.mL of 0.1MNaOH(aq) at 25°C was combined with 100.mL of 0.1MMgCl2(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?

The resulting solution would contain a precipitate.

Four different liquid compounds in flasks at 20°C20°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?

The strength of the intermolecular forces between the particles in the liquids

Lewis diagrams of molecules of three different hydrocarbons are shown above. Which of the following claims about the molecules is best supported by the diagrams?

The strongest carbon-to-carbon bond occurs in molecule 3.

The mass spectrum of the element Sb is most likely represented by which of the following?

Two peaks at 121 and 123, with 121>123.

A 100mL100mL sample of 0.1MMgCl2(aq)0.1MMgCl2(aq) and a 100mL100mL sample of 0.2MNaOH(aq)0.2MNaOH(aq) were combined, and Mg(OH)2(s)Mg(OH)2(s) precipitated, as shown by the equation above. If the experiment is repeated using solutions of the same molarity, which of the following changes in volume will double the amount of Mg(OH)2(s)Mg(OH)2(s) produced?

Using twice the volume of MgCl2(aq)MgCl2(aq) and twice the volume of NaOH(aq)

Two different ionic compounds each contain only copper and chlorine. Both compounds are powders, one white and one brown. An elemental analysis is performed on each powder. Which of the following questions about the compounds is most likely to be answered by the results of the analysis?

What is the formula unit of each compound?

Which of the following best helps explain why the electronegativity of ClCl is less than that of FF?

When ClCl and FF form bonds with other atoms, the ClCl bonding electrons are more shielded from the positive ClCl nucleus than the FF bonding electrons are shielded from the positive FF nucleus.

A student has samples of two pure compounds, XClO3 and ZClO3, which contain unknown alkali metals X and Z. The student measures the mass of each sample and then strongly heats the samples to drive off all the oxygen, leaving solid residues of XCl and ZCl. The student measures the mass of the solid residue from each sample. Which of the following questions can be answered from the results of the experiment?

Which has the greater molar mass, X or Z ?

A student has two samples of NaCl, each one from a different source. Assume that the only potential contaminant in each sample is KCl. The student runs an experiment to determine the percent by mass of chlorine in each sample. From the results of this experiment alone, which of the following questions is most likely to be answered?

Which sample has the higher purity?

In the following diagrams, elements are represented by X and Z, which form molecular compounds with one another. Which diagram represents a molecule that has a bent molecular geometry?

Z - X - Z with full octet on X

A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are

equally shared and form nondirectional bonds

Based on their Lewis diagrams, which of the following pairs of liquids are most soluble in each other?

Like dissolves like: two polar compounds = H5C2OH and H2O

The table above summarizes data given to a student to evaluate the type of change that took place when substance X was mixed with water. The student claimed that the data did not provide enough evidence to determine whether a chemical or physical change took place and that additional tests were needed. Which of the following identifies the best way to gather evidence to support the type of change that occurred when water and X were mixed?

Measuring the electrical conductivities of X and the mixture of water and X

An experiment was conducted to determine the rate law for the reaction A2(g)+B(g)→A2B(g). The table above shows the data collected. Based on the data in the table, which statement is correct?

Since the rate law can be expressed as rate=k[A2][B] , doubling the concentrations of A2 and B will quadruple the rate of the reaction.

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?

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.

Which of the following represents an electron configuration that corresponds to the valence electrons of an element for which there is an especially large jump between the second and third ionization energies? (Note: n represents a principal quantum number equal to or greater than 2.)

ns2