AP Chemistry: 3.1 Intermolecular Forces – Exam Style questions with Answer- MCQ

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Question

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, \(C_2H_6O\), molecules?

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

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

C 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.

D Diagram 2, because it shows the dipole from an ethanol molecule inducing a dipole in another ethanol molecule.
▶️Answer/Explanation

Ans:C

 Hydrogen bonding is the strongest attractive force between ethanol molecules. It requires an H atom to be bonded to a small atom with a high electronegativity, like N, O, or F. The hydrogen bond forms between atoms with partial positive and partial negative charges. In the O−H bond, the H atom has a partial positive charge, and the O atom has a partial negative charge. The hydrogen bond is formed between O−H—O−H bonds from different molecules, as shown.

Question

 

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?

A \(Li^+\) , because it is the smallest group 1 metal ion.

B \(Mg^{2+}\) , because it has the largest charge-to-size ratio.

C \(Na^+\) , because it has the smallest charge-to-size ratio.

D  \(Ca^{2+}\) , because it is the largest group 2 metal ion.

▶️Answer/Explanation

Ans:B

 Because water is polar, the O atom has a partial negative charge that can interact with cations through coulombic forces. Coulomb’s law predicts that the attractive force between the partial negative charge in the O atom and the cation will be directly proportional to the charge of the ion and inversely proportional to the size or ionic radius. Mg2+ is a relatively small ion and has the most positive charge among the cations shown.

Question

 

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?

A The particle is a negative ion, and the interactions are hydrogen bonds.
B  The particle is a negative ion, and the interactions are ion-dipole attractions.
C  The particle is a positive ion, and the interactions are ion-dipole attractions.
D  The particle is a positive ion, and the interactions are dipole-dipole attractions.
▶️Answer/Explanation

Ans: C

 The water molecules are all oriented the same way with respect to the solute particle, with the negative ends of the water molecule dipoles directed toward the solute particle. This can only be the case if the solute particle has a positive charge. The major attractive forces between the polar water molecules and the positive ion are characterized as ion-dipole attractions.

Question

 In which of the following liquids do the intermolecular forces include dipole-dipole
forces?
(A)  \(F_{2}\)(l)
(B) \(CH_{4}\)(l)
(C) \( CF_{4}\)(l)
(D) \( CH_{2}\) \(F_{2}\)

▶️Answer/Explanation

Ans:D

Question

Based on the information in the table above, which liquid, \(CS_{2}\)(l) or \(CCl_{4}\)(l), has the higher equilibrium vapor pressure at 25° C, and why?
(A) \( CS_{2}\)(l), because it has stronger London dispersion forces
(B) \(CS_{2}\)(l), because it has weaker London dispersion forces
(C) \( CCl_{4}\)(l), because it has stronger London dispersion forces
(D)  \(CCl_{4}\)(l), because it has weaker London dispersion forces

▶️Answer/Explanation

Ans:B

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