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Boiling Point

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De Ocampo, Yves Aaron Julian, Dela Vega, Roderick R. Jr., Elguira, Cedric Tristan D.
Enriquez, Joanne B., Gabat, John Elliot
Group 5, 2D Medical Technology, Faculty of Pharmacy, UST

ABSTRACT

Sublimation is a change directly from the solid to the gaseous state without becoming liquid. In this experiment, we used the process of sublimation to purify the impure benzoic acid. We obtained from 5.00 g to 2.30 g of the sublimate compound. After we purify the acid we collected the pure and sublimate benzoic acid into two different capillary tubes. The two was then subjected to melting point through oil bath. Melting point is the temperature at which a given solid will melt. The oil bath was preferred because it is able to measure temperature even higher than 100 °C and are highly recommendable for compounds which have higher boiling points. As it was seen in the results, the sublimate had an initial temperature of 118 °C and stopped melting at 123 °C while the pure benzoic acid started from the initial temperature of 115 °C and stopped melting at 120 °C. This indicated that the pure benzoic acid has a higher vapour pressure than sublimate. The percentage recovery was computed and had a low percentage of 46%.

INTRODUCTION Sublimation is a technique used to purify solid mixtures. [1] We used this process to purify the compound of impure benzoic acid. The impurities in the benzoic acid have amino compounds that are present in a larger extent and must be removed because of phenyl and benzyl compounds that seriously affect the product. [2] This process occurs if the vapour pressure of the substances greater than the atmospheric pressure at the melting point. [3] The process of purification can be done only if the impurities are non-volatile or have significantly lower vapour pressure than the pure compound. The objective of this experiment are: [1] To purify the impure benzoic acid through sublimation. [2] To calculate the percentage recovery of benzoic acid after sublimation. [3] To identify the melting points of pure and sublimate benzoic acid through oil bath.

EXPERIMENTAL A. Compounds tested (or Samples used) The sample used in the experiment was a 5.00g of impure benzoic acid, its 2.30g of sublimate and pure. Oil used for determining the melting point temperatures of the compound. B. Procedure 1. Sublimation Sublimation was used to purify impure benzoic acid. We used a 5.00 g of impure benzoic acid and put it into a evaporating dish covered in filter paper with holes in it which is sealed with a masking tape. Before putting the evaporating dish on the hot plate we placed a tissue paper in top of it and continuously moistened 10-15 until most of the sample has vaporized. After the sample has been completely vaporized we collected the sublimate in the fume hood and weighed the sublimate for the percentage recovery.

2. Melting Point Determination The 2.30g of sublimate collected was ground with mortar and pestle. The sublimate’s powder was packed into 3-5 mm capillary tube and the pure benzoic powder in a separate tube. We prepared a iron stand and oil in a beaker for the oil bath. The capillary tubes were attached to the thermometer with a thread, rubber band, or copper wire. It was dipped into the heating oil bath. It was stirred constantly by a copper wire and until the compounds are completely method at a specific temperature.

RESULTS AND DISCUSSION Sublimation was the process used in the experiment. Impure benzoic acid in the evaporating dish was heated in the hot plate until the compound is form like a crystal like needle which is called sublimate. It is noticed that the benzoic acid did not pass through the liquid phase and went directly into the vapour phase. The sublimate was pre-weighed in a watch glass using a triple-beam balance. The sublimate was grounded using mortal and pestle. The powder was packed in a capillary tube and pure benzoic acid in a separate tube. The collected compound was used in determining the melting point of its temperature using oil bath. Figure 1. Sublimation set-up

The melting point determination in this experiment was done through the oil bath. The oil bath is highly recommendable for this experiment because of its temperature regulator. It operates the same principle as water bath but oil has generally far higher boiling point than water and can be used to provide temperature greater than 100 °C.

Figure 2. Melting Point Determination set-up The melting point determination Melting point is the temperature at which matter, mainly solids, change their states from solid to liquid. The melting point of a solid is affected by standard atmospheric pressure. Melting point takes place when the bonds holding the solid particles are weaken by heat.

Table 1. Data Weight of the impure benzoic acid | 5.00 g | Weight of the watch glass + sublimate | 93.90 g | Weight of watch glass (empty) | 91.60 g | Weight of the sublimate | 2.30 g | Percentage Recovery | 46% | Melting Point of the pure benzoic acid | 115 °C -120 °C | Melting Point of the sublimate | 118 °C – 123 °C |

Through the data obtained from the experiment, it showed how sublimation affected the weight of the impure benzoic acid until it be came a sublimate. The change in weight (from 5.00 g to 2.30 g) showed the turning point of the where in the impure benzoic acid is to its gaseous state. The pure benzoic acid has a high vapour pressure which made it melt in a higher temperature rather than the sublimate. It has a smaller dipole moment meaning the higher vapour pressure due to lower electrostatic attractive forces in the form of crystals.

REFERENCES
[1] Bayquen, A., Cruz, C., de Guia, R., Lampa, F., Pena, G., Sarile, A., Torres, P. (2009). Laboratory Manual in Organic Chemistry. 839, EDSA, South Triangle, Quezon City.: C & E Publishing, Inc.
[2] University of Colorado at Boulder, Department of Chemistry and Biochemistry. (2013). CU Boulder organic chemistry undergraduate courses lab techniques. Retrieved July 28, 2013. http://orgchem.colorado.edu/Technique/Procedures/Meltingpt/Meltingpt.html [3] Mangahas, M., Matute, C., Millares, E., (2010). Experiment #3. Sublimation and Melting Point determination. Retrieved July 28, 2013.http://www.scribd.com/doc/65633413/Experiment-3-Sublimation-and-Melting-Point-Determination…...

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