Demonstrate sublimation using solid Ammonium Chloride

Abstract

This experiment demonstrates the sublimation process using Ammonium Chloride. Sublimation is the transition of a substance directly from the solid to the gas phase without passing through an intermediate liquid phase. This experiment visually shows how Ammonium Chloride, when heated, changes directly from solid to gas.

Introduction

Sublimation is a fascinating physical change in chemistry where a solid turns directly into a gas without passing through the liquid state. Ammonium Chloride (NH4Cl) is a classic example of a sublimable solid. This experiment is important for understanding the physical properties of substances and their phase transitions under various temperature conditions. The objective is to observe and understand the conditions under which Ammonium Chloride sublimates and to apply basic principles of physical chemistry to explain the observations.

Details of the Experiment

Materials Required:

• Ammonium Chloride
• Test tube
• Bunsen burner
• Clamp stand
• Watch glass

Procedure

1. Set up the clamp stand and securely attach the test tube.
2. Place a small amount of Ammonium Chloride in the test tube.
3. Cover the top of the test tube with a watch glass.
4. Gently heat the bottom of the test tube with a Bunsen burner.
5. Observe the changes occurring to the Ammonium Chloride as it heats.
6. Notice the deposition of solid Ammonium Chloride on the cooler parts of the test tube and under the watch glass.

Observations and Calculations

As the Ammonium Chloride is heated, it sublimates from a solid directly into a gaseous state and re-deposits as a solid on the cooler parts of the test tube and the watch glass. This direct transition from solid to gas and back to solid can be observed visually.

No numerical calculations are required in this experiment as it is qualitative in nature.

Conclusion

The experiment successfully demonstrates the sublimation of Ammonium Chloride. This observation confirms that not all solids melt before vaporizing; some, like Ammonium Chloride, directly transition into the gas phase when heated, bypassing the liquid phase.

Precautions

• Handle the Bunsen burner and hot glassware with care to avoid burns.
• Ensure proper ventilation in the lab to avoid inhalation of gases.
• Wear safety goggles and gloves throughout the experiment.

Short Questions with Answers

1. What is sublimation?
   Answer: Sublimation is the process where a solid turns directly into a gas without passing through the liquid phase.
2. What substance is used to demonstrate sublimation in this experiment?
   Answer: Ammonium Chloride (NH4Cl) is used to demonstrate sublimation.
3. At what part of the test tube does the sublimation occur?
   Answer: Sublimation occurs at the bottom of the test tube where the substance is heated.
4. Where does the re-deposition of the sublimated gas occur?
   Answer: The re-deposition occurs on the cooler parts of the test tube and the watch glass.
5. What is the purpose of the watch glass in the experiment?
   Answer: The watch glass is used to observe the deposition of the sublimated solid and to prevent escape of the sublimated gas.
6. Why is Ammonium Chloride suitable for demonstrating sublimation?
   Answer: Because it readily sublimates at a relatively low temperature compared to other solids.
7. What safety equipment is necessary for this experiment?
   Answer: Safety goggles and gloves are necessary to protect against potential burns and irritation.
8. Why is ventilation important in this experiment?
   Answer: Proper ventilation ensures that any gases produced are safely dispersed, reducing inhalation risks.
9. What change is observed when Ammonium Chloride sublimates?
   Answer: Ammonium Chloride changes from a solid directly to a gas and then back to a solid upon cooling.
10. How does temperature affect the rate of sublimation of Ammonium Chloride?
    Answer: Higher temperatures increase the rate of sublimation.
11. Can sublimation be reversed?
    Answer: Yes, sublimation can be reversed by cooling the gas back into a solid without going through the liquid phase.
12. What is the physical state of Ammonium Chloride at room temperature?
    Answer: At room temperature, Ammonium Chloride is a solid.
13. How do you know when Ammonium Chloride has sublimated?
    Answer: You can tell it has sublimated when you see it depositing on the cooler parts of the apparatus, indicating it has changed from solid to gas and back to solid.
14. What role does the Bunsen burner play in this experiment?
    Answer: The Bunsen burner provides the heat necessary to cause the sublimation of Ammonium Chloride.
15. What is the chemical formula of Ammonium Chloride?
    Answer: NH4Cl.
16. Why must the test tube be clamped during the experiment?
    Answer: To ensure stability and prevent accidents since the test tube becomes hot and could be a hazard if held by hand.
17. Is sublimation a common property of all solids?
    Answer: No, not all solids sublimate; it is a property specific to certain chemicals like Ammonium Chloride and dry ice.
18. What is the result of the sublimation process in this experiment?
    Answer: The result is the direct transition of Ammonium Chloride from solid to gas and then back to solid form upon cooling.
19. What could prevent the correct observation of sublimation?
    Answer: Insufficient heat, improper setup, or poor visibility in the test tube could prevent correct observation.
20. Why is it important to handle all chemicals with care during the experiment?
    Answer: To prevent chemical burns, inhalation of fumes, and other safety hazards associated with laboratory chemicals.

Multiple Choice Questions (MCQs)

1. Which of the following substances commonly undergoes sublimation?
   • a) Sodium Chloride
   • b) Ammonium Chloride
   • c) Copper Sulfate
   • d) Potassium Bromide
   • Answer: b) Ammonium Chloride
2. What is the primary purpose of using a watch glass in this sublimation experiment?
   • a) To increase the temperature
   • b) To measure the amount of sublimated material
   • c) To collect the sublimated material
   • d) To prevent the material from sublimating
   • Answer: c) To collect the sublimated material
3. Which of the following is a necessary safety precaution when performing the sublimation experiment?
   • a) Use of a magnetic stirrer
   • b) Use of protective gloves and goggles
   • c) Addition of a buffering agent
   • d) Performing the experiment in direct sunlight
   • Answer: b) Use of protective gloves and goggles
4. At which stage of the experiment is heat applied?
   • a) Before placing the Ammonium Chloride in the test tube
   • b) After sealing the test tube
   • c) During the collection of sublimated Ammonium Chloride
   • d) To the bottom of the test tube containing Ammonium Chloride
   • Answer: d) To the bottom of the test tube containing Ammonium Chloride
5. What indicates that sublimation of Ammonium Chloride has occurred?
   • a) The substance dissolves completely
   • b) Formation of a liquid layer in the test tube
   • c) Deposition of solid on the cooler parts of the apparatus
   • d) Change in the color of the substance
   • Answer: c) Deposition of solid on the cooler parts of the apparatus