Advanced Placement Chemistry Multiple Choice Spanning 2014 to 2018 (2014-2018)
26. The O2(g) produced from the decomposition of the 1.0 L sample of H2O2(aq) is collected in a previously evacuated 10.0 L flask at 300. K. What is the approximate pressure in the flask after 400. s? (For estimation purposes, assume that 1.0 mole of gas in 1.0 L exerts a pressure of 24 atm at 300. K.)
(A) 1.2 atm
39. If equal masses of the following compounds undergo complete combustion, which will yield the greatest mass of CO2 ?
(A) Benzene, C6H6
13. The exothermic dissolution of Mg(OH)2(s) in water is represented by the equation above. The Ksp of Mg(OH)2 is 1.8 ¥ 10-11. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?
(A) Decreasing the pH
1. 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.
14. The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate. Which of the following explains why the slope of segment T is greater than the slope of segment R ?
(A) The specific heat capacity of the gaseous ethanol is less than the specific heat capacity of liquid ethanol.
36. When Reaction 3 occurs, does the hybridization of the carbon atoms change?
(A) Yes; it changes from sp to sp2 .
The process of dissolution of NaCl(s) in H2O(l) is represented in the diagram above. Which of the following summarizes the signs of (delta)H and (delta)S for each part of the dissolution process.
(ANSWERS ARE IN A TABLE) Positive for both H and S in solvent-solvent and solute-solute. Neg for both H and S in solute solvent interactions
20. Which of the following is the balanced net-ionic equation for the reaction between Li(s) and water?
(B) 2 Li(s) + 2 H2O(l) → 2 Li+(aq) + 2 OH−(aq) + H2(g)
19. On the basis of the pH curve, the pKa value of the acid is closest to
(B) 5
37. The acid-dissociation constants of HC3H5O3(aq) and CH3NH3+(aq) are given in the table above. Which of the following mixtures is a buffer with a pH of approximately 3 ?
(B) A mixture of 100. mL of 0.1 M HC3H5O3 and 50. mL of 0.1 M NaOH
30. Which of the following accounts for the observation that the pH of pure water at 37°C is6.8?
(B) At 37∞C the autoionization constant for water, Kw , is larger than it is at 25∞C.
12. 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) B, because it has three valence electrons
44. The proposed mechanism can be written in a more general form, as shown above. Species other than Cl can also decompose O3 through the same mechanism. Which of the following chemical species is most likely to decompose O3 in the upper atmosphere through the above mechanism?
(B) Br
11. The molecular formula and molar mass of two straight-chain hydrocarbons are listed in the table above. Based on the information in the table, which compound has the higher boiling point, and why is that compound's boiling point higher?
(B) C4H10 , because it has more electrons, resulting in greater polarizability and stronger dispersion forces
32. A sample of a compound that contains only the elements C, H, and N is completely burned in O2 to produce 44.0 g of CO2 , 45.0 g of H2O, and some NO2 . A possible empirical formula of the compound is
(B) CH5N
28. The reaction is thermodynamically favorable. The signs of ΔG° and ΔS° for the reaction are which of the following?
(B) G is neg, S is pos
38. The Lewis electron-dot diagrams of the HClO3 molecule and the HClO2 molecule are shown above at the left and right, respectively. Which of the following statements identifies the stronger acid and correctly identifies a factor that contributes to its being the stronger acid?
(B) HClO3(aq) is the stronger acid because the additional electronegative oxygen atom on the chlorine atom stabilizes the conjugate base.
40. The reaction system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system?
(B) Lowering the temperature of the system
42. Which of the following rate laws for the overall reaction corresponds to the proposed mechanism?
(B) Rate = k[Cl][O3]
22. Acid-dissociation constants of two acids are listed in the table above. A 20. mL sample of a 0.10 M solution of each acid is titrated to the equivalence point with 20. mL of 0.10 M NaOH. Which of the following is a true statement about the pH of the solutions at the equivalence point?
(B) Solution 1 has a higher pH at the equivalence point because CH3CO2H has the stronger conjugate base.
18. 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) ?
(B) Some gas will be produced but less than the amount of gas produced with Li(s).
8. At 127°C, the entire sample of I2 is observed to have vaporized. How does the mass of vessel 5 at 127°C compare to its mass at 27°C?
(B) The mass is the same, since the number of each type of atom in the vessel is constant.
24. The reaction between NO(g) and O2(g) to produce NO2(g) in a rigid reaction vessel is represented in the diagram above. The pressure inside the container is recorded using a pressure gauge. Which of the following statements correctly predicts the change in pressure as the reaction goes to completion at constant temperature, and provides the correct explanation?
(B) The pressure will decrease because there are fewer molecules of product than of reactants.
27. Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?
(B) The reaction is first order if the plot of ln [H2O2] versus time is a straight line.
The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?
(B) The reaction will form more reactant.
45. A solution of a salt of a weak acid HY is added to a solution of another weak acid HX. Based on the information given above, which of the following species is the strongest base?
(B) Y−(aq)
35. Reaction 2 occurs when an excess of 6 M HCl(aq) solution is added to 100. mL of NaOCl(aq) of unknown concentration. If the reaction goes to completion and 0.010 mol of Cl2(g) is produced, then what was the molarity of the NaOCl(aq) solution?
(C) 0.10 M
7. At 127°C, the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation?
(C) 2 NaHCO3(s) Æ Na2CO3(s) + CO2(g) + H2O(g)
6. A hot iron ball is dropped into a 200.g sample of water initially at 50.° C. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature of the water? (The specific heat of water is 4.2 J/(g·°C).)
(C) 60.°C
5. 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?
(C) Hydrogen bond
2. The lattice energy of a salt is related to the energy required to separate the ions. For which of the following pairs of ions is the energy that is required to separate the ions largest? (Assume that the distance between the ions in each pair is equal to the sum of the ionic radii.)
(C) Mg2+(g) and O2−(g)
25. Which of the following identifies the element(s) being oxidized and reduced in the reaction?
(C) Oxygen is both oxidized and reduced.
41. To maximize the yield in a certain manufacturing process, a solution of a weak monoprotic acid that has a concentration between 0.20 M and 0.30 M is required. Four 100. mL samples of the acid at different concentrations are each titrated with a 0.20 M NaOH solution. The volume of NaOH needed to reach the end point for each sample is given in the table above. Which solution is the most suitable to maximize the yield?
(C) Solution C
23. A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water, and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g⋅°C).)
(C) The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.
17. Which of the following changes will most likely increase the rate of reaction between Li(s) and water?
(C) Using a 0.35 g sample of Li(s) cut into small pieces
46. A 1.0 mol sample of X(g) and a 1.0 mol sample of Q(g) are introduced into an evacuated, rigid 10.0 L container and allowed to reach equilibrium at 50°C according to the equation above. At equilibrium, which of the following is true about the concentrations of the gases?
(C) [R] = [Z] > [Q]
31. 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?
(D) Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions
10. An acetate buffer solution is prepared by combining 50. mL of 0.20 M acetic acid, HC2H3O2(aq), and 50. mL of 0.20 M sodium acetate, NaC2H3O2(aq). A 5.0 mL sample of 0.10 M NaOH(aq) is added to the buffer solution. Which of the following is a correct pairing of the acetate species present in greater concentration and of the pH of the solution after the NaOH(aq) is added? (The pKa of acetic acid is 4.7.)
(D) C H O - > 4.7
34. Ca(OH)2 (s) precipitates when a 1.0 g sample of CaC2 (s) is added to 1.0 L of distilled water at room temperature. If a 0.064 g sample of CaC2(s) (molarmass64g/mol)isusedinstead and all of it reacts, which of the following will occur and why? (The value of Ksp for Ca(OH)2 is 8.0 108.)
