AP Chem Midterm Review

What is the change in enthalpy for the reaction A-->B

+50 kJ, endothermic

When 1 mole of methane (CH₄) is burned at constant pressure, -890 kJ/mol of energy is released as heat. If a 3.17 g sample of methane is burned at constant pressure, what will be the value of ΔH?

-176 kJ

According to the equation above, how many moles of potassium chlorate, KClO3 , must be decomposed to generate 1.0 L of O2 gas at standard temperature and pressure?

2/3(1/22.4)mol

The Lewis structure for BI3 has (24, 27, 30) total electrons and (6,8) shared electrons.

24 ; 6

Based on periodic trends and the data in the table above, which of the following are the most probable values of the atomic radius and the first ionization energy for potassium, respectively?

242 pm, 419 kJ/mol

Draw the Lewis structure of xenon difluoride (XeF2) and give the number of lone pairs of electrons around the central atom.

3

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?

3 atm

H2SeO4(aq) + 2Cl-(aq) + 2H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l) S8(s) + 8O2(g) → 8SO2(g) 3Br2(aq) + 6OH-(aq) → 5Br-(aq) + BrO3-(aq) + 3H2O(l) Ca2+(aq) + SO42-(aq) → CaSO4(s) PtCl4(s) + 2Cl-(aq) → PtCl62-(aq) A reaction in which the same reactant undergoes both oxidation and reduction

3Br2(aq) + 6OH-(aq) → 5Br-(aq) + BrO3-(aq) + 3H2O(l)

Equimolar samples of CH3OH(l) and C2H5OH(l) are placed in separate, previously evacuated, rigid 2.0 L vessels. Each vessel is attached to a pressure gauge, and the temperatures are kept at 300 K. In both vessels, liquid is observed to remain present at the bottom of the container at all times. The change in pressure inside the vessel containing CH3OH(l) is shown below.

A physical change takes place because intermolecular attractions are overcome.

In the table above, which of the following diagrams best represents the change in energy as the reaction represented below proceeds?

A. Look at Doc

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

A. Look at document

M+ is an unknown metal cation with a +1 charge. A student dissolves the chloride of the unknown metal, MCl, in enough water to make 100.0 mL of solution. The student then mixes the solution with excess AgNO3 solution, causing AgCl to precipitate. The student collects the precipitate by filtration, dries it, and records the data shown below. (The molar mass of AgCl is 143 g/mol.) Which of the following diagrams best represents the AgNO3 solution before the reaction occurs?

A. Look at the document for this answer.

Atoms of Mg combine with atoms of F to form a compound. Atoms of which of the following elements combine with atoms of F in the same ratio?

Ba

Which of the following particulate diagrams best shows the formation of water vapor from hydrogen gas and oxygen gas in a rigid container at 125 ℃?

C. Look at document

A student has a 1g sample of each of the following compounds: MgCl2, CaBr2, and CaCl2. Which of the following lists the samples in order of increasing number of moles in the sample?

CaBr2 < CaCl2 < MgCl2

Which of the following lists Mg, P, and Cl in order of increasing atomic radius?

Cl < P < Mg

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 elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. One of the following statements is true. Which true statement would be the best basis for concluding that the sample was pure Te?

I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope

If a central atom has a total of two groups and/or lone pairs attached to it, the electron domain (group) geometry about the central atom is

Linear

OCS has what molecular geometry?

Linear

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 25 amu represents an isotope of which of the following elements?

Mg with 13 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 sample of a compound contains 6.42g of Sulfur and 22.8g fluorine. Which of the following represents the empirical formula of the compound?

SF6

Which of the following gasses deviates most from ideal behavior?

SO2

The masses of carbon and hydrogen in samples of four pure hydrocarbons are given above. The hydrocarbon in which sample has the same empirical formula as propene, C3H6 ?

Sample B: Mass of C 72g Mass of H 12g

You have two samples of water. Sample X has a volume of 750 mL and a temperature of 42 ° C. Sample Y has a volume of 380 mL and a temperature of 42 ° C. Which sample contains the most heat?

Sample X

Predict the bond angle at the central atom of ozone (O3)

Slightly less than 120°

Which of the following angles is the best choice to describe the bond angle in nitrite (NO2-)?

Slightly less than 120°

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?

The cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer.

For element X represented above, which of the following is the most likely explanation for the large difference between the second and third ionization energies?

The electron removed during the third ionization is, on average, much closer to the nucleus than the first two electrons removed were.

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.

You add 20 J of energy to a sample of water at 0 °C and detect no change in temperature. What best explains this observation?

