Identification of Unknown Organic Compounds: Experiment Report

Abstract

The main objective of this lab was to identify two unknown organic compounds, one solid and one liquid, using various methods including melting point (M.P), boiling point (B.P), Infrared spectroscopy (I.R), elemental analysis, and the determination of the Index of Hydrogen deficiency (IHD). The physical properties of the compounds, such as color, odor, melting point, and boiling point, were also examined to gain insight into their characteristics.

Introduction

Identification of unknown organic compounds is a fundamental task in chemistry.

It is crucial to determine the composition, structure, and functional groups present in these compounds. In this lab, we employed several techniques to achieve this goal, including melting point and boiling point determination, Infrared spectroscopy, elemental analysis, and calculation of the Index of Hydrogen deficiency (IHD).

The functional group of a compound can be determined using Infrared spectroscopy, which provides a spectra based on the chemical bonds present in the compound. The Index of Hydrogen deficiency (IHD) helps determine the degree of saturation in a compound, indicating the presence of double bonds, triple bonds, or rings.

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Elemental analysis is a powerful method for determining the molecular formula of a compound by analyzing its elemental composition. Additionally, the boiling point and melting point of a compound are crucial physical properties that can confirm its hypothetical structure.

Materials and Methods

The following equipment and materials were used in the experiment:

Experimental Procedure

Two unknown organic compounds, one solid and one liquid, were provided for analysis.

The following procedures were performed:

1. For the solid compound:
   1. A sample of the crystalline solid was taken in a bulb of a capillary tube.
   2. The capillary tube was inserted into the electric melting point apparatus.
   3. The temperature was increased at a rate of 1-2°C/min.
   4. The initial temperature was noted when the first tiny drop of liquid appeared.
   5. The final temperature was noted when all the crystals had completely melted.
2. For the liquid compound:
   1. 0.5-1.0 ml of the liquid was taken in a clean test tube.
   2. The test tube was clamped and held on top of a heating mantle.
   3. A thermometer was placed 2 cm above the liquid with another clamp.
   4. The initial temperature was recorded when the first bubble appeared, and the final temperature was recorded when there was vigorous movement in the liquid.
3. Both the solid and liquid samples were scanned using a NICOLET iS5 FTIR spectrometer. The surface was cleaned thoroughly with acetone, and the background spectrum was collected before the sample spectra.

Results

The results of the analysis are summarized in the following table:

The empirical formula of the solid compound obtained from elemental analysis and composition was determined to be C₇H₆O₂. The calculated Index of Hydrogen deficiency (IHD) for this compound was 5, indicating the presence of 4 double bonds and 1 ring. The experimental melting point of the solid compound was 116.7°C, which was close to the reference value of 122.41°C. Any discrepancies could be attributed to impurities in the sample container.

The liquid compound was found to have an empirical formula of C₅H₁₀O. The calculated IHD for this compound was 1, suggesting the presence of either 1 ring or a double bond. Experimentally, the boiling point of the liquid compound (2-Pentanone or acetone) was determined to be 95°C, while the reference value was 101°C. The difference in boiling point could be attributed to impurities in the test tube.

Discussion

The results of the analysis indicate that the solid compound is likely benzoic acid (C₇H₆O₂) due to its empirical formula and IHD of 5. The experimental melting point was in good agreement with the reference value, confirming the identity of the compound. Any variation in the melting point may be attributed to impurities in the sample.

For the liquid compound, the empirical formula C₅H₁₀O and an IHD of 1 suggested the presence of either a ring or a double bond. The strong smell and the similarity of the IR spectra to 2-Pentanone indicated that the compound was indeed 2-Pentanone. The experimental boiling point was slightly lower than the reference value, which may be due to impurities in the test tube.

Conclusion

In this lab, two unknown organic compounds, one solid and one liquid, were successfully identified using various techniques, including melting point, boiling point, Infrared spectroscopy, elemental analysis, and the determination of the Index of Hydrogen deficiency (IHD). The solid compound was determined to be benzoic acid (C₇H₆O₂), while the liquid compound was identified as 2-Pentanone (C₅H₁₀O).

The experimental results for the melting and boiling points were consistent with the reference values, with minor discrepancies that could be attributed to impurities in the samples. Overall, the identification of these unknown compounds demonstrates the importance of various analytical techniques in organic chemistry.

Recommendations

For future experiments of this nature, it is essential to ensure the cleanliness and purity of equipment and containers to minimize potential sources of error. Additionally, repeating the experiments with different batches of the unknown compounds and comparing the results can provide more confidence in the identification process.