(D) Ca(OH)2 will not precipitate because Q < Ksp .
The dissociation of the weak acid HF in water is represented by the equation above. Adding a 1.0 mL sample of which of the following would increase the percent ionization of HF(aq) in 10mLofasolutionof1.0M HF?
(D) Distilled water
15. A solution is prepared by mixing 50 mL of 1 M NaH2PO4 with 50 mL of 1 M Na2HPO4. On the basis of the information above, which of the following species is present in the solution at the lowest concentration?
(D) PO43−
3. 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?
(D) The atomic mass of X is between 90 and 92.
21. 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?
(D) There are dipole-induced dipole and London dispersion interactions between water and benzene.
49. 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?
(D) Y is more polar than X.
48. In trial 2 which of the reactants would be consumed more rapidly, and why?
(D) Y, because the rate of disappearance will be double that of X.
Which of the following statements about (delta)H for the reaction is correct
(delta)H>0 because energy is required to break the N-N bond
Based on the values of ^G for the three reactions represented above, what is the value of ^G for the reaction represented below?
-1320kJ/molrxn
In an experiment a student mixes a 50.0mL sample of 0.100M AgNO3 with a 50.0mL sample of 0.100M NaCl at 20.0 C in a coffee cup calorimeter. Which of the following is the enthalpy change of the precipitation reaction represented above if the final temperature of the mixture is 21.0C
-84.0kJ/molrxn
What is the value of the enthalpy change per mole of HCl(g) produced?
-93 kJ
The temperature of the CH3OH (l) is increased from 300K to 400K to vaporize all the liquid, which increases the pressure in the vessel to 0.30atm. The experiment is repeated under identical conditions but this time using half the mass of CH3OH that was used originally. What will be the pressure in the vessel at 400K?
0.15atm
The value of Kp for the evaporation of CH3OH (l) at 300K is closest to
0.2
If 3.80g of Cu3(PO4)2 was recovered from step 1, what was the approximate {Cu2+} in the original solution? The molar mass of Cu3(PO4)2 is 381g/mol
0.30M
Based on the thermodynamic data, which of the following is true at 298 K?
0<Keq<1
The pH of a solution made by combining 150.mL of 0.10M KOH (aq) with 50.0 mL of 0.20 M HBr is closest to which of the following?
12
A 0.0300 mol sample of NO2 (g) is placed in a rigid 1.00 L reaction vessel and allowed to reach equilibrium at a certain temperature. What is the value of Kc at this temperature if 0.00500 mol of N2O4 (g) is present at equilibrium?
12.5
HCHO2 (aq), a weak acid (Ka=2 * 10^-4), dissociates in water according to the equation above. Which of the following provides the best estimate of the pH of 0.5M HCHO2 and identifies the species at the highest concentration (excluding H2O) in the solution?
2
N2O4(g)<-> 2NO2 Kp=3.0 at 70C colorless brown A mixture of NO2(g) and N2O4(g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above. If P(N2O4) is 1.33 atm when the system is at equilibrium at 70C which is P(NO2)?
2.0 atm
On the basis of the information above, what is the appropriate percent ionization of HNO2 in a 1.0M HNO2 solution?
2.0%
When the 4.0L of He(g), 6.0 L of N₂(g) and 10 L of Ar(g), all at 0C and 1 atm, are pumped into an evacuated 8.0L rigid container, the final pressure in the container is 0C.
2.5 atm
When the 5.0g of NH4ClO4(d) is added to 100 mL of water in a calorimeter, the temperature of the solution formed decreases by 3.0C. If 5.0g of NH4ClO4(s) is added to 1000 mL of water in calorimeter initially at 25C, the final temperature of the solution will be approximately
24.7C
When 70g of Li3N (s) (molar mass 35g/mol) reacts with excess H2 (g), 8.0g of LiH (s) is produced. The percent yield is closest to
25%
(BOND ENERGIES ARE GIVEN) Based on the bond energies listed in the table above, which of the following is closest to the bond energy of the C-N bond?
300 kJ/mol
The students determined that the reaction produced 0.010 mol of Cu(NO3)2. Based on the measurement, what has the percent of Cu by mass in the original 2.00 g sample of the mixture?
32%
Which of the following particulate representations shows a process during which the entropy of the system decreases?
4 (mickey mouse ear) pairs ----> all molecules touching
Which of the following particle diagrams best represents the products when four molecules of H2O2 (l) decompose into water and oxygen gas at room temperature?
4 pairs of 2 hydrogen/1 oxygen, 2 pairs of hydrogen
Fe³⁺ (aq) +KSCN(s)->FeSCN²⁺(aq)+K⁺(aq) To determine the moles of Fe3+(aq) in a 100mL sample of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species, FeSCN2+(aq), as represented by the equation above. The absorbance of FeSCN2+(aq) a different concentration is shown in the graph to the right. (IMAGE) 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.)
4 x 10⁻⁶
4. Which of the following diagrams best depicts an alloy of Ni and B ?
A
9. The gas particles in vessel 3 at 27°C are represented in the diagram above. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles when vessel 3 is heated to 127°C?
A
Which of the following best describes the change that takes place immediately after the CH3OH (l) is introduced into the previously evacuated vessel?
A physical change takes place because intermolecular attractions are overcome
47. The potential energy of a system of two atoms as a function of their internuclear distance is shown in the diagram above. Which of the following is true regarding the forces between the atoms when their internuclear distance is x ?
A) The attractive and repulsive forces are balanced, so the atoms will maintain an average internuclear distance x.
NH3 reacts with BF3 to form a single species. Which of the following structural diagrams is the most likely representation of the product of the reaction?
ALL ANSWERS ARE DIAGRAMS. Chose the one with N and B in the middle, surrounded by H and F
A particle view of a sample of H2O2(aq) is shown to the right. The H2O2(aq) is titrated with KMnO4(aq), as represented by the equation below. (IMAGE AND EQUATION IM TOO LAZY TO TYPE) Which of the following particle views best represents the mixture when the titration is halfway to the equivalence point?
ALL ANSWERS ARE IMAGES Correct image has 5 H2O2 and, 2 Mn2+
ClO2-(aq)+HCOOH(aq)<-> HClO2(aq)+HCOO-(aq) Keq<1 What are the relative strengths of the acids and bases in the reaction represented by the equation above?
Acid Strength= HClO2>HCOOH Base Strength=ClO2-<HCOO-
Dissolution of the slightly soluble salt, CaF2, is shown above. Which of the following changes will decrease [Ca2+] in a saturated solution of CaF2 and why?
Adding some NaF because the reaction will proceed toward the reactants
(2 equations given with Keq) Equal volumes of 0.1 M AgNO3(aq) and 2.0 M NH3(aq) are mixed and the reactions represented above occur, which Ag species will have the highest concentration in the equilibrium system shown below and why? Ag⁺(aq)+2NH3(aq)<-> Ag(NH3)2⁺(aq) Keq3=?
Ag(NH3)2⁺(aq), because Keq3=1.6E7
The first ionization energy of an element is the energy required to remove an electron from a gaseous atom of the element (i.e. X(g)--> (X^+(g)+e-). The values of the first ionization energies for the third row elements are shown in the graph above. On the basis of the information give, which of the following reactions is exothermic? (IMAGE)
Al(g)+Mg+(g)->Al+(g)+Mg(g)
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?
