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Identification of an unknown compound.

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Introduction

Identification of an unknown compound Plan An unknown organic compound has been supplied. The organic compound contains one of the following functional groups: - Alcohol - Aldehyde - Carboxylic acid - Ester - Ketone - Phenol In this investigation, the problem that I will attempt to solve is the identity of the unknown compound. This will be achieved by using various spectroscopic techniques (n.m.r, mass spectroscopy, infrared spectroscopy) and a series of experiments. A flow chart has been constructed to identify the unknown compound. A table of results has also been drawn which shows the outcomes of each experiment. The following equipment will be needed for the experiments: - Test tubes - Test tube rack - 10 ml glass pipettes with pipette fillers - 10 ml measuring cylinder - 250 ml glass beaker - Matches - Splint Chemicals As well as the unknown compound the following reagents are required: - Bromine water - 2,4-dinitrophenylhdrazine - Tollens Reagent (0.1moldm-3 silver ions, sodium hydroxide and aqueous ammonia) - Solid metallic sodium - Blue litmus paper Safety The precautions listed below will be followed at all times during the experiments. 1. All coats, bags and personal items will be removed from the work surface to prevent any hazards. 2. A fully buttoned laboratory coat should be worn and a pair of goggles will be worn for eye protection. A pair of latex gloves will also be worn to prevent contact with any chemicals that may irritate the skin. Laboratory coat, goggles and gloves will be worn at all times when handling chemicals. 3. Tie long hair back (if necessary). ...read more.

Middle

The molecular ion is formed when the molecule is ionised (removal of one electron). After observation of the mass spectrum provided it is clear that the molecular ion and hence the Mr of the aldehyde is 44. Knowing the Mr should help in deducing the structure of the aldehyde (types and number of atoms of each element present). Infrared spectroscopy is a technique that identifies the types of functional groups present in an organic molecule. Different functional groups absorb at certain frequencies of infrared radiation. The absorption peaks on an infrared spectrum can help identify the functional groups present in a compound. After analysing the infrared spectrum provided, it is clear that there is a strong sharp absorption peak at approximately 1720 cm-1. This peak indicates the presence of a C=O functional group that is found in aldehydes and ketones. The finding from the infrared spectrum that a C=O group is present supports the results of the chemical tests however an infrared spectrum cannot distinguish between aldehydes and ketones. Nuclear magnetic resonance spectroscopy (nmr) is used to determine the structure of a compound. Peaks on an NMR spectrum occur at different chemical shift values (ppm). The position of the peaks gives information about what proton-containing groups are present. The relative height of the peak provides information on the number of protons (hydrogen atoms) in the group. The splitting pattern of each peak shows the number of protons adjacent to each group. Overall an NMR spectrum provides information on the different groups and how these groups are attached/bonded together in a molecule. ...read more.

Conclusion

Apart from the molecular ion and Mr the mass spectrum does not provide any additional information on compound B, for example, no information on the molecular formula or about the functional groups present in the molecule. Improvements 1. The identity of compound B can be confirmed with another chemical test in future work. This test will involve recrystalising the orange precipitate collected in test 2 and determining the melting point of this precipitate. This technique is used to determine the exact aldehyde present. 2. A wider range of chemical tests will be used to confirm whether compound B is an aldehyde. For example, Fehlings solution can be used as it turns from blue to brick red precipitate in presence of an aldehyde. 3. An improvement would be to gain information of the percentage composition of elements contained in compound B, (by combustion analysis) which would allow calculation of the empirical and molecular formula. Reliability Reliability is a measure of how consistent the observations of the chemical tests are Chemical tests 1 and 2 were only carried out once and therefore it is difficult to say how reliable the observations are. To check whether the outcomes of the test observed were reliable, each test would have to be replicated in future experiments. Test 2 with tollens reagent only produced a faint silver-mirror on the test-tube and this made it difficult to draw inferences. This test was carried out on a second occasion to confirm the initial observation. A silver-mirror was also observed on the second attempt and since the same observation occurred during the first and second attempt, the outcome of this test can be considered reliable. ...read more.

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