The energy is used to break intermolecular bonds between water molecules.

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.

To metals of equal mass but with differing specific heat capacities are subjected to the same amount of heat. Which metal will undergo the largest change in temperature if neither metal changes phase?

The metal with the higher heat capacity

Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l) 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. In one student's experiment the reaction proceeded at a much slower rate than it did in the other students' experiments. Which of the following could explain the slower reaction rate?

The student used a 1.5 M solution of HNO3(aq) instead of a 15.8 M solution of HNO3(aq).

Of the following, the best explanation for the fact that most gasses are easily compressed is that the molecules in a gas

are relatively far apart

To catalyze a biochemical reaction, an enzyme typically

binds temporarily to reactant molecules to lower the activation energy of the reaction binds

In the diagram below, which of the labeled arrows identifies hydrogen bonding in water?

d

A sample of unknown gas from a cylinder is collected over water in the apparatus shown above. After all the gas sample has been collected, the water levels inside and outside the gas collection tube are made the same. Measurements that must be made to calculate the molar mass of the gas include all the following EXCEPT

initial and final mass of the gas cylinder

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

After a certain pesticide compound is applied to crops, its decomposition is a first-order reaction with a half-life of 56 days. What is the rate constant, k, for the decomposition reaction?

0.012 day-1

A solution is prepared by adding 32 g of CH3OH (molar mass 32 g) to 180. g of H2O (molar mass 18 g). The mole fraction of CH3OH in this solution is closest to which of the following?

0.1

In 2.00 mol of copper(II) sulfate pentahydrate (CuSO4.5H2O), there are

1.08 x 10^25 oxygen atoms

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

1s^2 2s^2 2p^6 3s^1

When the equation for the reaction represented above is balanced and all coefficients are reduced to the lowest whole-number terms, the coefficient for O2(g) is

5

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 x 10-19 J. Which of the following is closest to the frequency of the light with photon energy of 3.3 x 10-19 J?

5.0 x 10^14 s-1

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu, a student dissolves a small preweighed sample in HNO3(aq). Ag+(aq)and Cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process?

Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

A student mixes 20.0g of white KCl 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 20.0 g.

The mass spectrum of element X is presented in the diagram above. Based on the spectrum, which of the following can be concluded about element X?

Atomic mass of X is between 91 and 92

The first five ionization energies of a second-period element are listed in the table above. Which of the following correctly identifies the element and best explains the data in the table?

B, because it has three valence electrons

Which of the following is the best description of ionic bonding?

Bonding that occurs between elements with very different electronegativites, and with transfer of electrons.

A particle view of a sample of H2O2(aq) is shown above. The H2O2(aq) is titrated with KMnO4(aq), as represented by the equation below. 2MnO4-(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 5O2(g) + 8H2O(l) Which of the following particle views best represents the mixture when the titration is halfway to the equivalence point? (H2O molecules and H+ ions are not shown.)

C. Look at document

Addition of sulfurous acid (a weak acid) to barium hydroxide (a strong base) results in the formation of a precipitate. The net ionic equation for this reaction is:

C3H8(g) + O2(g) → H2O(g) + CO2(g)

Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the molecular formula of the compound?

C4H8

NO(g) + NO3(g) → 2 NO2(g) The reaction between NO(g) and NO3(g) is represented by the equation above. Which of the following orientations of collision between NO(g) and NO3(g) is most likely to be effective?

D. Look at doc for answer

The best Lewis structures of SO2 and O3 include expanded valence structures such as O = S = O and O = O = O.

False

HCl(q) + H2O(l) → H3O+(aq) + Cl-(aq) For the dissolution of HCl in water represented above, which of the following pairs includes the Brønsted-Lowry bases?

H2O(l) and Cl-(aq)

Which do you predict to have the strongest CN bond?

HCN

Which of the following compounds contains the WEAKEST bonds to hydrogen?

HF

Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented above?

Hydrogen Bond

Consider a potential energy diagram for the interaction of a sodium ion (Na+) with a chloride ion (Cl-). Which of the following statements is/are true? I) Repulsive forces predominate at very small internuclear distances. II) The minimum potential energy occurs when attractive forces are greatest. III) Attractive forces are linearly dependent on the internuclear distance.

I only

Which of the following compounds have a central atom with an expanded octet? I) SCl6 II) BF3 III) Br3- IV) CH3Cl

I, III

Which of the following compounds has only single bonds? I) SF6 II) BN III) F2 IV) SiH4

I, III, IV

Which of the following represents a pair of isotopes?