All answers are pictures. Chose the one that has 4 of 3 atoms together and 1 of 2 atoms together
29. Assume that the bond enthalpies of the oxygen- hydrogen bonds in H2O are not significantly different from those in H2O2 . Based on the value of ΔH° of the reaction, which of the following could be the bond enthalpies (in kJ/mol) for the bonds broken and formed in the reaction?
B
43. Which of the following reaction energy profiles best corresponds to the proposed mechanism?
B
In the reaction represented above, what is the hybridization of the C atoms before and after the reaction occurs?
Before=sp² After= sp³
Which of the following Lewis electron-dot diagrams represents the molecule that is the most polar?
Br-----F
The compound CCl4 is nonflammable and was once commonly used in fire extinguishers. On the basis of periodic properties, which of the following compounds can most likely be used as a fire resistant chemical?
CBr4
When a small amount of 12M HNO3 is added to a buffer solution made by mixing CH3NH2 and CH3NH3Cl, the pH of the buffer solution changes from 10.64 to 10.62. Which of the following equations represents the reaction that accounts for the fact that the pH does not change significantly when the HNO3 is added?
CH3NH2(aq) + H+ ----> CH3NH3+ (aq)
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
CaCl2 with twice the molarity of the solution in vessel 1
2H2O2(l)->2H2O(l)+O2(g) The exothermic process represented above is best classified as a
Chemical change because covalent bonds are broken and new covalent bonds are formed
Based on structures shown above, (IMAGE) which of the following statements identifies the compound with the highest boiling point and provides the best explanation for the higher boiling point?
Compound 2, because it forms hydrogen bonds, whereas compound 1 does not.
50. 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?
D
The standard reduction potentials for the half reactions related to the galvanic cell represented above are listed in the table below
E cell = +0.20V
(Half reactions are given) Based on the formation in the table above, which of the following shows that the cell potential and Gibbs free energy change for the overall reaction that occurs in a standard galvanic cell?
E=+1.63 G=-944
The complete photoelectron spectra of neutral atoms of two unknown elements, X and Y, are shown above. (IMAGE) Which of the following can be inferred from the data?
Element Y has a greater nuclear charge than element X does.
The Maxwell-Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature shown to the left. Which gas has the greater molar mass?
Gas A
Which of the following happens to H atoms in the forward reaction?
H atoms are both oxidized and reduced
A student prepares a solution by combining 100 mL of 0.30 M HNO3(aq) and 100 mL of 0,30 M KNO2(aq). Which of the following equations represents the reaction that best helps to explain why adding a few drops of 1.0 M HCl(aq) does not significantly change the pH of the solution?
H+(aq)+NO2-(aq)->HNO2(aq)
Which of the following has the bonds arranged in order of decreasing polarity?
H-F>N-F>F-F
A 20mL sample of 0.50 M HC2H3O2 (aq) is titrated with 0.50M NaOH. Which of the following best represents the species that react and the species produced in the reaction?
HC2H3O2(aq) + OH- ---> H2O (l) + C2H3O2- (aq)
Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?
HF, because its molecules form hydrogen bonds
Cu(S)+ 4HNO3(aq)-->Cu(NO3)2(aq)+2NO2(g)+2H2O(l) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in 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, indication the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. Which of the following is true about the reaction?
It is a redox reaction, because Cu(s) is oxidized and the nitrogen atom in NO3-(aq) is reduced
Which of the following most likely describes the solid represented in the diagram to the left?
It is brittle, water soluble electrolyte that is a poor thermal and electrical conductor as a solid.
Two molecules of the amino acid glycine join through the formation of a peptide bond, as shown above. The thermodynamic data for the reaction are listed in the following table (IMAGE AND TABLE) Under which of the following temperature conditions is the reaction thermodynamically favored?
It is not favored at any temperature
Which of the following shows the relationship between K1 and K2 in the reactions represented above?
K2 = 1/(K1)^2
(REACTION TABLE WITH Keq GIVEN) Based on the information above, which of the following expressions represents the equilibrium constant, K, for the reaction represented by the equation below? La³⁺+CO₃²⁻<-> LaCO₃⁺
K=(K1)(Kw)/Ka
The forward reaction is thermodynamically favored at which of the following temperatures?
Low temperatures only
Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(l) is a good conductor of electricity?
MgO(s) consists of separate Mg2+ ions and O2- ions held in a fixed lattice, but in MgO(l) the ions are free to move and conduct electricity.
Equimolar samples of each of three gases, H2, I2, and HI are introduced into a 3.0L container that is heated to 600C. According to the information above, which of the following will occur as the system approaches equilibrium?
More HI will be produced because Q<Kc
On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water.
NH3
Three substances were studied in the laboratory and the data in the table above were collected. Based on the data, which of the following shows the type of bonding in each substance?
Network Covalent (X), Metallic (Y), Ionic (Z)
Which of the following best predicts how the partial pressures of the reacting species will be affected if a small amount of Ar(g) is added to the equilibrium mixture at constant volume?
No change will take place
The ideal gas law best describes the properties of which of the following gases at 0C and 1 atm?
N₂
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?
O in top left corner on N ----> colliding into O
O3(g)+O(g)->2O2(g) The decomposition of O3(g) in the upper atmosphere is represented by the equation above. The potential energy diagram for the decomposition of O3(g) in the presence and absence of NO(g) is given below. (IMAGE) 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
The rate of the reaction represented above increases significantly in the presence of P (s). Which of the following best explains this observation?
One of the reactants binds on the surface of P(s), which introduces an alternative reaction pathway with a lower activation energy
For which of the equilibrium systems represented below will the amount of products at equilibrium increase if the volume of the reaction vessel is increased at a constant temperature?
PCl5 <----> PCl3 + Cl2
The values of dissociation constants for H3PO4 are given in the table to the left. Given that the solution in the beaker at the end of step 2 had a pH of approximately 1, which of the following chemical species had the lowest concentration among the products of step 2?
PO4 ^3-
Equimolar samples of Pb(OH)2, PbI2, and PbF2 are placed in three separate beakers, each containing 250mL of water at 25C. After the solutions are stirred, solid remains in the bottom of each beaker. Based on the Ksp values for the compounds listed in the table below, a solution of which of the compounds will have the lowest [Pb2+] ?
Pb(OH)2 (s)
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
Based on the information in the table to the left, which of the compounds has the highest boiling point, and why?
Propanoic acid, because it can form intermolecular hydrogen bonds
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 mechanism are represented below. Step 1: 2NO2(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
(4 reactions are given, A-D) The reactions represented above are carried out in sealed, rigid container and allowed to reach equilibrium. If the volume of each container is reduced from 1.0 L to .5 L at constant temperature, for which of the reactions will the amount of products be increased
Reaction A
The step-wise dissociation of selenous acid, H2SeO3 (aq), is represented by the equations above. Which of the following best helps explain why the value of Ka2 is so much smaller than the value of Ka1?
Removing the first H+ from H2SeO3 requires less energy than removing the second H+. because the second H+ is removed from a negatively charged species.
Based on coulomb's law and the information in the table above, which of the following anions is most likely to have the strongest interaction with nearby water molecule in an aqueous solution?
S2-
If a pure sample of an oxide of sulfur contains 40 percent sulfur and 60 percent oxygen by mass, then the empirical formula of the oxide is
SO₃
The masses of carbon and hydrogen in samples of four pure hydrocarbons are given to the left. The hydrocarbon in which sample has the same empirical formula as propene, C3H6?
Sample B (72g carbon, 12g hydrogen)
The mass of the Cu (s) produced in step 3 was slightly more than the mass predicted from the 3.80 g Cu3(PO4)2 recovered from step 1. Which of the following could account for the discrepancy in the yield of Cu from step 3?
