Part D- Selection of a Recrystallization Solvent • The instructor provided us with a test tube filled with an unknown amount of an unknown substance, we were to determine which of two solvents, water or ethanol, would work best to perform a recrystallization to purify the unknown solute. At first, 20 mL of 95% ethanol was added to a portion of the sample on a separate test tube, but the solution almost completely dissolved in the solvent, and after some light stirring the solute was all dissolved at room temperature. This solution was disposed of and 20 mL of water were added to the remaining sample in the original test tube. After introducing the water, it was clear the solution had not dissolved, so a hot plate and hot bath were set up in …show more content…
It can be said with security that the resulting solid from the recrystallization is pure benzoic acid because the observed melting point range of said solid was found to be 122.2-124.9 °C, and the accepted value for benzoic acid’s melting point is 122 °C1. The close proximity of these values means the solid found at the end of the procedure is fairly pure, however, there is a slight deviance from the accepted value which can probably be attributed to a miniscule amount of impurity left on the sample, a possible way to alleviate this would be to properly wash and dry the resulting solid, making sure to be as thorough as possible. As pure as this compound is, the fact that only 57.4 % of the original sample was recovered is rather alarming, some of the lost sample can be attributed to the use of decolorizing carbon as it has been reported to cause a loss of sample2 (which could be alleviated by using a minimum amount depending on the amount of colorant and not consistently 0.05 g) but that still is not solely responsible for the loss of that much sample. A very probable reason for the loss of sample can be my own fault, the solution should have been left in the hot plate much longer, I must have removed prematurely by writing off some actual benzoic acid as negligible impurities, because of this some benzoic acid was stuck with the impurities that were disposed of in the …show more content…
Out of the three experiments so far, this one is the one with the most favorable results, providing a yield of 87.1% and more-so the fact that the melting point range of 140.1-142.4 °C included the value 142 °C, which is the accepted melting point of dimethyl terephthalate. More staggering is the narrowness of the melting point range, which emphasizes the fact that the purification was very favorable, as was the resulting yield. A yield of 87.1% is quite far from the norm of the results from the last experiment, and I would attribute the overall success of this experiment to the fact that there was a trend of improvement as more experiments were done, as well as the rather tricky nature of ethanol and the dimethyl terephthalate, which prompted me to be extremely careful and vigilant to the dissolution of the solute. However, there is still a discrepancy in the yield that can be attributed, once again, to the fact that carbon causes some loss of