I. 6 | 14 and II. 6 | 13

A catalyst:

Increases the rate of a chemical reaction but is not consumed in the process.

If the electronegativity difference between atoms is close to zero, which of the following would NOT be a reasonable expectation?

Ionic bonding

What is NOT an alloy?

Iron

The effective nuclear charge experienced by the outermost electron of K is different than the effective nuclear charge experienced by the outermost electron of Ar. This difference best accounts for which of the following?

K has a lower first ionization energy than Ar

Among the following molecules, which has the strongest bonds?

N2

Which of the following contains only one unshared pair of valence electrons:

NH3

Which of the following is the conjugate acid of NH2- ?

NH3

O3 (g) + O(g) → 2 O2(g) The decomposition of O3(g) in the upper atmosphere is represented by the equation above. The potential energy in the upper atmosphere is diagram for the decomposition of O3(g) in the presence and absence of NO(g) is given below. Which of the following mechanisms for the catalyzed reaction is consistent with the equation and diagram above?

O3(g) + NO(g) → NO2(g) + O2(g) slow NO2(g) + O(g) → NO(g) + O2(g) fast

Predict the electron domain geometry of IF5.

Octahedral

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 gasses remaining in the vessel after some of the gas mixture has effused?

PHe < PNe < PAr

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

The diagram below shows the reaction between hydrogen and iodine. This reaction to form iodide

Releases heat energy.

When a buret is rinsed before a titration, which of the techniques below is the best procedure?

Rinse the buret two times: each time with some of the titrant solution.

A 0.35 g sample of Li(s) is placed in an Erlenmeyer flask containing 100 mL of water at 25°C. A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated. After all of the Li(s) has reacted with H2O(l), the solution in the flask is added to a clean, dry buret and used to titrate an aqueous solution of a monoprotic acid. The pH curve for this titration is shown in the diagram below What will be the effect on the amount of gas produced if the experiment is repeated using 0.35 g of K(s) instead of 0.35 g of Li(s) ?

Some gas will be produced but less than the amount of gas produced with Li(s).

The mass percent of oxygen in pure glucose, C6H12O6, is 53.3 percent. A chemist analyzes an impure sample of glucose and determines that the mass percent of oxygen is 48.2 percent. Which of the following impurities could account for the low mass percent of oxygen in the sample? ****

Sucrose, C12H22O11

Which of the following correctly compares the atomic radius of F to that of O and provides the best explanation?

The atomic radius of F is smaller than that of O because F has a greater effective nuclear charge than O does.

Two flexible containers for gasses are at the same temperature and pressure. One holds 0.50 grams of hydrogen and the other holds 8.0 grams of oxygen. Which of the following statements regarding these gas samples is FALSE?

The average speed of the hydrogen molecules is the same as the average speed of the oxygen molecules.

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

The molecular masses of the gasses, because the gas molecules have the same average kinetic energy and mass can be calculated using the equation KE = 1/2mv^2.

XY2 → X + Y2 The equation above represents the decomposition of a compound XY2. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY2. Which of the following most likely accounts for the difference between reaction path one and reaction path two?

The presence of a catalyst in path two

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 0.1M MgCl2 (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.

The diagrams below 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 280 nm, 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.

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

A bent molecular geometry can occur from which of the following electron group geometries?

Trigonal planar and tetrahedral

An experiment is performed to measure the mass percent of CaCo3(s) in eggshells. Five different samples of CaCO3(s) of known mass react with an excess of 2.0 M HCl(aq) in identical sealed, rigid reaction vessels. The pressure of the gas produced is measured with a pressure gauge attached to the reaction vessel. Since the reaction is exothermic, the reaction system is cooled to its original temperature before the pressure is recorded. The experimental data are used to create the calibration line below. The experiment is repeated with an eggshell sample, and the experimental data are recorded in the table below. Which of the following modifications will increase the rate of the reaction the most?

Using eggshells that are more finely powdered than those used in the original experiment

Which of the following is the best piece of laboratory glassware for preparing 500.0 mL of an aqueous solution of a solid?

Volumetric flask

A student has two samples of NaCl, each one from a different source. Assume that the only potential contaminant in each sample is LiCl. 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 density?

A block of aluminum at 25 °C and 1 atm is heated until it is a liquid at 700 °C. It is then cooled back down until it is back in the initial state of being a solid at 25 °C and 1 atm. For this entire process (heating and cooling) ΔH is...