Some unreacted Zn (s) was mixed in with the Cu(s)
Which of the following experimental techniques will allow the most accurate determination of the concentration of NO2(g) at equilibrium ?
Spectrophotometry
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?
Testing the electrical conductivity of an aqueous solution of the substance
Which of the following best helps to explain why CCl4 is a liquid whereas CI4 is a solid when both are at 25C
The London dispersion forces are stronger in CI4 than in CCL4 because CI4 has a more polarizable electron cloud than CCl4
Based on the data above, what can be concluded regarding the strength of the C-H, N-H, and O-H bonds in the molecules shown?
The O-H bond is the strongest
(Table shoes type of steel and characteristics) The table above provides some information about two types of steel, both of which are alloys of iron and carbon. Which of the following best helps to explain why high-carbon steel is more rigid than low carbon steel?
The additional carbon atoms within the allow make it more difficult for the iron atoms to slide past one another.
3O2(g)<->2O3(g) Kc=1.8E-56 at 570 K For the system represented above, [O2] and [O3] initially are 0.150 mol/L and 2.5 mol/L respectively. which of the following best predicts what will occur as the system approaches equilibrium at 570 K?
The amount of O3(g) will decrease, because Q>Kc
Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?
The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does
Which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath.
The forward reaction is endothermic
Cl-(aq)+CLO-(aq)+2H(aw)->CL2(g) +H2O(l) What effect will increasing [H+] at constant temp have on the reaction represented above?
The frequency of collisions between H+(aq) ions and ClO- (aq) ions will increase.
A 50.0g of Fe (s) at 100C is added to 500mL of water at 35C in a perfectly insulated container. Which of the following statements is true?
The heat energy lost by the Fe will be equal to the heat energy gained by the water
Cr2O7² ⁻(aq) + H2O (l)<->2CrO4² ⁻(aq)+2H3O+(aq) orange yellow The equilibrium system represented by the equation above initially contains equal concentrations of Cr2O7² ⁻(aq) and 2CrO4² ⁻(aq). Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH(aq) to the system and provides an explanation?
The mixture will become more yellow because OH-(aq) will shift the equilibrium toward products
Which of the following is the most likely reason that the reaction occurs at a significant rate only if the temperature of the reaction mixture is greater than 200C?
The reaction has a high activation energy
2H2(g)+O2(g)->H2O(g) When H2(g) and O2(g) are mixed together in a rigid reaction vessel at 25C, no reaction occurs. When the mixture is sparked, however, the gases react vigorously according to the equation above, releasing heat. Which of the following statements correctly explains why the spark is needed for the reaction to occur when the gases are originally at 25C?
The reaction has a large activation energy at 25C
A sample of a solid labeled as NaCL may be impure. A student analyzes the sample and determines that it contains 75 percent chlorine by mass. Pure NaCl(s) contains 61 percent chlorine by mass. Which of the following statements is consistent with the data?
The sample contains NaCl(s) and LiCl(s)
(TABLE) 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 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?
The student labelled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentrations
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 students used a 1.5 M solution of HNO3(aq) instead of 15.8 M solution of HNO3(aq)
H2(g)+Cl2(g)<->2HCl(g) Kp=2E30 at 298 K HCl(g) can be synthesized from H2(g) and Cl2(g) as represented above. A student studying the kinetics of the reaction proposes the following mechanism. (3 steps listed out, too tired to type them, sorry) Which of the following statements identifies the greatest single reason that the value of Kp for the overall reaction at 298 K has such a large magnitude?
The value of (delta) H for the overall reaction is large and negative
A balloon filled with 0.25 moles He (g) at 273K and 1.0 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 220K and the air pressure is 0.10atm?
The volume will increase because the decrease in air pressure will have a greater effect than the decrease in temperature
The ionization energies of an unknown element, X, are listed in the table to the left. Which of the following is the most likely empirical formula of a compound formed from element X and phosphorus, P?
X3P2
(ANOTHER TABLE GIVEN) Three saturated solutions (X,Y, and Z) are prepared at 25C. Based on the information in the table above, which of the following lists the solutions in order of increasing [Ag+]?
Z<X<Y
(IMAGE) The mass spectrum of an average sample of a pure element is shown in the figure above. Which of the following is the identity of the element?
Zr
A mixture of NO2 (g) and N2O4 (g) is at equilibrium in a rigid reaction vessel. If the temperature of the mixture is decreased then
[N2O4] will increase and the mixture will turn a lighter brown
Based on the bond energies shown in the table above, which of the following diagrams best represents the change in energy as the reaction represented below proceeds? a. b. c. d.
a.
The distribution of speeds of H2 (g) molecules at 273 K and 1 atm is shown in the diagram above. Which of the following best shows the speed distribution of He (g) atoms under the same conditions of temperature and pressure a. b. c d.
a.
Which of the following diagrams best illustrates how a displacement in an ionic crystal results in clevage and brittleness? a. b. c. d.
a.
Which of the following diagrams best represents the AgNo3 solution before the reaction occurs? a. b. c. d.
a.
A student mixes a 10.0 mL sample of 1.0 M NaOH (aq) with a 10.0 mL sample of 1.0 M HCl (aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0 degrees C. If the final temperature of the mixture is 26.0 degrees C, what is the experimental value of delta H rxn? (Assume that the solution mixture has a specific heat of 4.2 J/(gK) and a density of 1.0 g/mL) a. -50. kJ/mol rxn b. -25 kJ/mol rxn c. -5.0 x 10^4 kJ/mol rxn d. -5.0 x 10^2 kJ/mol rxn
a. -50. kJ/mol rxn
When 200 mL of 2.0 NaOH (aq) is added to 500 ML of 1.0M HCl (aq), the PH of the resulting mixture is closest to a. 1.0 b. 3.0 c. 7.0 d. 13.0
a. 1.0
On the basis of the data provided above, the gas in container 3 could be a. CH4 b. O2 c. Ar d. CO2
a. CH4
On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity? a. CH4 < SiCl4 < SF4 b. CH4 < SF4 < SiCl4 c. SF4 < CH4 < SiCl4 d. SiCL4 < SF4 < CH4
a. CH4 < SiCl4 < SF4
Which of the following arranges the molecules N2, O2, and F2 in order of their bond enthalpies, from least to greatest? a. F2 < O2 < N2 b. O2 < N2 < F2 c. N2 < O2 < F2 d. N2 < F2 < O2
a. F2 < O2 < N2
The potential energy as a function of inter-nuclear distance for three diatomic molecules, X2, Y2, and Z2, is shown in the graph above. Based on the data in the graph, which of the following correctly identifies the diatomic molecules, X2, Y2, and Z2 a. H2, N2, O2 b. H2, O2, N2 c. N2, O2, H2 d. O2, H2, N2
a. H2, N2, O2
2 H2S (g) + CH4 (g) -> <- CS2 (g) + 4 H2 (g) Ke= 3.4 x 10^-4 A 0.10 mol sample of each of the four species in the reaction represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest concentration when the system reaches equilibrium? a. H2S (g) b. CH4 (g) c. CS2 (g) d. H2 (g)
a. H2S (g)
HX (aq) + Y- (aq) -> <- HY (aq) + X- (aq) Keq>1 a. HX (aq) b. Y- (aq) c. HY (aq) d. X- (aq)
a. HX (aq)
Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl-] a. PbCl2 b. CuCl c. AgCl d. Hg2Cl2
a. PbCl2
Under the conditions given, consider containers 1, 2, and 4 only. The average speed of gas particles is a. greatest in container 1 b. greatest in container 2 c. greatest in container 4 d. the same in containers 1, 2 and 4
a. greatest in container 1
Which of the following best explains why more energy is required for the process occurring at 110 K than for the process occurring at 90 K? a. intermolecular attractions are completely overcome during vaporization b. intermolecular attractions in the solid phase are weaker than in the liquid phase c. electron clouds of methan molecules are less polarizable at lower temperatures d. vaporization involves a large increase in temperature
a. intermolecular attractions are completely overcome during vaporization
