Sublimation of naphthalene

 

Abstract

This experiment investigates the sublimation process of naphthalene, a white crystalline solid commonly used in mothballs and as a solvent in the industry. Sublimation refers to the direct transition of a substance from solid to gas phase without passing through the liquid phase. Understanding the sublimation properties of naphthalene is important for its various applications.

Introduction

Naphthalene, with the chemical formula C₁₀H₈, exhibits sublimation at relatively low temperatures and atmospheric pressure. Sublimation is utilized in various processes, including purification techniques and the production of certain chemicals. This experiment aims to demonstrate the sublimation process of naphthalene and study its characteristics.

Details of the Experiment

Procedure

1. Place a small amount of naphthalene in a watch glass.
2. Heat the watch glass gently using a Bunsen burner.
3. Observe the naphthalene crystals disappearing and forming a vapor.
4. Place a cold surface, such as another watch glass or a Petri dish, above the vapor to observe the re-sublimation.

Observations and Calculations

Record the temperature at which naphthalene starts to sublime and the temperature at which re-sublimation occurs. Measure the amount of naphthalene remaining in the watch glass after the experiment.

Conclusion

The experiment demonstrates the sublimation process of naphthalene and its characteristic properties. The collected data can be used to determine the sublimation temperature and efficiency of naphthalene.

Precautions

• Handle naphthalene with care as it can be harmful if ingested or inhaled.
• Ensure proper ventilation in the laboratory to avoid inhaling naphthalene vapors.
• Use safety goggles and gloves to protect against potential hazards.

Short Questions with Answers

1. Define sublimation.
   Answer: Sublimation is the process where a substance transitions directly from the solid phase to the gas phase without passing through the liquid phase.
2. What is the chemical formula of naphthalene?
   Answer: The chemical formula of naphthalene is C₁₀H₈.
3. Why is naphthalene commonly used in mothballs?
   Answer: Naphthalene sublimes readily, releasing vapors that repel insects, making it effective as a moth repellent.
4. What is the appearance of naphthalene crystals?
   Answer: Naphthalene crystals are white and translucent.
5. What safety precautions should be taken when handling naphthalene?
   Answer: Safety goggles and gloves should be worn, and adequate ventilation should be ensured to avoid inhalation of vapors.
6. What is the purpose of heating the naphthalene in a watch glass?
   Answer: Heating promotes sublimation, causing naphthalene to transition from solid to vapor phase.
7. How can the sublimation temperature of naphthalene be determined?
   Answer: By observing the temperature at which naphthalene starts to sublime using a thermometer.
8. What is re-sublimation?
   Answer: Re-sublimation is the process where the vapor of a substance condenses back into solid form upon contact with a cold surface.
9. What is the significance of studying the sublimation properties of naphthalene?
   Answer: Understanding the sublimation properties helps in its applications, such as in mothballs and chemical processes.
10. Why is it important to record observations during the experiment?
    Answer: To accurately document the behavior and characteristics of naphthalene during sublimation.
11. How does the sublimation process of naphthalene contribute to its effectiveness as a moth repellent?
    Answer: The sublimation of naphthalene releases vapors that repel insects, making it an effective moth repellent.
12. What is the role of the cold surface in the experiment?
    Answer: The cold surface is used to observe re-sublimation, where the vapor of naphthalene condenses back into solid form.
13. Can naphthalene undergo reverse sublimation?
    Answer: Yes, naphthalene can undergo reverse sublimation, where the vapor condenses back into solid form upon cooling.
14. What factors can affect the rate of sublimation?
    Answer: Factors such as temperature, pressure, and surface area can affect the rate of sublimation.
15. What precautions should be taken to prevent inhalation of naphthalene vapors?
    Answer: Ensure proper ventilation and avoid prolonged exposure to naphthalene vapors.
16. How does the appearance of naphthalene crystals change during sublimation?
    Answer: Naphthalene crystals disappear as they sublime, leaving behind a residue.
17. What is the chemical nature of naphthalene?
    Answer: Naphthalene is an aromatic hydrocarbon.
18. What is the purpose of the Bunsen burner in the experiment?
    Answer: The Bunsen burner provides heat necessary for the sublimation of naphthalene.
19. How can the efficiency of naphthalene sublimation be evaluated?
    Answer: By measuring the amount of naphthalene remaining in the watch glass after the experiment.
20. What is the primary application of naphthalene besides mothballs?
    Answer: Naphthalene is used as a solvent in the industry.

Multiple Choice Questions (MCQs) with Answers

1. What is sublimation?
   • a) Transition from gas to solid phase
   • b) Transition from liquid to gas phase
   • c) Transition from solid to gas phase
   • d) Transition from liquid to solid phase
   • Answer: c) Transition from solid to gas phase
2. Which of the following best describes the appearance of naphthalene crystals?
   • a) Yellow and opaque
   • b) White and translucent
   • c) Green and transparent
   • d) Reddish-brown and opaque
   • Answer: b) White and translucent
3. What is the primary application of naphthalene besides its use in mothballs?
   • a) Food coloring
   • b) Solvent in the industry
   • c) Fertilizer additive
   • d) Flavoring agent in beverages
   • Answer: b) Solvent in the industry
4. What is the role of the Bunsen burner in the sublimation experiment?
   • a) To provide heat necessary for sublimation
   • b) To cool down the naphthalene crystals
   • c) To dissolve the naphthalene crystals
   • d) To measure the temperature of the naphthalene
   • Answer: a) To provide heat necessary for sublimation
5. What precaution should be taken to prevent inhalation of naphthalene vapors during the experiment?
   • a) Wear safety goggles
   • b) Use a Bunsen burner
   • c) Ensure proper ventilation
   • d) Handle naphthalene with bare hands
   • Answer: c) Ensure proper ventilation