Zero

When 100 mL of 1.0 M Na3PO4 is mixed with 100 mL of 1.0 M AgNO3, a yellow precipitate forms and [Ag+] becomes negligibly small. Which of the following is a correct listing of the ions remaining in solution in order of increasing concentration?

[PO4^3-] < [NO3-] < [Na+]

A 50 gram sample of delicious pork rinds is placed in an open, constant pressure calorimeter that contains 3000 grams of water. The temperature of the water increases by 47 °C when the pork rinds are combusted. The heat capacity of the water is 4.184 J/g°C. Assume the heat lost to the calorimeter itself or to the air is negligible. Which of the following is correct for the SYSTEM? ****

ΔH = -590 kJ

3Ag(s) + 4HNO3 → 3AgNO3 + NO(g) + 2H2O The reaction of silver metal and dilute nitric acid proceeds according to the equation above. If 0.10 mole of powdered silver is added to 10. mL of 6.0 M nitric acid, the number of moles of NO gas that can be formed is

0.015 mole

How many lone pairs of electrons are on the central atom of SF5- ?

1

What are all of the angles in a trigonal bipyramidal geometry?

90° and 120°

Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s) 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?

B. Oxidation: Cu(s) --> Cu2+(aq)+2e- Reduction: Ag+(aq)+e- --> Ag(s)

A mixture of CO(g) and O2(g) is placed in a container, as shown above. A reaction occurs, forming CO2(g). Which of the following best represents the contents of the box after the reaction has proceeded as completely as possible?

B. The picture is the answer

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

N2O(g) + CO(g) → N2(g) + CO2(g) The rate of the reaction represented above increases significantly in the presence of Pd(s). Which of the following best explains this observation?

One of the reactants binds on the surface of Pd, which introduces an alternative reaction pathway with a lower activation energy.

5H2O2(aq) + 2MnO4- + 6H+(aq) → 2Mn2+(AQ) + 8H2O(l) + 5O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) Which element is being oxidized during the titration, and what is the element's change in oxidation number?

Oxygen, which changes from -1 to 0

A sample containing atoms of C and F was analyzed using x-ray photoelectron spectroscopy. The portion of the spectrum showing the 1s peaks for atoms of the two elements is shown above. Which of the following correctly identifies the 1s peak for the C atoms and provides an appropriate explanation?

Peak Y, because F has a greater nuclear charge than C has.

A student studied the kinetics of the reaction represented above by measuring the concentration of the reactant, X, over time. The data are plotted in the graph below. Which of the following procedures will allow the student to determine the rate constant, k , for the reaction?

Plot ln [X] versus time and determine the magnitude of the slope.

Consider the following potential energy vs. internuclear distance plot for the interaction between a cation and an anion. At which of the four labeled points on the graph are the repulsive forces greater than the attractive forces?

Point w

NO2(g) + CO(g) → NO(g) + CO2(g) The reaction between NO2(g) and CO(g) is represented above. The elementary steps of a proposed reaction mechanism are represented below. Step 1: 2 NO2(g) → NO(g) + NO3(g) (slow) Step 2: NO3(g) + CO(g) → NO2(g) + CO2(g) (fast) Which of the following is the rate law for the overall reaction that is consistent with the proposed mechanism?

Rate = k [NO2]2

2H2(g) + 2NO(g) ---> N2(g) + 2H2O(g) Step 1: 2NO(g) ↔ N2O2(g) (fast equilibrium) Step 2: N2O2(g) + H2(g) → N2O(g) + H2O(g) (slow) Step 3: N2O(g) + H2(g) → N2(g) + H2O(g) (fast) Which of the following initial rate law expressions is consistent with this proposed mechanism?

Rate = k[H2][NO]2

The data from a study of the decomposition of NO2(g) to form NO(g) and O2(g) are given in the table above. Which of the following rate law consistent with the data?

Rate = k[NO2]2

2 NOBr(g) → 2 NO(g) + Br2(g) The equation above represents an elementary step in a chemical reaction. Which of the following is the correct expression for the rate law of the elementary step?

Rate = k[NOBr]2

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.

What is the molecular geometry of CS32- ?

Trigonal Planar

A 1.0 L sample of a pure gas is found to have a lower pressure than that predicted by the ideal gas law. The best explanation for the observation is that the molecules of the gas

are attracted to each other and do not exert as much force on the container walls as they would if they had no mutual attractions

If a central atom is bonded to each of two sulfur atoms by double bonds, what must be the hybridization of the carbon atom?

sp

A molecule has bent molecular geometry. The hybridization on the central atom must be

sp2 or sp3