A sample of hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance? a. ionic bonds b. metallic bonds c. covalent bonds d. hydrogen bonds
a. ionic bonds
The enthalpy of vaporization of water is 40.7 kJ/mol. Which of the following best explains why the enthalpy of vaporization of methane is less than that of water? a. methane does not exhibit hydrogen bonding, but water does b. methane has weaker disperision forces c. methane has a smaller molar mass d. methane has a much lower density
a. methane does not exhibit hydrogen bonding, but water does
In the reaction represented above, the number of MnO4- ions that react must be equal to which of the following? a. one-fifth the number of Fe2+ ions that are consumed b. eight times the number of H+ ions that are consumed c. Five times the number of Fe3+ ions that are produced d. one-half the number of H2O molecules that are produced
a. one-fifth the number of Fe2+ ions that are consumed
Which element is being oxidized during the titration, and what is the element's change in oxidation number? a. oxygen, which changes from -1 to 0 b. oxygen, which changes from 0 to -2 c. manganese, which changes from -1 to +2 d. manganese, which changes from +7 to +2
a. oxygen, which changes from -1 to 0
Which of the following statements about the bonds in the reactants and products is more accurate? a. the sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products b. the sum of the bond enthalpies of the bonds in the reactant is less than the sum of the bond enthalpies of the bonds in the products c. the length of the bond between carbon and oxygen in CH3OH is shorter than the length of the bond between carbon and oxygen in CO d. all of the bonds in the reactant and products are polar
a. the sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products
A 10. g cube of copper at a temperature T1 is placed in an insulated cup containing 10. g of water at a temperature T2. If T1 > T2, which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J/(g C) and the specific heat of water is 4.18 J/(g C) a. the temperature of the copper changed more than the temperature of the water b. the temperature of the water changed more than the temperature of the copper c. the temperature of the water and the copper changed by the same amount d. the relative temperature changes of the copper and the water cannot be determined without knowing T1 and T2
a. the temperature of the copper changed more than the temperature of the water
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
Steel is an alloy consisting of Fe with a small amount of C. Elemental Cr can be added to steel to make the steel less likely to ruse; Cr atoms react with oxygen in the air to form a nonreactive layer of chromium oxide on the surface of the steel, preventing the oxidation of underlying Fe atoms. A sample of steel-chromium alloy contains 15 percent Cr by mass. Which of the following diagrams best shows a particle-level view of a surface section and an interior section of the alloy represented below at the left? a. b. c. d.
b.
How much energy is required to melt 64 g of methane at 90 K? (the molar mass of methane is 16 g/mol) a. 0.24 kJ b. 3.8 kJ c. 33 kJ d. 60. kJ
b. 3.8 kJ
Which of the following best describes the flow of heat when 1.0 mol of XY2 decomposes? a. 50 kJ of heat is transferred to the surroundings b. 50 kJ of heat is transferred from the surroundings c. 100 kJ of heat is transferred to the surroundings d. 100 kJ of heat is transferred from the surroundings
b. 50 kJ of heat is transferred from the surroundings
A 23.0g sample of a compound contains 12.0 g of C, 3.0g of H, and 8.0g of O. Which of the following is the empirical formula of the compound? a. CH3O b. C2H6O c. C3H9O2 d. C4H12O2
b. C2H6O
Which of the following molecules is least soluble in water? a. b. c. d.
b. CCl4
Based on the information in the table above, which liquid, CS2 (l) or CCl4 (l), has the higher equilibrium vapor pressure at 25 degrees C, and why? a. CS2 (l), because it has stronger London dispersion forces b. CS2 (l), because it has weaker London dispersion forces c. CCl4 (l), because it has stronger London dispersion forces d. CCl4 (l), because it has weaker London dispersion forces
b. CS2 (l), because it has weaker London dispersion forces
M+ is an unknown metal cation with a +1 charge.... mixes AgNO3 solution, causing AgCl to precipitate What is the identity of the metal chloride? a. NaCl b. KCl c. CuCl d. LiCl
b. KCl
According to the information in the table above, a 1.00g sample of which of the following contains the greatest mass of oxygen? a. Na2O b. MgO c. K2O d. CaO
b. MgO
Which of the following Lewis electron-dot diagrams represents the molecule that contains the smallest bond angle? a. b. c. d.
b. NF3
2 NO2 (g) + F2 (g) -> 2 NO2F (g) The rate law for the reaction represented by the equation above is rate= k[NO2][F2]. Which of the following could be the first elementary step of a two-step mechanism for the reaction if the first step is slow and the second step is fast? a. F2 (g) -> 2 F (g) b. NO2 (g) + F2 (g) -> NO2F (g) + F (g) c. NO2 (g) + F (g) -> NO2F (g) d. 2 NO2 (g) + F2 (g) -> 2NO2F (g)
b. NO2 (g) + F2 (g) -> NO2F (g) + F (g)
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. Ca 2+ d. In 3+
b. Na+
At the point labeled R on the pH curve, which of the following ions are present in the reaction mixture at a concentration greater than 0.10 M? a. Na+ and Cl- only b. Na+, Cl-, and H+ only c. Na+, Cl-, and OH- only d. Na+, Cl-, H+, and OH-
b. Na+, Cl-, and H+ only
Which of the following could be the identity of a which crystalline solid that exhibits the following properties? -it melts at 320 degrees 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. NaOH (s)
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 show above. Which of the following correctly identifies the 1s peak for the F atoms and provided an appropriate an appropriate explanation? a. Peak X, because F has a smaller firs ionization energy than C has b. Peak X, because F has a greater nuclear charge than C has c. Peak Y, because F is more electronegative than C is d. Peak Y, because F has a smaller atomic radius than C has
b. Peak X, because F has a greater nuclear charge than C has
A student conducted an experiment to determine delta H rxn for the reaction between HCl (aq) and NaOH (aq). The student ran two trials using the volumes of HCl (aq) and NaOH (aq) indicated in the table above, and determined the amount of heat released. Which of the following best explains the relationship between X and Y? a. Y=2X, because the volume of HCl (aq) used in trial 2 is twice the volume used in trial 1 b. Y=X, because the number of moles of acid and base reacting with each other is the same in both trials c. Y=2X/3, because the heat is distributed over more particles in trial 2 and in trial 1 d. the relationship between X and Y cannot be predicted
b. Y=X, because the number of moles of acid and base reacting with each other is the same in both trials
A 1.0 mol sample of CO (g) and a 1.0 mol sample of H2 (g) are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 483 K. Which of the following is true at equilibrium? a. [H2] = 2[CO] b. [H2] < [CO] c. [CO] = [CH3OH] < [H2] d. [CO]= [CH3OH] = [H2]
b. [H2] < [CO]
Consider the reaction represented above at 298 K. When equal volumes of N2 (g) and H2 (g), each at 1 atm, are mixed in a closed container at 298 K, no formation of NH3 (g) is observed. Which of the following best explains the observation? a. the N2 (g) and the H2 (g) must be mixed in a 1:3 ratio for a reaction to occur b. a high activation energy makes the forward reaction extremely slow at 298 K c. the reaction has an extremely small equilibrium constant, thus almost no product will form d. the reverse reaction has a lower activation energy than the forward reaction, so the forward reaction does not occur
b. a high activation energy makes the forward reaction extremely slow at 298 K
C2H4 (g) + H2 (g) -> C2H6 (g) Which of the following will most likely increase the rate of the reaction represented above? a. decreasing the temperature of the reaction b. adding a heterogeneous catalyst to the reaction system c. increasing the volume of the reaction vessel using a piston d. removing some H2 (g) from the reaction system
b. adding a heterogeneous catalyst to the reaction system
The pH of a 0.01 M HNO2 (aq) solution is in which of the following ranges? (For HNO2 (aq), Ka= 4.0 x 10^-4) a. between 1 and 2 b. between 2 and 3 c. between 4 and 5 d. between 6 and 7
