AP Chemistry Practice Quiz: Intermolecular and Interparticle Forces

Correct Answer: C

According to the provided content, hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (N, O, or F) and is attracted to another N, O, or F atom in a nearby molecule. In CH₃OH, a hydrogen atom is directly bonded to an oxygen atom, allowing it to form hydrogen bonds.

Correct Answer: C

Both Br₂ and Cl₂ are nonpolar molecules, so their primary intermolecular force is the London dispersion force (LDF). The content states that LDFs increase with polarizability, which in turn increases with the electron count. Since a bromine atom has more electrons than a chlorine atom, the Br₂ molecule has stronger LDFs, requiring more energy to overcome and thus resulting in a higher boiling point.

Correct Answer: C

The provided text explicitly states that ion-dipole forces, which exist between ions and polar molecules, are 'typically stronger than dipole-dipole forces.' They are also stronger than the other listed forces because they involve the interaction between a full ionic charge and a partial charge (dipole), which is a stronger electrostatic attraction.

Correct Answer: B

The content states that London dispersion forces (LDFs) 'increase with contact area and polarizability (which increases with electron count)' and 'are often the strongest IMF in large molecules.' Even though wax is nonpolar, its large size gives it significant LDFs that, in aggregate, are stronger than the dipole-dipole forces in the small HCl molecule.

Correct Answer: D

When an ionic solid like KCl dissolves in a polar solvent like water, the K⁺ and Cl⁻ ions are separated and surrounded by water molecules. The force of attraction between an ion (K⁺ or Cl⁻) and a polar molecule (H₂O) is defined as an ion-dipole force.

Correct Answer: B

The content states that 'Noncovalent interactions (IMFs) are crucial in large biomolecules and polymers, where they dictate the molecular shape and functionality.' This includes a combination of forces like hydrogen bonds, dipole-dipole interactions, and London dispersion forces that collectively hold the polymer chain in its specific functional conformation.

Correct Answer: C

The content specifies that polarizability increases with electron count, molecular size, and pi bonding. Polarizability is the measure of how easily an electron cloud can be distorted to create a temporary dipole. A permanent dipole moment is a fixed separation of charge in a polar molecule and is distinct from the ability to have a dipole induced.

Correct Answer: B

The content explains that dipole-dipole forces are understood by 'considering the interaction of partial charges.' For an attractive force, the partially positive end of one dipole (the H in HBr) will be attracted to the partially negative end of another dipole (the Br in another HBr molecule), following the basic electrostatic principle that opposite charges attract.

Correct Answer: D

Dipole-induced dipole interactions occur between a polar molecule and a nonpolar molecule. In the options, HCl is a polar molecule (it has a permanent dipole moment), and Ar is a nonpolar species. The permanent dipole of HCl induces a temporary dipole in the electron cloud of the Ar atom, leading to a weak attraction.

Correct Answer: C

Both molecules are nonpolar isomers, so they have the same molar mass and electron count. The key difference is their shape. The linear n-butane molecule has a larger surface area, allowing for more points of contact with neighboring molecules. The content states that LDFs increase with contact area, so n-butane experiences stronger LDFs and has a higher boiling point than the more compact, spherical isobutane.

Correct Answer: D

The provided text explicitly defines hydrogen bonding as 'a strong dipole-dipole interaction.' It occurs in molecules where H is bonded to N, O, or F, which creates a very large partial positive charge on the hydrogen and a large partial negative charge on the N, O, or F, leading to an exceptionally strong attraction between molecules.

Correct Answer: B

This question requires comparing the dominant IMF in each species. CH₄ is nonpolar (LDFs only). NH₃ is polar and can hydrogen bond. H₂O is also polar and can hydrogen bond. Both NH₃ and H₂O have stronger IMFs than CH₄. Between H₂O and NH₃, oxygen is more electronegative than nitrogen, making the O-H bond more polar than the N-H bond. This results in stronger hydrogen bonds for H₂O. Therefore, the order of increasing IMF strength is CH₄ (LDF) < NH₃ (H-bond) < H₂O (stronger H-bond).