AP Chemistry Unit 3.1

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C₂H₆O, molecules?

• Diagram 1, because it shows hydrogen bonds forming between hydrogen atoms from different ethanol molecules.

• Diagram 1, because it shows strong, directional dipole-dipole forces between two polar ethanol 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.

• Diagram 2, because it shows the dipole from an ethanol molecule inducing a dipole in another ethanol molecule.

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?

• Li⁺, because it is the smallest group 1 metal ion.

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

• Na⁺, because it has the smallest charge-to-size ratio.

• Ca²⁺, because it is the largest group 2 metal ion.

Tags

NGSS.HS-PS2-4

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 negative ion, and the interactions are hydrogen bonds.

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

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

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

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 I, because it has P₄ molecules with covalent bonds that are stronger than dispersion forces between individual P atoms in allotrope II.

• Allotrope II, because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P₄ molecules in allotrope I.

• Allotrope II, because it has metallic bonding that is stronger than the covalent bonding found in the P₄ molecules in allotrope I.

• Both allotropes have the same melting point because they both contain phosphorous atoms.

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

• Crystalline NaBr contains no freely moving electrons that could conduct an electrical current, whereas electrons can flow freely in molten NaBr, which is a good conductor of electricity.

• Crystalline NaBr and molten NaBr both contain ions that are held in fixed positions due to strong electrostatic attractions among the ions, making neither a good electrical conductor.

• Crystalline NaBr and molten NaBr both contain Na atoms that transfer electrons to Br atoms in a chemical reaction, thus allowing them both to be good conductors of electricity.

• Crystalline NaBr 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.

Tags

NGSS.HS-PS2-5

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?

• Diamond contains covalent bonds, whereas graphite contains ionic bonds.

• Diamond contains ionic bonds, whereas graphite contains covalent bonds.

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

• Carbon atoms in diamond have a sea of mobile electrons that make the structure strong, whereas graphite does not contain delocalized electrons.