b. between 2 and 3
The table above shows the structural formula 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. butane < acetone < 1-propanol
At 1.0 atm a sample of ice is heated to liquid water and then to water vapor. The heating curve is shown in the graph above. Which of the following lists the signs for the changes in enthalpy and entropy for the process corresponding to segment X, going from left to right? a. delta H: positive // delta S: negative b. delta H: positive // delta S: negative c. delta H: negative // delta S: negative d. delta H: negative // delta S: positive
b. delta H: positive // delta S: negative
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. ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces
Consider the reaction represented by the equation 2X + 2Z -> X2Z2. During a reaction in which a large excess of reactant X was present, the concentration of reactant Z was monitored over time. A plot of the natural logarithm of the concentration of Z versus time is shown in the figure above. The order of the reaction with respect to reactant Z is a. zero order b. first order c. second order d. third order
b. first order
A mixture of CO (g) and H2 (g) is pumped into a previously evacuated 2.0 L reaction vessel. The total pressure of the reaction system is 1.2 atm at equilibrium. What will be the total pressure of the system if the volume of the reaction vessel is reduced to 1.0 L at constant temperature? a. less than 1.2 atm b. greater than 1.2 atm but less than 2.4 atm c. 2.4 atm d. greater than 2.4 atm
b. greater than 1.2 atm but less than 2.4 atm
What would be the effect on the reaction rate if the solution of C25H30N3+ (aq) is diluted by a factor of two? a. it would be higher b. it would be lower c. it would not change d. it would initially be higher but then rapidly decrease
b. it would be lower
Data collected during a titration of a 20.0 mL sample of a 0.10 M solution of a monoprotic acid with a solution of NaOH of unknown concentration are plotted in the graph above. Based on the data, which of the following are the approximate pKa of the acid and the molar concentration of the NaOh a. pKa: 4.7 // [NaOH]: 0.050 M b. pKa: 4.7 // [NaOH]: 0.10 M c. pKa: 9.3 // [NaOH]: 0.050 M d. pKa: 9.3 // [NaOH]: 0.10 M
b. pKa: 4.7 // [NaOH]: 0.10 M
The reaction represented above occurs in a single step that involves the collision between a particle of NO and a particle of NO3. A scientist correctly calculates the rate of collisions between NO and NO3 that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy? a. the energy of collisions between two reactant particles is frequently absorbed by collision with a third particle b. the two reactant particles must collide with a particular orientation in order to react c. the activation energy for a reaction is dependent on the concentrations of the reactant particles d. the activation energy for a reaction is dependent on the temperature
b. the two reactant particles must collide with a particular orientation in order to react
ON the basis of the information above, the dissolution of FeF2 (s) in acidic solution is a. thermodynamically favorable, because K2>1 b. thermodynamically favorable, because K3>1 c. not thermodymaically favorable, because K1 <1 d. not thermodynamically favorable, because K3<1
b. thermodynamically favorable, because K3>1
O2 (g) + 2H+ (aq) +2 e- -> H2O2 (ag) What is the standard reduction potential for the half-reaction represented above? a. -1.78 V b. -0.68 V c. +0.68 V d. +1.78 V
c. +0.68 V
A 6.0 mol sample of C3H8 (g) and a 20. mol sample of Cl2 (g) are placed in a previously evacuated vessel, where they react according to the equation above. After one of the reactants has been totally consumed, how many moles of HCl (g) have been produced? a. 4.0 mol b. 8.0 mol c. 20. mol d. 24 mol
c. 20. mol
Approximately how long did it take for 75 percent of the initial amount of C25H30N3+ (aq) to react? a. 75 s b. 225 s c. 300 s d. 600 s
c. 300 s
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. 500 K and 0.10 atm
To choose a wavelength to analyze the progress of the reaction, a student records the absorbance spectra of both C25H30N3+ (aq) and C25H30N3OH (aq) in the range of 200-800 nm. The two spectra are presented in the graph below. The student wants to use the spectrophotometer to measure [C25H30N3+] with the greatest sensitivity as the reaction progresses. Which of the following indicates the best wavelength setting and explains why it is best? a. 205 nm, because the colorless form of the molecule will absorb significantly at this wavelength b. 205 nm, because both forms of the molecule will absorb significantly at this wavelength c. 590 nm, because only the violet form of the molecule will absorb significantly at this wavelength d. 590 nm, because this wavelength falls in the violet region of the visible light spectrum
c. 590 nm, because only the violet form of the molecule will absorb significantly at this wavelength
Which of the following best helps to explain why the value of delta H for the dissolving CaF2 in water is positive? a. CaF2 (s) is insoluble in water b. CaF2 (s) dissolves in water to form CaF2 (aq) particles c. Ca2+ ions have very strong ion-ion interactions with F- ions in the crystal lattice d. Ca2+ ions have very strong ion-dipole interactions with water molecules in the solution
c. Ca2+ ions have very strong ion-ion interactions with F- ions in the crystal lattice
Which of the following equations represents a reaction for which of the standard entropy change is positive (delta s > 0) a. 3 O2 (g) -> 2 O3 (g) b. 2 H2 (g) + O2 (g) -> 2H2O (l) c. CaCO3 (s) -> CaO (s) + CO2 (g) d. I2 (g) + 2K (s) -> 2 KI (s)
c. CaCO3 (s) -> CaO (s) + CO2 (g)
A solution containing HCL and the weak acid HClO2 has a pH of 2.4. Enough KOH (aq) is added to the solution to increae the pH to 10.5. The amount of which of the following species increases as the KOH (aq) is added? a. Cl- (aq) b. H+ (aq) c. ClO2- (aq) d. HClO2 (aq)
c. ClO2- (aq)
A solution is prepared by adding 100 mL of 1.0 M HC2H3O2 (aq) to 100 mL of 1.0 M NaC2H3O2 (aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0 M HCl are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH? a. H3O+ (aq) + OH- (aq) -> 2 H2O (l) b. H3O+ (aq) + Cl- (aq) -> HCl (g) + H2O (l) c. H3O+ (aq) + C2H3O2- (aq) -> HC2H3O2 (aq) + H2O (l) d. H3O+ (aq) + HC2H3O2 (aq) -> H2C2H3O2+ (aq) + H2O (l)
c. H3O+ (aq) + C2H3O2- (aq) -> HC2H3O2 (aq) + H2O (l)
Which of the following explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased to 650 K? a. Kc will increase because the activation energy of the forward reaction increases b. Kc will increase because there are more reactant molecules than product molecules c. Kc will decrease because the reaction is exothermic d. Kc is constant and will not change
c. Kc will decrease because the reaction is exothermic
Atoms of which element are reduced in the reaction? a. S; each atom loses four electrons b. Na in Na2O2; each atom loses one electron c. O in Na2O2; each atom gains one electron d. O in H2O; each atom gains one electron
c. O in Na2O2; each atom gains one electron
Based on the ionization energies of element X given in the table above, which of the following is most likely the empirical formula of an oxide of element X? a. XO2 b. X2O c. X2O3 d. X2O5
c. X2O3
A 2.0 mol sample of CO (g) and a 2.0 mol sample of H2O (g) are introduced into a previously evacuated 100. L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium? a. [H2O] > [CO] and [CO2] > [H2] b. [H2O] > [H2] c. [CO2] > [CO] d. [CO] = [H2O] = [CO2] = [H2]
c. [CO2] > [CO]
A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings? a. a strong acid was titrated with a strong base, as evidenced by the equivalence point at pH=7 b. a strong acid was titrated with a strong base, as evidenced by the equivalence point at pH >7 c. a weak acid was titrated with a strong base, as evidenced by the equivalence point at pH >7 d. a weak acid was titrated with a weak base, as evidenced by the equivalence point at pH approximately 7
c. a weak acid was titrated with a strong base, as evidenced by the equivalence point at pH >7
Which of the following best describes what happens to the pH of he H2O2 solution as the titration proceeds? a. the +2 charge on the manganese ions maintains the acidity of the solution b. the production of water dilutes the solution, making it basic c. as H+ ions are consumed, the solution becomes less acidic and the pH increases d. as H+ ions are consumed, the solution becomes less acidic and the pH decreases
