Determination of boiling point of an organic compound

Determination of boiling point of an organic compound in a pitch lab experiment is a fundamental analytical technique used to identify and characterize organic substances. This experiment helps students understand the physical properties of organic compounds and their behavior under different temperature conditions.

Aim

To determine the boiling point of an organic compound using a pitch lab setup and verify the experimental result with theoretical values.

Apparatus Required

• Thiele's tube or pitch tube
• Boiling point apparatus
• Thermometer (0-360°C)
• Glass capillary tube
• Rubber cork with hole
• Bunsen burner or heating mantle
• Test tube or boiling tube
• Organic compound sample (naphthalene, benzene, or toluene)
• Wire gauze
• Tripod stand
• Safety goggles and gloves

Theory

The boiling point of an organic compound is defined as the temperature at which the vapor pressure of the liquid equals the atmospheric pressure surrounding it. At this point, bubbles of vapor form within the liquid and rise to the surface.

Key Concepts:

• Boiling point is a characteristic physical property of organic compounds
• Molecular weight and intermolecular forces affect boiling points
• Purity of compound influences the sharpness of boiling point
• Pure compounds have sharp, well-defined boiling points
• Impure compounds show a range of boiling temperatures

Procedure

Step-by-Step Method:

1. Setup Preparation

   • Clean and dry the Thiele's tube thoroughly
   • Fill the tube with liquid paraffin or silicone oil up to 2/3 of its height

2. Sample Preparation

   • Take a small amount of organic compound in a test tube
   • Insert a sealed capillary tube open-end down into the sample
   • Ensure the compound covers the capillary tube completely

3. Assembly

   • Attach the thermometer to the test tube using a rubber band
   • Place the setup in the Thiele's tube
   • Ensure the thermometer bulb is at the same level as the sample

4. Heating Process

   • Heat the Thiele's tube gently using a Bunsen burner
   • Heat uniformly to ensure proper circulation of the heating liquid
   • Observe the formation of bubbles in the capillary tube

5. Observation

   • Note the temperature when continuous bubble formation begins
   • Record the temperature when bubble formation stops
   • The boiling point is the temperature at which bubble formation ceases

Observation Table

Result

The boiling point of the organic compound is determined to be [Record observed temperature]°C.

Verification:

Compare the experimental value with standard literature values:

• Benzene: 80.1°C
• Toluene: 110.6°C
• Naphthalene: 218°C

Percentage Error = [(Experimental Value - Theoretical Value)/Theoretical Value] × 100

Precautions

1. Safety First

   • Wear safety goggles and gloves throughout the experiment
   • Handle organic compounds in a well-ventilated area

2. Apparatus Handling

   • Ensure the Thiele's tube is thoroughly cleaned and dried
   • Use clean and dry capillary tubes for accurate results

3. Heating Control

   • Heat the setup gently to avoid bumping
   • Maintain uniform heating for proper temperature distribution
   • Never overheat the organic compound

4. Measurement Accuracy

   • Keep the thermometer bulb immersed at proper depth
   • Read the thermometer at eye level to avoid parallax error
   • Record temperature when it becomes steady

5. Chemical Handling

   • Handle flammable organic compounds away from open flames
   • Use minimal quantities of organic compounds
   • Dispose of chemicals as per laboratory guidelines

Viva Voce Questions and Answers

Q1: What is the principle behind boiling point determination?

A: The principle is based on the fact that a liquid boils when its vapor pressure equals atmospheric pressure. At this temperature, bubbles of vapor form within the liquid.

Q2: Why is a sealed capillary tube used in this experiment?

A: The sealed capillary tube allows us to observe when the vapor pressure of the liquid equals atmospheric pressure. Bubbles form and escape when boiling point is reached.

Q3: What factors affect the boiling point of organic compounds?

A: Factors include:

• Molecular weight
• Intermolecular forces (hydrogen bonding, dipole-dipole interactions)
• Molecular structure and branching
• Atmospheric pressure

Q4: How does impurity affect boiling point determination?

A: Impurities generally elevate the boiling point and make it less sharp. Pure compounds have sharp, well-defined boiling points.

Q5: Why is Thiele's tube used instead of direct heating?

A: Thiele's tube provides uniform heating and prevents localized overheating. The liquid medium ensures even temperature distribution.

Q6: What is the significance of boiling point determination?

A: Boiling point determination helps in:

• Identifying unknown organic compounds
• Assessing purity of compounds
• Characterizing organic substances
• Understanding intermolecular forces

Q7: How can you verify the purity of a compound using boiling point?

A: Pure compounds have sharp, constant boiling points. Impure compounds show a range of boiling temperatures or elevated boiling points.

Q8: What modifications can be made for compounds with high boiling points?

A: For high boiling point compounds:

• Use high-temperature oil as heating medium
• Employ reduced pressure techniques
• Use specialized high-temperature apparatus

Conclusion

The determination of boiling point of an organic compound in a pitch lab experiment is an essential analytical technique that provides valuable information about the identity and purity of organic substances. This experiment demonstrates fundamental principles of physical chemistry and develops practical laboratory skills in temperature measurement and observation techniques.

The experiment requires careful attention to safety protocols and precise temperature control to obtain accurate results. Proper understanding of the theoretical background ensures better interpretation of experimental observations and helps in troubleshooting common experimental issues.

This comprehensive guide on boiling point determination serves as a complete reference for students performing pitch lab experiments in organic chemistry laboratories.