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Introduction

Title:- Recrystallization Objective:- * The first part of the experiment is to introduce us to a technique called recrystallization. This technique can be used to purify solids. * To chose the most appropriate solvent to obtain a successful recrystallization of benzoic acid. * To determine the percentage recovery. * To determine melting point to ensure that the purity of the benzoic acid. Material and Apparatus:- * Benzoic acid * Charcoal * Boiling chips * Distilled water * Ice * Erlenmeyer flask * Beaker * Hot plate * Short-stemmed funnel * Filter paper * Glass rod * Buchner funnel * Rubber tubing (hose) * Spatula * Mel-temp apparatus Procedure:- 1. 2.0 g of crude benzoic acid is weighed into a 125-mL Erlenmeyer flask. The weight of the benzoic acid is recorded to the nearest 0.1 g. 2. The apparatus is kept warm because the solubility of benzoic acid is very sensitive to temperature. 100-200 mL of water is heated to boiling in a beaker on a hot plate (with boiling chips). An Erlenmeyer flask with little water in it (with boiling chips) is also heated, and a short-stemmed funnel is rested in its neck. 3. A filter paper is fluted to fit the funnel. 4. a few boiling chips is added to the benzoic acid, then hot water is started to add until the benzoic acid is dissolved. (Once some water had been added, the flask can be kept on the hot plate to keep it hot). Note that there may be some insoluble crud in the benzoic acid, and the crud will never dissolve, no matter how much water we added. ...read more.

Middle

0.81 Triethylamine -115 90 0.726 1.4010 2.42 33.1 0.87 Trifluoroacetic acid -15 72 1.489 1.2850 8.55 13.7 2.26 2,2,2-Trifluoroethanol -44 77 1.384 1.2910 8.55 12.4 2.52 Water 0 100 0.998 1.3330 80.1 3.7 1.82 o -Xylene -25 144 0.880 1.5054 2.57 35.8 0.62 In general, the higher the dielectric constant of the solvent, the better it will dissolve ionic compounds. Test the solvent on a small amount of the compound. If a solvent doesn't dissolve the crystals when hot, or it readily dissolves the crystals at room temperature, try another solvent. Remember to always use only a minimum amount of hot solvent! In this experiment, water is the best solvent to undergo the recrystallization process of benzoic acid. Because water's boiling point is 100 ?C and water is very polar with the formula H2O. Once you have selected your solvent you are ready to recrystallize your sample. The process of recrystallization can be broken into the following steps: 1. Selection of an appropriate solvent 2. Dissolution of the solute using a minimum amount of hot solvent 3. Decoloration of the solution if necessary (with an activated form of carbon) 4. Removal of suspended solids (through filtration of the hot solution) 5. Crystallization of the solid from the solution as it cools 6. Collecting the purified solid by filtration 7. Washing the crystals with an appropriate solvent to remove impurities 8. Drying the crystals Choosing the solvent The choice of solvent is crucial; by using the best solvent we can obtain the most accuracy result. An essential characteristic of a successful solvent is that the compound be soluble in the hot solvent but insoluble in the cold solvent. ...read more.

Conclusion

Its salt, sodium benzoate, is produced by the neutralization of benzoic acid with sodium bicarbonate, sodium carbonate, or sodium hydroxide. The salt is not found to occur naturally. It is used a preservative in a variety of food products, such as jams, soft drinks, and cereals. Benzoic acid is also an effective food preservative, but its sodium salt is more popular, partly because it is more soluble in water than benzoic acid. The technique can be carried out by dissolving a compound to be purified in a hot solvent (or solvent mixture) and then allowing the solution to cool. If the solvent or solvent mixture is properly chosen, the compound has a decreased solubility at lo lower temperatures, and it will form crystals in the solution. The purity of a solid, and therefore the success of or need for a crystallization procedure, can be determined by taking a melting point. Recall that you used melting point determination in the Thin Layer Chromatograph Chromatography and Melting Point Determination laboratory to identify an unknown nation unknown compound. Precaution step:- * Compound being purified must be insoluble in solvent at room temperature. * Compound must be soluble in boiling solvent. * Solvent's boiling point must be lower than the compound's melting point. * An abundant quantity of crystals must be recoverable from the cool solvent. Conclusion:- * The step by step of the technique recrystallization had been learned. Most of the recrystallization processes undergo this technique. * The most appropriate solvent to obtain a successful recrystallization of benzoic acid is water due to its polarity and 100 ?C boiling points. * Benzoic acid was recrystallized with a 90% recovery using water as the solvent. * The melting point for recrystallized benzoic acid is 119.2 ?C - 120. ...read more.

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