c. as H+ ions are consumed, the solution becomes less acidic and the pH increases
Based on the information above, which of the following is true? a. only mechanism 1 is consistent with the rate law b. only mechanism 2 is consistent with the rate law c. both mechanism 1 and mechanism 2 are consistent with the rate law d. neither mechanism 1 nor mechanism 2 is not consistent with the rate law
c. both mechanism 1 and mechanism 2 are consistent with the rate law
Which of the following is true for the decomposition of H2O2 (aq)? a. delta G >0 and Keq >1 b. delta G >0 and Keq <1 c. delta G <0 and Keq >1 d. delta G <0 and Keq <1
c. delta G <0 and Keq >1
The reaction is thermodynamically favorable under standard conditions at 298 K. Therefore, the value of delta s for the reaction must be a. equal to zero b. equal to detla H/298 K c. greater than delta H/298K d. less than delta H/298 K
c. greater than delta H/298K
The best explanation for the lower pressure in container 4 is that SO2 molecules a. have a larger average speed than the other three gases b. occupy a larger portion of the container volume than the other three gases c. have stronger inter-molecular attractions than the other three gases d. contain pi bonds, while the other gases contain only sigma bonds
c. have stronger inter-molecular attractions than the other three gases
At room temperature I2 (s) is a molecular solid. Which of the following provides a characteristic of I2 (s) with a correct explanation? a. it has a high melting point because it has weak intermolecular forces b. it is hard because it forms a three-dimensional covalent network c. it is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs d. it is very soluble in water because its molecules are polar
c. it is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs
Which of the following statements about the thermodynamic favorability of the reaction at 298 K is correct? a. it is thermodynamically unfavorable b. it is thermodynamically favorable and is driven by delta S only c. it is thermodynamically favorable and is driven by delta H only d. it is thermodynamically favorable and is driven by both delta H and delta S
c. it is thermodynamically favorable and is driven by delta H only
What can be inferred about delta S for the reaction at 600 K? a. it must be positive, since the reaction is thermodynamically unfavorable at 600 K b. it must be negative, since there are more moles of products than reactants c. it must be positive, since delta G is negative and delta H is positive d. it must be negative, since delta G is positive and delta H is positive
c. it must be positive, since delta G is negative and delta H is positive
Two trials are run, using excess water. In the first trial, 7.8g of Na2O2 (s) (molar mass 78 g/mol) is mixed with 3.2 g of S (s). In the second trial, 7.8g of Na2O2 (s) is mixed with 6.4g of S (s). The Na2O2 (s) and S (s) react as completely as possible. Both trials yield the same amount of SO2 (aq). Which of the following identifies the limiting reactant and the heat released, q, for the two trials at 298 K? a. limiting reactant: S // q: 30. kJ b. limiting reactant: S // q: 60 kJ c. limiting reactant: Na2O2 // q: 30. kJ d. limiting reactant: Na2O2 // q: 61 kJ
c. limiting reactant: Na2O2 // q: 30. kJ
A 1.0 L solution of AgNO3 (aq) and Pb(NO3)2 (aq) has a Ag+ concentration of 0.020 M and a Pb+ concentration of 0.0010 mol sample of K2SO4 (s) is added to the solution. Based on the information in the table above, which of the following will occur? (Assume that the volume change of the solution is negligible). a. No precipitate will form b. only Ag2SO4 (s) will precipitate c. only PbSO4(s) will precipitate d. both Ag2SO4(s) and PbSO4 (s) will precipitate
c. only PbSO4(s) will precipitate
The volume of a sample of air in a cylinder with a movable piston is 2.0 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 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. the average kinetic energy stays the same
For element X represented above, which of the following is most likely explanation for the large difference between the second and third ionization energies? a. the effective nuclear charge decreases with successive ionizations b. the shielding of outer electrons increases with successive ionizaitons c. the electron removed during the third ionization is, on average, much closer to the nucleus that the first two electrons removed were d. the ionic radius increases with successive ionization
c. the electron removed during the third ionization is, on average, much closer to the nucleus that the first two electrons removed were
Which of the following statements is true about bond energies in this reaction? a. the energy absorbed as the bonds in the reactants are broken is greater than the energy released as the bonds in the products are formed b. the energy released as the bonds in the reactants are broken is greater than the energy absorbed as the bonds in the product are formed c. the energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed d. the energy released as the bonds in the reactants are broken is less than the energy absorbed as the bonds int he product are formed
c. the energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed
One student titrated the NaOH (aq) with 1.0 M HCl (aq) instead of 0.10 M HCl (aq). How would the student's titration curve differ from the original curve? a. the initial pH would be 11 instead of 13 b. the pH at the equivalence point would be 5 instead of 7 c. the pH far beyond the equivalence point would be higher than in the original curve d. the pH far beyond the equivalence point would be lower than in the original curve
c. the pH far beyond the equivalence point would be higher than in the original curve
At a certain point in time, a 1.00 L rigid reaction vessel contains 1.5 mol of PCl3 (g), 1.0 mol of Cl2 (g), and 2.5 mol of PCl5 (g). Which of the following describes how the measured pressure in the reaction vessel will change and why it will change that way as the reaction system approaches equilibrium at constant temperature? a. the pressure will increase because Q<Kc b. the pressure will increase because Q>Kc c. the pressure will decrease because Q<Kc d. the pressure will decrease because Q>Kc
c. the pressure will decrease because Q<Kc
Two samples of Mg (s) of equal mass were placed in equal amounts of HCl (aq) contained in two separate reaction vessels. Particle representations of the mixing of Mg (s) and HCl (aq) in the two reaction vessels are shown in Figure 1 and Figure 2 above. Water molecules are not included in the particle representations. Which of the reactions will initially proceed faster, and why? a. the reaction in Figure 1, because the atoms of Mg are more concentrated than those in Figure 2 b. the reaction in Figure 1, because the Mg (s) in Figure 1 has a larger mass than the Mg (s) in Figure 2 c. the reaction in Figure 2, because more Mg atoms are exposed to HCl (aq) in Figure 2 than in Figure 1 d. the reaction in Figure 2, because the Mg (s) in Figure 2 has less surface area than the Mg (s) in Figure 1
c. the reaction in Figure 2, because more Mg atoms are exposed to HCl (aq) in Figure 2 than in Figure 1
What happens to the temperature of the contents of the vessel as the reaction occurs? a. the temperature must increase, because according to Le Chatelier's principle, an increase in temperature cause more products to form b. the temperature must decrease, because the reaction takes place at a temperature above room temperature c. the temperature must decrease, because the reaction is endothermic d. the temperature does not change, because the vessel is insulated
c. the temperature must decrease, because the reaction is endothermic
The table above shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionization energy of oxygen from the overall trend? a. the atomic radius of oxygen is greater than the atomic radius of fluorine b. the atomic radius of oxygen is less than the atomic radius of nitrogen c. there is repulsion between paired electrons in the oxygen's 2p orbitals d. there is attraction between paired electrons in oxygen's 2p orbitals
c. there is repulsion between paired electrons in the oxygen's 2p orbitals
Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds. Which of the following diagrams shows the correct representation of the hydrogen bonding between thymine and adenine base pairs? a. b. c. d.
