National University of Singapore Essay

The way of the yellow crystals obtained tallies with the reference physical appearance of Dibenzalacetone1. The appearance of the white powder obtained also tallies with the reference physical appearance of o-Chlorobenzoic acid2. The yields of the compounds are relatively low at 34.2% and 29.5%. This may be out-of-pocket to some possible sources of error and limitations which will be discussed in the next section. Limitations and Sources of phantasmLoss of compounds was an important factor that fountaind the yield of the purified compounds to be reduced. This may bring occurred first during the extraction phase where extraction may not be complete. During the filtration and nothingness filtration processes, there was also a high level of difficulty in retrieving all the wanted products due to the products forming on the edges of the filter paper or gummy to the sides of the apparatus. Although the yield can be improved by increasing the number of extractions, the increase will not be significant enough (explained under habit question 1) to overcome the loss of the compounds due to frequent transferring of the products.The usage of the separatory funnel to separate the 2 organic and aqueous layers limited the accuracy of the experiment due to potential contamination. There was difficulty in determining the exact boundaries between the organic and aqueous layers accurately even under precautions such as conducting the withdrawal at slow speed and at eye level.Contamination of the purified products will cause the melting point determination to deviate from actual results and identifying the compounds incorrectly. The solubility demonstrate conducted to determine the recrystallization solvent might be another possible source of error. The amount of compound to be added into 2mL of the solvent was estimated rather than accurately weighed. This may have cause errors in determining the solubility of the compounds in the solvents and hence, led to incorrect u se of the proper recrystallization technique for the compounds. Furthermore, cloudy mixtures obtained upon mixing the compound and the solvent might cause the solubility of the compounds to be inaccurately determined. ConclusionA mixture of 2 organic compounds was separated utilise recrystallization and purified. Melting Point Determination was the method used to identify the 2 organic compounds and cross-checking the experimental results obtained with a list of possible organic compounds showed that the Neutral Compound was Dibenzalacetone and the Acidic Compound was o-Chlorobenzoic acid. Verifying the identified compounds via their appearances with references supercharge validated the experimental results. References1. Royal Society of Chemistry, Chemspider, Search and Share Chemistry http//www.chemspider.com/Chemical-Structure.86113.html, Retrieved 14 September 2013 2. Royal Society of Chemistry, Chemspider, Search and Share Chemistry http//www.chemspider.com/Chemical-Structure .8071.html, Retrieved 14 September 2013 Exercise QuestionsQuestion 1a) D = Xo / XwWhen D = 8, Ao = 8 AwSince mass can be expressed as a product of tidy sum and concentration as shown in Equation 1 below, by letting Vo be the volume of organic layer, Vw thevolume of aqueous layer with m organism the total initial mass of A, Equation 2 can be obtained. - Equation 1- Equation 2Using Equation 2 and interchange in known values, we can obtain- Equation 3Solving, we get Aw = 1.11 X 10-2 g/mLb) Using Equation 2,For 1st Extraction,- Equation 4Solving, we get Aw = 2.00 X 10-2 g/mLFor 2nd Extraction,- Equation 5Solving, we get Aw = 4.00 X 10-3 g/mLc) Repeating the above method as shown in (b) for multiple extractions, we can obtain For 4th Extraction using 20 mL of dichloromethane,Aw = 1.23 x 10-3 g/mLFor 8th Extraction using 10 mL of dichloromethane,Aw = 3.91 X 10-4 g/mLd) Based on calculation above, while the total amount of dichloromethane used in (a), (b) and (c) remained eonian at 80 m L, the values of Aw obtained decreases with increasing number of extractions done with smaller amounts of dichloromethane used during each extraction. Multi-extraction allows more of the solute to dissolve in the solvent. This leads to a higher(prenominal)(prenominal) amount of solute extracted.e) To access if excessive extraction (8 times) is necessary, the yield difference of solute extracted between doing 4 and 8 times extraction must be considered.Mass of solute not extracted by 4-times Extraction = 1.23 X 10-3 X 80= 0.0984 gMass of solute not extracted by 8-times Extraction = 3.91 X 10-4 X 80= 0.0313 g parting yield of solute using 4-times Extraction == 98.8%Percentage yield of solute using 8-times Extraction == 99.6%The percentage yield increases by 0.8% which is not very significant as figure above. This does not justify the cost and time needed to carry out excessive extraction since the yield difference is small. Question 2c) A intermit solvent for recrystallization of B will give a higher yield of B crystals. Based on the calculation in (a) and (b), water gives a higher yield of crystals (8.54 g at 25C and 9.81 g at 0C ) as compared to ethanol (7.38 g at 25C and 8.21 g at 0C). Hence, water is a better solvent for the recrystallization of B.d) The crystals should be washed with frigid solvent (0C). The solubility of compounds increases with increasing temperature. Washing the crystals with cold solvent ensures that the crystals do not dissolve back into the solvent. Washing the crystals with warm solvent will cause the yield of crystals to diminish.