AP CHEM practice
O2(g)+2H+(aq)+2e- ->H2O2(aq) What is the standard reduction potential for the half reaction represented above?
+0.68 V
A student mixes a 10.0 mL sample of 1.0 M NaOH(aq) with a 10.0mL sample of 1.0M HCl(aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0°C. If the final temperature of the mixture is 26.0°C, what is the experimental value of ΔHrxn°?
-50. KJ/molrxn
Fe(s)+2HCl(aq)-> FeCl2(aq)+H2(g) When a student adds 30.0mL of 1.0 M HCl to 0.56g of powdered Fe, a reaction occurs according to the equation above. When the reaction is completed at 273 K and 1.0 atm, which of the following is true?
0.22 L of H2 has been produced.
Approximately how long did it take for 75% of the initial amount of C25H30N3+(aq) to react?
300 s
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?
3P1
...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 explain why it is best?
590 nm, because only the violet form of the molecule will absorb significantly at this wavelength.
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 weak acid was titrated with a strong base, as evidenced by the equivalence point at PH>7.
C2H4(g) +H2(g)-> C2H6(g) Which of the following will most likely increase the rate of the reaction represented above?
Adding a heterogeneous catalyst to the reaction system
N2(g)+3H2(g)->2NH3(g) ΔH<0 NH3 was synthesized at 200° 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?
Adding some N2(g)
Which of the following best help explain why an increase in temperature increases the rate of a chemical reaction?
At higher temperatures, high energy collisions happen more frequently.
A 23.0 g sample of a compound contains 12.0g of C, 3.0g of H, and 8.0g of O. Which of the following is the emperical formula of the compound?
C2H6O
In which of the following liquids do the intermolecular forces include dipole-dipole forces?
CH2F2
On the basis of the information above, which of the following arranges the binary compound in order of increasing bond polarity
CH4 <SiCl4 <SF4
Based on the information in the table above, which liquid, CS2(l) or CCl4(l), has the higher equilibrium vapor pressure at 25° C and why?
CS2(l), because it has weaker LDF
The photoelectron spectra of the 1s 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
Ca2+, because its nucleus has two more protons than the nucleus of Ar has
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?
Dotted line steep hill at beginning
A mixture containing equal number 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 explain why that occurs?
Ethyl acetate, because it has a shorter carbon chain and weaker LDF
Which of the following arranges the molecules N2, O2, and F2 in the order of their bond enthalpies, from least to greatest?
F2 <O2 <N2
2H2S(g)+CH4(g)-> CS2(g)+4H2(g) Kc=3.4x10^-4 A 0.1 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 high concentration when the system reaches equilibrium?
H2S(g)
HX(aq) +Y-(aq) ->HY(aq)+X Keq>1 Based on the information given above, which of the following is the strongest acid?
HX (aq)
At room temperature I2(g) is a molecular solid. Which of the following provides a characteristics of I2(s) with a correct explanation?
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?
It is thermodynamically favorable and is driven by ΔH° only.
What can be inferred about ΔS° for the reaction at 600 K?
It must be positive, since ΔG° is negative and ΔH° is positive.
What would be the effect on the reaction rate if the solution of C25H30N3+(aq) is diluted by a factor of two?
It would be lower
Which of the following lewis electron dot diagrams represents the molecule that contains the smallest bond angle?
NF3
2NO2(g) +F2(g) ->2NO2F(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?
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 are most likely to have the weakest interaction with an adjacent water molecule in an aqueous solution?
Na+
At the point labeled R on the pH curve, which of the following ions are presented in the reaction mixture at a concentration greater than .01M?
Na+ and Cl- only
Two trials are run, using excess water. In the first trial, 7.8g of Na2O2 (s) (molar mass 78g/mol) is mixed with 3.2 g of S(s). In the second trial, 7.8 g 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?
Na2O2 30. KJ
Atoms of which element are reduced in the reaction?
O in NaO2; each atom gains one electron
A 1.0 L solution of AgNO3(aq) and Pb(NO3)2(aq) has a Ag+ concentration of .02M and a Pb2+ concentration of .001 M. A .001 mol sample of K2SO4(s) is added to the solution. Based on the information in the table above, which of the following will occur?
Only PbSO4(s) will precipitate
Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl-]?
PbCl2
Based on the information above and periodic trends, which of the following is the best hypothesis regarding the oxide(s) formed by Rb?
Rb will form Rb2O, Rb2O2, and RbO2.
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 ideal gas law?
The combined volume of the Ar atoms are too large to be negligible compared with the total volume of the container.
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 electrons removed were.
One student titrated the NaOH(aq) with 1.0 M HCl(aq) instead of .1M HCl(aq). How would the student's titration curve differ from the original curve?
The pH far beyond the equivalence point would be lower than in the original curve.
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... Which of the following could account for the error?
The precipitate was not rinsed with deionized water before drying.
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 mixing of Mg(s) and HCl(aq) in the two reaction vessels are shown in Figure 1 and 2 above. Water molecules are not included in the particle representations. Which of the reactions will initially proceed faster and why?
The reaction in Figure 2, because more Mg atoms are exposed to HCl(aq) in Figure 2 than in Figure 1.
Which of the following statements about bonds in the reactants and products is most accurate?
The sum of the bond enthalpies of the bonds in the reactants is greater than the sum of the bond enthalpies of the bond in the products.
What happens to the temperature of the contents of the vessel as the reaction occurs?
The temperature must decrease, because the reaction is endothermic.
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?
X2O3
A student conducted an experiment to determine ΔHrxn° 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?
Y=X, because the number of moles of acid and base reacting with each other is the same in both trials.
Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest?
Z<Y<X
CO(g)+H20(g)->CO2(g)+H2(g) Kc=1.5x10^3 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?
[CO2]>[CO]
The pH of a .01M HNO2(aq) solution is in which of the following ranges? (For HNO2(aq), Ka=4x10^-4
between 2 and 3
A Sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance?
ionic bonds
Which of the following molecules is least soluble in water
the CCl4 lewis structure
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? H2(g) + Cl2(g)->2HCl(g)
the diagram that goes down 190
Which of the following is true for the decomposition of H2O2(aq)?
ΔG° <0 and Keq>1
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 of the changes in enthalpy and entropy for the process corresponding to segment X, going left to right?
ΔH°=Positive ΔS°=Positive