National University of Singapore Essay

The manner of the yellow crystals harbored tallies with the reference physical behavior 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 whitethorn be overdue to some possible radicals of error and limitations which will be discussed in the future(a) section. Limitations and Sources of ErrorLoss of compounds was an important factor that exercised the yield of the purified compounds to be reduced. This may have occurred first during the extraction phase where extraction may not be complete. During the filtration and vacuum filtration processes, there was also a high aim of difficulty in retrieving all the wanted products due to the products forming on the edges of the riddle paper or sticking to the sides of the apparatus. Although the yield thrust notice be improve by increasing the number of extractions, th e increase will not be satisfying enough (explained under exercise question 1) to overcome the dismissal of the compounds due to frequent transferring of the products.The usage of the separatory funnel to separate the 2 innate and sedimentary 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 separation 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 falsely. The solubility strain conducted to determine the recrystallization root might be another possible source of error. The totality of compound to be added into 2mL of the answer was estimated rather than accurately weighed. This may have ca utilise errors in determining the solubility of the compounds in the consequences and hence, led to incorrect use 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 apply recrystallization and purified. Melting stay 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 vitriolic Compound was o-Chlorobenzoic acid. Verifying the identified compounds via their appearances with references further validated the experimental results. References1. munificent Society of Chemistry, Chemspider, Search and Share Chemistry http//www.chemspider.com/Chemical-Structure.86113.html, Retrieved 14 September 2013 2. purple Society of Chemistry, Chemspider, Search and Share Chemistry http//w ww.chemspider.com/Chemical-Structure.8071.html, Retrieved 14 September 2013 work on headersQuestion 1a) D = Xo / XwWhen D = 8, Ao = 8 AwSince mass can be expressed as a product of volume and submerging as shown in Equation 1 below, by letting Vo be the volume of organic layer, Vw thevolume of aqueous layer with m beingness the kernel initial mass of A, Equation 2 can be obtained. - Equation 1- Equation 2Using Equation 2 and subbing in known values, we can obtain- Equation 3Solving, we get Aw = 1.11 X 10-2 g/mLb) Using Equation 2,For initiatory Extraction,- Equation 4Solving, we get Aw = 2.00 X 10-2 g/mLFor second Extraction,- Equation 5Solving, we get Aw = 4.00 X 10-3 g/mLc) iterate 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 computation above, while the total amount of dichloromethane used in (a) , (b) and (c) remained constant at 80 mL, 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 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. circle 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 gPercentage 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 calculated above. This does not justify the cost and time essential to carry out excessive extraction since the yield difference is small. Question 2c) A better 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 swear out with cold 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.