Intermolecular Forces - UNSOLVED PRACTICE SET
Chapter: States of Matter | Topic: Intermolecular Forces
INTERMOLECULAR FORCES - UNSOLVED PRACTICE SET
Topic: Intermolecular Forces
Multiple Choice Questions
Q1. Which of the following is the strongest intermolecular force?
- London dispersion forces
- Dipole-dipole interactions
- Hydrogen bonding
- Ion-dipole interactions
Q2. London dispersion forces are present in:
- Only polar molecules
- Only non-polar molecules
- All molecules, both polar and non-polar
- Only ionic compounds
Q3. Hydrogen bonding is possible in a molecule when hydrogen is bonded to:
- Any electronegative atom
- Only fluorine
- Fluorine, oxygen, or nitrogen
- Only carbon
Q4. The intermolecular force responsible for the high boiling point of water is:
- London dispersion forces
- Dipole-dipole interactions
- Hydrogen bonding
- Covalent bonding
Q5. Which of the following molecules will have the strongest London dispersion forces?
- CH₄
- C₂H₆
- C₃H₈
- C₄H₁₀
Q6. Dipole-induced dipole interactions occur between:
- Two polar molecules
- Two non-polar molecules
- A polar molecule and a non-polar molecule
- Two identical atoms
Short Answer Questions
Q7. Define intermolecular forces. How do they differ from intramolecular forces? Give one example of each.
Q8. Explain London dispersion forces. Why are they also called 'instantaneous dipole-induced dipole forces'?
Q9. Why does H₂O have a higher boiling point than H₂S, even though both are group 16 hydrides? Explain in terms of intermolecular forces.
Q10. Arrange the following in order of increasing strength of intermolecular forces: London forces, dipole-dipole interactions, hydrogen bonding, ion-dipole interactions. Give a brief reason for your arrangement.
Q11. Explain why NH₃ can form hydrogen bonds but CH₄ cannot, even though both contain hydrogen.
Q12. What are ion-dipole interactions? In which type of solutions are they most commonly observed?
Long Answer Questions
Q13. (a) Define the following types of intermolecular forces and give one example for each:
(i) London dispersion forces
(ii) Dipole-dipole interactions
(iii) Hydrogen bonding
(iv) Ion-dipole interactions
(b) Arrange the following substances in order of increasing boiling point and justify your answer:
CH₃OH, CH₃CH₂OH, CH₃OCH₃, CH₄
(c) Explain why hydrogen fluoride (HF) has a higher boiling point than hydrogen chloride (HCl), despite HCl having a higher molecular mass.
Q14. (a) Explain the origin of London dispersion forces. Why do they increase with increasing molecular size and mass?
(b) Compare the intermolecular forces present in:
(i) Solid iodine (I₂)
(ii) Liquid hydrogen chloride (HCl)
(iii) Aqueous solution of sodium chloride
(iv) Liquid ammonia (NH₃)
(c) A student claims that since noble gases are monoatomic and non-polar, they have no intermolecular forces. Is the student correct? Explain.
Q15. (a) What is hydrogen bonding? Explain the two types of hydrogen bonding (intermolecular and intramolecular) with suitable examples.
(b) Explain the following observations using hydrogen bonding:
(i) Ice is less dense than water
(ii) Ethanol is miscible with water but ethane is not
(iii) o-nitrophenol has a lower boiling point than p-nitrophenol
(c) In the Indian context, explain why cotton clothes are preferred in summer. How do hydrogen bonds in cellulose fibres contribute to the comfort of cotton clothing?
Numerical / Application-Based Problems
Q16. The boiling points of some group 16 hydrides are given below:
H₂O: 100°C
H₂S: –60°C
H₂Se: –41°C
H₂Te: –2°C
(a) Explain why H₂O has an anomalously high boiling point compared to other hydrides in the group.
(b) Predict the trend in boiling points from H₂S to H₂Te and explain your reasoning based on intermolecular forces.
(c) Calculate the difference in boiling points between H₂O and H₂S. How much of this difference can be attributed to hydrogen bonding?
(d) Draw a diagram showing how two water molecules are held together by hydrogen bonding.
Q17. Consider the following substances and their properties:
| Substance | Molecular Mass (g/mol) | Boiling Point (°C) |
|---|---|---|
| CH₄ | 16 | –161 |
| NH₃ | 17 | –33 |
| H₂O | 18 | 100 |
| Ne | 20 | –246 |
(a) Explain why NH₃ and H₂O have much higher boiling points than CH₄ and Ne, despite having similar molecular masses.
(b) Calculate the ratio of boiling points (in Kelvin) of H₂O to CH₄. What does this ratio tell you about the relative strength of intermolecular forces?
(c) Neon has a higher molecular mass than CH₄ but a lower boiling point. Explain this observation.
(d) A student predicts that HF should have a higher boiling point than H₂O because fluorine is more electronegative than oxygen. Is this prediction correct? Explain with actual data (bp of HF = 19.5°C).
Q18. In daily life in India, intermolecular forces play crucial roles:
(a) During the monsoon season, clothes take longer to dry. Explain this in terms of intermolecular forces between water molecules and fabric fibres.
(b) Why does a wet khus (vetiver) curtain cool the room when air passes through it? Explain using the concept of hydrogen bonding and evaporation.
(c) Honey is more viscous than water. Explain how the extensive hydrogen bonding network in honey contributes to its high viscosity.
(d) A student notices that naphthalene balls (used to protect clothes from moths) gradually disappear over time without leaving any liquid. Explain this phenomenon (sublimation) in terms of the intermolecular forces present in naphthalene crystals.