AP Chem Unit 3 MC

A gaseous air‑fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air‑fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air‑fuel mixture?

About 12atm, because the volume of the gas mixture decreased by a factor of 12.

The diagrams above represent two allotropes of solid phosphorus. Which of the following correctly identifies the allotrope with the higher melting point and explains why?

Allotrope II, because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between theP4 molecules in allotrope I.

The structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite?

Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces.

The diagram above represents four cations, all shown to the same scale. Which cation would be predicted by Coulomb's law to have the strongest ion-dipole attraction to water, and why?

Mg2+, because it has the largest charge-to-size ratio.

The crystal structure of NaBrNaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(s)NaBr(s) to molten NaBr(l)NaBr(l) in terms of electrical conductivity?

CrystallineNaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C2H6OC2H6O, molecules?

Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule.

A solid compound of a group 1 (alkali) metal and a group 17 (halogen) element dissolves in water. The diagram above represents one type of solute particle present in the solution. Which of the following identifies the solute particle and best helps explain how the solute particle interacts with water molecules?

The particle is a positive ion, and the interactions are ion-dipole attractions.