Pre AP Chemistry -2.1D Intermolecular and Intramolecular Forces- MCQ Exam Style Questions -New Syllabus 2025-2026
Pre AP Chemistry -2.1D Intermolecular and Intramolecular Forces- MCQ Exam Style Questions – New Syllabus 2025-2026
Pre AP Chemistry -2.1D Intermolecular and Intramolecular Forces- MCQ Exam Style Questions – Pre AP Chemistry – per latest Pre AP Chemistry Syllabus.
Which type of intermolecular force is present in all molecules, regardless of polarity?
(A) Hydrogen bonding
(B) Dipole–dipole interactions
(C) London dispersion forces
(D) Ion–dipole interactions
▶️ Answer / Explanation
London dispersion forces arise from temporary dipoles caused by movement of electrons.
Since all atoms and molecules contain electrons, London dispersion forces are present in every substance.
Answer: C
Which pair of molecules can form hydrogen bonds with each other?
(A) \(CH_4\) and \(NH_3\)
(B) \(HF\) and \(H_2O\)
(C) \(CCl_4\) and \(HCl\)
(D) \(N_2\) and \(O_2\)
▶️ Answer / Explanation
Hydrogen bonding occurs when hydrogen is bonded to F, O, or N.
Both \(HF\) and \(H_2O\) contain these bonds and can form hydrogen bonds with each other.
Answer: B
The boiling points of noble gases increase from He to Xe. What explains this trend?
(A) Increasing electronegativity
(B) Stronger nuclear attraction
(C) Increasing polarizability causing stronger London dispersion forces
(D) Formation of hydrogen bonds
▶️ Answer / Explanation
Larger atoms have more electrons and more easily distorted electron clouds.
This increases polarizability, strengthening London dispersion forces and increasing boiling point.
Answer: C
A covalent bond between atoms in a molecule is broken during a reaction. A student claims this is an intermolecular force being overcome. Is the student correct?
(A) Yes — covalent bonds are intermolecular forces
(B) No — covalent bonds are intramolecular forces
(C) No — only ionic bonds are intramolecular
(D) Yes — all atomic forces are intermolecular
▶️ Answer / Explanation
Covalent bonds hold atoms together within a molecule, so they are intramolecular forces.
Intermolecular forces act between separate molecules.
Answer: B
The table shows boiling points of three compounds.
| Compound | Molar Mass | Boiling Point |
|---|---|---|
| \(CH_3CH_2CH_3\) | 44 | -42°C |
| \(CH_3OCH_3\) | 46 | -24°C |
| \(CH_3CH_2OH\) | 46 | 78°C |
Why does ethanol have a much higher boiling point?
(A) Higher molar mass
(B) Hydrogen bonding in ethanol
(C) Fewer electrons in dimethyl ether
(D) Ethanol is ionic
▶️ Answer / Explanation
Ethanol contains an O–H bond, allowing molecules to form hydrogen bonds.
Dimethyl ether cannot form hydrogen bonds between its molecules.
Hydrogen bonding significantly increases boiling point.
Answer: B
Which sequence correctly ranks the following substances in order of increasing boiling point?
(A) \(Ne < HF < HCl < NaCl\)
(B) \(Ne < HCl < HF < NaCl\)
(C) \(HCl < Ne < HF < NaCl\)
(D) \(Ne < HCl < NaCl < HF\)
▶️ Answer / Explanation
Strength of attractive forces:
Ne → London dispersion only (very weak)
HCl → dipole–dipole + LDF
HF → strong hydrogen bonding
NaCl → ionic lattice
Increasing boiling point:
\(Ne < HCl < HF < NaCl\)
Answer: B
Water has a boiling point of 100°C, whereas \(H_2S\) boils at −60°C. If hydrogen bonding did not occur in water, what would its boiling point likely be?
(A) Approximately 100°C
(B) Approximately −80°C
(C) Approximately 50°C
(D) It would increase
▶️ Answer / Explanation
Group 16 hydrides follow the trend:
\(H_2S < H_2Se < H_2Te\)
Water deviates because of strong hydrogen bonding.
Without hydrogen bonding, its boiling point would follow the normal trend and be much lower, near −80°C.
Answer: B
Pentane (\(C_5H_{12}\)) boils at 36°C while 1-butanol (\(C_4H_9OH\)) boils at 118°C. What interaction explains this difference?
(A) Hydrogen bonding between pentane molecules
(B) Hydrogen bonding between butanol molecules
(C) Ionic bonding in butanol
(D) Strong dipole-dipole forces in pentane
▶️ Answer / Explanation
1-butanol contains an O–H group allowing hydrogen bonding between molecules.
Pentane is non-polar and experiences only London dispersion forces.
Hydrogen bonding is much stronger, resulting in a higher boiling point.
Answer: B
The isomers n-pentane, isopentane, and neopentane have boiling points 36°C, 28°C, and 9.5°C respectively. What explains this trend?
(A) Increasing polarity with branching
(B) Greater branching reduces surface area and weakens London dispersion forces
(C) More hydrogen bonding in branched molecules
(D) Straight chains have fewer electrons
▶️ Answer / Explanation
Branching makes molecules more compact and spherical.
This reduces surface contact between molecules and weakens London dispersion forces.
Weaker intermolecular forces lower the boiling point.
Answer: B
When \(NaCl\) dissolves in water, which forces are overcome and which new forces form?
(A) Covalent bonds broken; hydrogen bonds formed
(B) Ionic lattice and water hydrogen bonds broken; ion–dipole interactions formed
(C) London forces broken; dipole-dipole formed
(D) Ion-dipole forces broken; ionic bonds formed
▶️ Answer / Explanation
During dissolution:
• Ionic bonds in the NaCl lattice must be overcome.
• Some hydrogen bonds between water molecules break.
New ion–dipole interactions form between water molecules and ions.
Answer: B