Testing Unknown Compounds: Bromination, Tollen's, Solubility, Ceric, IR & More - Essay Sample

Introduction

The experiment achieves its objective by completing tests like Bromination test for unsaturation, Tollen's test for aldehydes, solubility test, Ceric test for alcohol, melting point test for solid, IR spectrum test for liquid. The unknown compounds liquid 11 and solid (I) went through the tests one by one, and a narrowing down is done after every type of test. The solubility test for the liquid demonstrated the unknown liquid as soluble in water to form a pH scale of 6. Organic compounds that contain less than five carbons and have oxygen functional group are soluble in water, and this kind includes carboxylic acids, aldehydes, ketones and alcohols, these are clues for the unknown liquid 11. Larger molecular compounds do not dissolve in water. The pH of 6 was close to that of a neutral solution of pH 7. Aldehydes, alcohols, and ketones form a better clue of the unknown liquid. The unknown solid (I) was not soluble in water but was soluble in 6M NaOH. A compound that is soluble in NaOH but not soluble in water is identified as a carboxylic acid containing more than five carbons. The acid is soluble as a result of the formation of the soluble sodium salt of the present carboxylic acid when neutralization is done. Aspirin and acetylsalicylic acid are some examples of this kind of a functional group. The other compounds like hexane and hexanoic acid were soluble in water. Aniline, however, was not soluble in both water and 6M NaOH (Varsel, 2011).

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For the Tollen's test, the colors of the compounds are vital for the experiment. The unknown liquid 11 is light yellow the unknown solid (I) is white sand in color. Glucose and the unknown liquid gives a positive result for the test, silver mirror color is seen during the reaction. A compound with a carbonyl functional group has carbon at the terminal. The reaction between the silver ion and the unknown in ammonia environment to produce a silver mirror precipitate is identified as an aldehyde. The unknown liquid 11 is indeed an aldehyde. The unknown solid (I) gave a negative result in Tollen's test. A silver mirror was not formed instead a white foam formed at the bottom (Chakraborty, 2009) A negative result for the Tollen's test shows that the carbonyl function group of the compound is located at the non-terminal point a structure exhibited by ketones.

The bromination test uses bromine which is an alkalide whose reaction with acid is invalid. For this reason, the unknown solid (I) which may be a possible acid is null for the test. The Bromination test for the unknown liquid 11 was done alongside with pentene an alkene with five carbons. The test proves the presence of unsaturation in hydrocarbons. It only took a few drops of bromine for the pentene to stay clear but the unknown liquid became cloudy, this is a negative test for Bromination. A compound with a carbon-carbon double bond is an unsaturated compound called alkene. Adding bromine to alkene results to the bromine discoloration since it is added to the double bond. The red color of bromine is absorbed by the alkene to produce a clear solution, and so the unknown liquid 11 is not an alkene, there is no carbon-carbon double bond in it.

The Ceric Nitrate test is used to identify the alcohol functional group in the unknown compound. The datum for the test included n-propanol alcohol which gives a positive result for the test with brown color in the reaction. Unknown solid (I) gave a positive result with red color in the reaction. The unknown liquid 11 gave a negative result with a dark yellow color in the reaction. Alcohols react with the yellow Ceric Nitrate reagent to provide a change of color from yellow to red. The carbonyl group, on the other hand, is unreactive. The experiment, therefore, tests for the presence or absence of the alcohol. During the reaction of Ceric Nitrate and alcohol, the groups attached to the inorganic compound are changed causing the color change which indicates the presence of alcohol. The unknown liquid 11, therefore, has a carbonyl functional group and is not an alcohol. The presence of a hydroxyl group in alcohol in the solid was confirmed by the color change which gives a stronger clue for the unknown solid (I). From the tests above, the unknown solid was concluded to be a carboxylic acid and the unknown liquid to be an aldehyde. The two were to go a further test for a more accurate confirmation, that is, melting point test for the unknown solid (I) against a possible solids such as Acetylsalicylic acid, boric acid, dodecyl alcohol, glucose, and benzoic acid ,and the IR spectrum test for the unknown liquid 11 against the possible liquid heptaldehyde.

The melting point test for the solids is very concise in identifying unknown solids by merely giving a comparison to the melting points of other solids tested (Jackson, 1990). The unknown solid (I) has a melting point of 138oC which is very close to that of acetylsalicylic acid having a melting point of 135oC. The unknown liquid 11 is identified as heptaldehyde since it came in very close to its IR. The infrared spectra of-heptaldehyde in the skeletal bending and stretching regions are sharp which is exhibited by the unknown liquid 11 too. The skeletal stretching modes in the region 3000-1500 cm-1, with probably some of the lower-frequency carbon-hydrogen bending are modes, are observed. Both the solutions had the highest peak at about 2900 cm-1 in which a carbon-hydrogen bond is stretching. Another peak recorded at about 1700 cm-1 where carbon-oxygen bond stretches (Novak, 2000). The unknown liquid 11 is heptaldehyde.

Conclusion

In summary, the unknown solid (I) was concluded to be acetylsalicylic acid since it had a melting point of 138oC which is close to 135oC. It is soluble in NaOH but not in water which means it is a carboxylic acid and also tested negative for the Tollen's test. The Ceric Nitrate test proved positive for the solid which shows that it contains hydroxyl group present in the alcohols and carboxylic acids. The method of deciding whether the unknown solid (I) was concise since by knowing the melting point of the acetylsalicylic acid and comparing to the unknown solid it becomes easy to deduce. The difference was not much as compared to all other solids, and so the unknown solid is acetylsalicylic. The unknown liquid 11 is concluded to be heptaldehyde since it shows close IR spectrum test behavior to the liquid. The Tollen's test and its solubility in water indicate that it is indeed an aldehyde but not an alkene according to bromination test. Finally, the Ceric Nitrate test by giving a negative result means it is not an alcohol. The concise confirmation comes during the IR spectrum test against the heptaldehyde and proved it is heptaldehyde.

References

Varsel, C. J., Morrell, F. A., Resnik, F. E., & Powell, W. A. (2011). Qualitative and Quantitative Analysis of Organic Compounds. Use of Low-Voltage Mass Spectrometry. Analytical Chemistry, 32(2), 182-186. Retrieved from (https://pubs.acs.org/doi/pdf/10.1021/ac60158a011)

Chakraborty, D., Gowda, R. R., & Malik, P. (2009). Silver nitrate-catalyzed oxidation of aldehydes to carboxylic acids by H2O2. Tetrahedron Letters, 50(47), 6553-6556. Retrieved from (https://pubs.acs.org/doi/abs/10.1021/ac60158a011?journalCode=ancham)

Novak, A., & Whalley, E. (2000). THE INFRARED SPECTRA AND STRUCTURE OF POLYALDEHYDES: IV. THE HIGHER POLYALDEHYDES. Canadian Journal of Chemistry, 37(10), 1718-1721.Retrieved from (https://www.nrcresearchpress.com/doi/pdf/10.1139/v59-248)

Jackson, C. L., & McKenna, G. B. (1990). The melting behavior of organic materials confined in porous solids. The Journal of Chemical Physics, 93(12), 9002-9011. Retrieved from (https://aip.scitation.org/doi/abs/10.1063/1.459240)