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Eric Echeandia TA Bill Zhou Organic Chemistry Lab (Mondays: 5-8:50pm) 27 September 2017

The main goal for the first experiment was to recrystallize phthalic acid. Recrystallization is a common laboratory technique utilized to purify chemicals. The main concept behind the recrystallization is dissolving a solid compound with impurities in an appropriate solvent (by mixing, heating or both) and then allowing it to recrystallize by cooling the solution (by using an ice bath or another cooling method.) When the compound of interest is recrystallizing, the impurities are excluded; thus, a pure compound arises. In terms of the phthalic acid, in the experimental part, after following the procedure for recrystallization and letting it dry for a week, 79.4% was recovered through the recrystallization. In terms of the volume of water actually used to dissolve the phthalic acid versus the one calculated, the one calculated is actually less than the one utilized. For instance, for one gram of phthalic acid, 5.56 mL of water should be utilized; however, 10mL of water were utilized in the lab. The second part of the experimental portion was to find an appropriate compound for recrystallization of phthalic acid; a good compound has to be able to dissolve in solvent when heated and create crystals when cooled in ice bath. Methanol, ethanol, acetone, acetic acid, water, toluene and ligroin were utilized for dissolving benzoic acid and resorcinol. In terms of the benzoic acid, it fully dissolved at room temperature in ethanol and acetone. When heated, it fully dissolved in methanol and acetic acid. Finally, benzoic acid was slightly soluble when heated in toluene and ligroin. In all of the solvents (except water,) benzoic acid formed crystals: in some powdery crystals, in others paste-like crystals. In terms of the resorcinol, it was fully soluble at room temperature in methanol, ethanol, acetone, water and toluene. It was fully soluble in acetic acid, when heated. Finally, it was slightly soluble when heated in ligroin. With the exception of the precipitates and powdery crystals in toluene and ligroin, respectively, resorcinol did not produce any precipitate in the

solvents. From the Spartan molecule models and the observations gathered, it was learned that like dissolves like; molecules need to have same polarity to be dissolved. This explains why the polar benzoic acid dissolved in methanol and acetic acid when heated; both acetic acid and methanol are polar because of their respective hydroxyl groups. The second experiment’s main goal was to find the melting point of benzoic acid, succinimide and trans-stilbene. Learning the melting point of different compounds is important because it helps identify unknown substances. Also, it might be important to know the melting point of a compound to determine its purity. In this experiment, the DigiMelt was utilized to obtain the melting ranges of the three compounds and the three compounds with an unknown substance. Following the appropriate procedure, the melting ranges were obtained. Benzoic acid had a melting range from 120.8˚C to 124.8˚C, succinimide had a melting range from 120.3˚C to 122˚C, and transstilbene had a melting range from 118˚C to 126˚C. After the unknown 102N was added to each of the known substances in a 1:1 ratio, the melting ranges were obtained: benzoic acid+102N was from 119.5˚C to 123.8˚C, succinimide+102N was from 104.5˚C to 112˚C, and trans-stilbene was from 104.2˚C to 111.2˚C. After observing the different ranges with and without the unknown substance, it is evident that the compound 102N was benzoic acid; benzoic acid’s and benzoic acid+102N’s melting ranges were very similar. The last portion of the experiment was to collect pure cholesterol from synthetic gallstones. This was done using evaporation, filtration and recrystallization. From 1.007g of gallstones, only 0.023g was recovered, for a recovery rate of 2.28%. Because the melting range of this compound was from 116˚C to 126˚C, it is deducted that the cholesterol is not pure, for pure cholesterol has a melting range of 148˚C to 150˚C. This is attributed to the fact that gallstones are only 55-75% cholesterol.

Overall, sources of error include spilling crystals, inadequate cleaning of the rods, and faulty filtration. Finally, solutions could have been spilled while transferring from different beakers or flasks and not allowing enough time in ice baths for substances to recrystallize....