Determine the Melting point of Biphenyl

 Abstract

This experiment aims to determine the melting point of biphenyl using a melting point apparatus. Melting point is a characteristic property of a substance and is useful in identifying and characterizing compounds.

Introduction

The melting point of a substance is the temperature at which it changes from a solid to a liquid phase. It is a unique physical property that helps identify and characterize substances. Biphenyl is an organic compound commonly used in research and industrial applications. Determining its melting point is essential for quality control and purity assessment.

Details of the Experiment

Procedure

1. Place a small amount of biphenyl in a capillary tube.
2. Secure the capillary tube in the melting point apparatus.
3. Gradually heat the biphenyl while observing it through a magnifying lens.
4. Record the temperature range at which biphenyl starts to melt and completely melts.

Observations and Calculations

Record the temperature range when biphenyl starts to melt (initial melting point) and when it completely melts (final melting point).

Conclusion

The experimentally determined melting point of biphenyl should closely match its known melting point if the substance is pure.

Precautions

• Handle biphenyl with care as it may be harmful if ingested or inhaled.
• Avoid overheating to prevent decomposition of biphenyl.
• Use safety equipment such as gloves and goggles.

Short Questions with Answers

1. Define melting point.
   Answer: Melting point is the temperature at which a solid changes into a liquid at atmospheric pressure.
2. Why is it important to use a small amount of sample in the melting point determination?
   Answer: To ensure accurate observation of the melting point.
3. What factors can affect the melting point of a substance?
   Answer: Purity of the sample, pressure, and presence of impurities.
4. Why should the heating be gradual during the melting point determination?
   Answer: To prevent rapid heating and ensure accurate measurement of the melting point.
5. How can impurities affect the observed melting point?
   Answer: Impurities can lower and broaden the melting point range.
6. What is the significance of recording the temperature range during melting?
   Answer: It provides a more accurate determination of the melting point.
7. What precaution should be taken to ensure accurate melting point determination?
   Answer: The sample should be dry and free from contaminants.
8. What is the purpose of using a melting point capillary tube?
   Answer: To contain a small amount of sample for observation.
9. How does the melting point of biphenyl compare to its literature value?
   Answer: The experimental melting point should closely match the literature value for pure biphenyl.
10. What should be done if the sample shows signs of decomposition during heating?
    Answer: Stop heating immediately to prevent inaccurate results.
11. What is the primary source of error in melting point determination?
    Answer: Presence of impurities in the sample.
12. How can the accuracy of melting point determination be improved?
    Answer: By using a pure sample and calibrating the apparatus properly.
13. What safety precautions should be followed during the experiment?
    Answer: Wear protective gear and handle hot equipment with care.
14. What does the appearance of a melting point plateau indicate?
    Answer: It indicates that the sample is melting uniformly.
15. What should be done if the melting point range is too broad?
    Answer: Repeat the experiment with a smaller sample size.
16. What is the purpose of observing the sample through a magnifying lens?
    Answer: To accurately detect the onset of melting.
17. What happens to the melting point of a substance if pressure is increased?
    Answer: The melting point increases.
18. How does the melting point of biphenyl compare to that of other aromatic compounds?
    Answer: Biphenyl typically has a higher melting point compared to other aromatic compounds.
19. What is the effect of impurities on the observed melting point?
    Answer: Impurities lower and broaden the observed melting point range.
20. Why is it important to use a heating rate within a specified range during the experiment?
    Answer: To ensure consistent and reproducible results.

Multiple Choice Questions (MCQs) with Answers

1. What does the melting point of a substance indicate?
   • a) Temperature at which the substance decomposes
   • b) Temperature at which the substance evaporates
   • c) Temperature at which the substance changes from solid to liquid
   • d) Temperature at which the substance reacts with air
   • Answer: c) Temperature at which the substance changes from solid to liquid
2. Why is it important to record both initial and final melting points?
   • a) To ensure accurate measurement
   • b) To calculate the average melting point
   • c) To confirm the purity of the substance
   • d) All of the above
   • Answer: d) All of the above
3. What is the purpose of using a magnifying lens during the experiment?
   • a) To observe the substance more closely
   • b) To measure the temperature more accurately
   • c) To prevent contamination
   • d) To enhance safety
   • Answer: a) To observe the substance more closely
4. Which safety equipment is essential during the experiment?
   • a) Lab coat
   • b) Safety goggles
   • c) Rubber gloves
   • d) All of the above
   • Answer: d) All of the above
5. What precaution should be taken to avoid overheating of biphenyl?
   • a) Increase the heating rate
   • b) Decrease the heating rate
   • c) Use a higher melting point apparatus
   • d) None of the above
   • Answer: b) Decrease the heating rate