AP Chemistry Semester 1 Exam Questions

In a titration experiment based on the equation above, 25.0 milliliters of an acidified Fe2+ solution requires 14.0 milliliters of standard 0.050-molar MnO4- solution to reach the equivalence point. The concentration of Fe2+ in the original solution is

E. 0.14 M

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

A. SO3

Which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (Assume all gases behave ideally.)

A. The piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules.

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

A. forces among Br2 molecules are stronger than those among Cl2 molecules

a mixture of H2 and O2 is placed in a container as represented above. the H2 and O2 react to form H2O. which of the following best represents the container after the reaction has gone to completion?

B. 2 O2 molecules and 4 H2O molecules

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. 3 CO2 molecules and 1 O2 molecules

The first five ionization energies of an unknown element are listed in the table above. Which of the following statements correctly identifies the element and cites the evidence supporting the identification?

B. Al because of the large difference between the third and fourth ionization energies

the photoelectron spectra for H and He are represented above. which of the following statements best accounts for the fact that the peak on the He spectrum is farther to the left and higher than the peak on the H spectrum?

B. He has a greater nuclear charge than H and an additional electron in the same energy level

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?

B. Sample B

Which of the following can be inferred from the diagram above that shows the dependence of potential energy on the internuclear distance between two atoms?

B. The atoms form a bond with a bond length of 75 pm

After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference?

B. The dehydrated sample absorbed moisture after heating

The diagram above represents a particle in aqueous solution. Which of the following statements about the particle is correct?

B. The particle must be an anion because the positive end of each water molecule is pointed toward it.

Which of the following happens to H atoms in the forward reaction?

C. H atoms are both oxidized and reduced.

A 20. mL sample of 0.50 M HC2H3O2(aq) is titrated with 0.50 M NaOH(aq). Which of the following best represents the species that react and the species produced in the reaction?

C. HC2H3O2(aq) + OH- ---> H2O (l) + C2H3O2- (aq)

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water?

C. NH3

The mass of the Cu(s) produced in step 3 was slightly more than the mass predicted from the 3.8 g of Cu3 (PO4)2(s) recovered from step 1. Which of the following could account for the discrepancy in the yield of Cu(s) from step 3?

C. Some unreacted Zn (s) was mixed in with the Cu(s)

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

C. 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

Another sample of eggshell reacts completely with 4.0 mL of an HCl(aq) solution of unknown concentration. If the reaction produced 0.095 atm of gas, the concentration of the HCl(aq) solution was at least

D. 1.0 M

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?

D. 3H on N connected with 3F on B

Based on the structures shown above, which of the following statements identifies the compound with the higher boiling point and provides the best explanation for the higher boiling point?

D. Compound 2, because it forms hydrogen bonds, whereas compound 1 does not.

The ideal gas law best describes the properties of which of the following gases at 0°C and 1 atm?

D. N2

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?

D. Network covalent, Metallic, Ionic

Based on the structural formulas, which of the following identifies the compound that is more soluble in water and best helps to explain why?

D. Propanol, because its molecules can form hydrogen bonds with water molecules but those of ethane cannot.

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?

D. 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 25°C?

D. The London dispersion forces are stronger in CI4 than in CCl4 because CI4 has a more polarizable electron cloud than CCl4

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?

D. The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does.

A sample of at is mixed with a sample of at . Which of the following correctly predicts the changes in average kinetic energy and the average speed of the atoms that will occur as the mixture approaches thermal equilibrium?

D. decrease decrease

Which of the following best helps to explain why Na(s) is more reactive with water than Mg(s) is?

D. the first ionization energy of Na is less than that of Mg

Which of the following best describes the change that takes place immediately after the CH3OH(l) is introduced into the previously evacuated vessel?

D: a physical change takes place because intermolecular attractions are overcome

Of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why?

B. 0.1 M KI (aq) because KI completely dissociates in water to produce ions.

Which of the following Lewis electron-dot diagrams represents the molecule that is the most polar?

A. ClF

Which of the following has the bonds arranged in order of decreasing polarity?

A. H−F > N−F > F−F

If 3.8 g of Cu3 (PO4)2(s) was recovered from step 1, what was the approximate [Cu2+] in the original solution? (The molar mass of Cu3 (PO4)2 is 381 g/mol.)

B. 0.3M

When 70. g of Li3N(s) (molar mass 35 g/mol) reacts with excess H2 (g), 8.0 g of LiH(s) is produced. The percent yield is closest to

B. 25%

In the reaction represented above, what is the hybridization of the C atoms before and after the reaction occurs?

D. Before=sp² After= sp³

2 H2O2(l) → 2 H2O(l) + O2(g) The exothermic process represented above is best classified as a

D. chemical change because covalent bonds are broken and new covalent bonds are formed

Which compound, chloroacetic acid or iodoacetic acid, most likely has the lower boiling point, and why?

A. Chloroacetic acid, because the London dispersion forces among its molecules are weaker.

The Maxwell-Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. Which gas has the greater molar mass?

A. Gas A

Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?

B. HF, because its molecules form hydrogen bonds

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?

B. Zr

Solid carbon tetrachloride, CCl4 , is represented by the diagram above. The attractions between the CCL4 molecules that hold the molecules together in the solid state are best identified as

B. nonpolar covalent bonds

When 4.0 L of He(g), 6.0 L of N2 (g), and 10. L of Ar(g), all at 0°C and 1.0 atm, are pumped into an evacuated 8.0 L rigid container, the final pressure in the container at 0°C is

C. 2.5 atm

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.)

C. 4 x 10⁻⁶

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. 5H2O2 and 2Mn

a student titrates 10.0mL samples of 1.0 M solutions of each of the haloacetic acids with a standard solution of NaOH. which of the following statements correctly predicted the volume of needed to reach the equivalence point

C. All of the acids will need the same volume of NaOH(aq) to reach the equivalence point.

The compound CCl4 is nonflammable and was once commonly used in fire extinguishers. On the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistant chemical?

C. CBr4