d.
Fe (s) + 2HCl (aq) -> FeCl2 (aq) + H2 (g) When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powedered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true? a. HCl is in excess, and 0.100 mol of HCl remains unreacted b. HCl is in excess, and 0.020 mol of HCl remains unreacted c. 0.015 mol of FeCl2 has been produced d. 0.22 L of H2 has been produced
d. 0.22 L of H2 has been produced
A sample of CH3OH (g) is placed in the previously evacuated vessel with a pressure of P1 at 600 K. What is the final pressure in the vessel after the reaction is complete and the contents of the vessel are returned to 600 K? a. P1/9 b. P1/3 c. P1 d. 3P1
d. 3P1
At a certain time during the titration, the rate of appearance of O2 (g) was 1.0 x 10^-3 mol/(LS). What was the rate of disappearance of MnO4- at the same time? a. 6.0 x 10^-3 mol/(LS) b. 4.0 x 10^-3 mol/(LS) c. 6.0 x 10^-4 mol/(LS) d. 4.0 x 10^-4 mol/(LS)
d. 4.0 x 10^-4 mol/(LS)
Which of the following correctly identifies which has the higher first-ionization energy, Cl or Ar, and supplies the best justification? a. Cl, because of its higher electronegativity b. Cl, because of its higher electron affinity c. Ar, because of its completely filled valence shell d. Ar, because of its higher effective nuclear charge
d. Ar, because of its higher effective nuclear charge
In which of the following liquids do the intermolecular forces include dipole-dipole forces? a. F2(l( b. CH4 (l) c. CF4 (l) d. CH2F2 (l)
d. CH2F2 (l)
The photoelectron spectra of the Is electrons of two isoelectronic species, Ca2+ and Ar, are shown above. Which of the following correctly identifies the species associated with peak X and provides a valid justification? a. Ar, because it has completely filled energy levels b. Ar, because its radius is smaller than the radius of Ca2+ c. Ca2+, because its nuclear mass is greater than that of Ar d. Ca2+, because its nucleus has two more protons than the nucleus of Ar has
d. Ca2+, because its nucleus has two more protons than the nucleus of Ar has
A sealed rigid vessel contains BaO2 (s) in equilibrium with BaO (s) and O2 (s) as represented by the equation above. Which of the following changes will increase the amount of BaO2 (s) in the vessel? a. Removing a small amount of O2 (g) b. Removing a small amount of BaO (s) c. Adding He gas to the vessel d. Lowering the temperature
d. Lowering the temperature
Based on the information above and periodic trends, which of the following is the best hypothesis regarding the oxide (s) formed by Rb? a. Rb will form only Rb2O b. Rb will only form only RbO2 c. Rb will form only Rb2O and Rb2O2 d. Rb will form Rb2O, Rb2O2, and RbO2
d. Rb will form Rb2O, Rb2O2, and RbO2
Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest? a. X < Y < Z b. X < Z < Y c. Y < Z < X d. Z < Y < X
d. Z < Y < X
NH3 (g) was synthesized at 200 degrees C in the presence of a powdered Os (s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3 (g) in the mixture after equilibrium is reestablished? a. replacing the powdered Os (s) with a solid cube of Os (s) of the same total mass b. increasing the temperature of the system to 250 degrees C at constant pressure c. removing some H2 (g) d. adding some N2 (g)
d. adding some N2 (g)
The auto-ionization of water is represented by the equation above (2H2O -><- H3O+ (aq) + OH- (aq)) Values of pKw at various temperatures are listed in the table below. Based on the information above, which of the following statements is true? a. the dissociation of water is an exothermic process b. the pH of pure water is 7.00 at any temperature c. as the temperature increases, the pH of pure water increases d. as the temperature increases, the pH of pure water decreases
d. as the temperature increases, the pH of pure water decreases
Which of the following best helps explain why an increase in temperature increases the rate of a chemical reaction? a. at higher temperatures, reactions have a lower activation energy b. at higher temperatures, reactions have a higher activation energy c. at higher temperatures, every collision results in the formation of product d. at higher temperatures, high-energy collisions happen more frequently
d. at higher temperatures, high-energy collisions happen more frequently
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. the combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container
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 teh 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 he 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 abosrbance d. the cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer
d. the cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer
A student performed an analysis to determine the amount of AgNO3 (aq) in a solution. Excess NaCl (aq) was added to the solution, and the Ag+ (aq) precipitated as AgCl (s). The precipitate was collected by gravity filtration and dried in an oven. Three trials were performed, and in each case, according to the instructor, the mass of precipitate recovered was 5 percent higher than the actual mass of AgCl (s) that should have formed. Which of the following could account for the error? a. the pores in the filter paper were too large b. not all of the precipitate was transferred to the filter paper c. the NaCl (aq) solution was too concentrated d. the precipitate was not rinsed with deionized water before drying
d. the precipitate was not rinsed with deionized water before drying
Which of the following most likely accounts for the difference between reaction path one and reaction path two? a. a higher temperature in path one b. a higher temperature in path two c. the presence of a catalyst in path one d. the presence of a catalyst in path two
d. the presence of a catalyst in path two
During the course of the experiment, which of the following happens to the NO3- ions? a. they are oxidized by Cl- ions b. they are reduced to NO2- ions c. they are decomposed by reacting with M+ ions d. they remain dissolved in the filtrate solution
d. they remain dissolved in the filtrate solution
The BF3 molecule i nonpolar, whereas the NF3 molecule is polar. Which of the following statements accounts for the the difference in polarity of the two molecules? a. in NF3, each F is joined to N with multiple bonds, whereas in BF3, each F is joined to B with single bonds b. N-F bonds are polar, whereas B-F bonds are nonpolar c. NF3 is an ionic compound, whereas BF3 is a molecular compound d. unlike BF3, NF3 has a nonplanar geometry due to an unshared pair of electrons on the N atom
d. unlike BF3, NF3 has a nonplanar geometry due to an unshared pair of electrons on the N atom
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
forces among Br₂ molecules are stronger than those among Cl₂ molecules
The amount of H2 (g) present in a reaction mixture at equilibrium can be maximized by
increasing the temperature and decreasing the pressure by increasing the volume
Compared to the equilibrium vapor pressure of CH3OH at 300K, the equilibrium vapor pressure of C2H5OH at 300 K is
lower, because London dispersion forces among C2H5OH molecules are greater than those among CH3OH molecules
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?
r = k (NOBr)2