Classification Tests for Organic Halides

Earl Christian Mantes, Vicente Martires III, Jaira Lyn *Mauhay, Marlon Mejia, & GRalz Olasiman Abstract Benzoic acid is a naturally occurring and synthetically produced substance. The experiment aimed to determine and compare the melting point of the product with a standard. Five grams of impure benzoic acid was vaporized. Its sublimate was collected and weighed. Percentage recovery for the benzoic acid was obtained which is 14.536%. For the melting point determination, the sublimate was grind into a fine powder and a capillary tube was pressed into it. Also, pure benzoic acid was pressed by the tube for comparison. The two capillary tubes together with a thermometer was immersed in an oil bath and heated. Moreover, the initial and final temperatures for the substance were noted. The pure benzoic acid started to melt at 120C and was fully melted at 123C; the sublimate of the impure benzoic acid started to melt at 121C and was fully melted at 125C.

The experiment aimed to differentiate S

Introduction
Benzoic acid is a white and crystalline organic compound that has a melting point of 122C and a boiling point at 247 C. Benzoic acid in its crude form is called impure benzoic acid. The vapor pressure of a solid varies with its temperature. When matter undergoes a phase transition directly from a solid to gaseous form, or vapor, without passing through the more common liquid phase between the two, this term is called sublimation [1]. It is influenced by the pressure within the vessel, and is generally carried on under atmospheric pressure only. The process is employed as a means of purification of certain substances, which are heated in closed pans or retorts [2]. Moreover, melting point determination was employed together with sublimation to ascertain the identity and purity of an unknown compound. Melting point is defined as the temperature at which its solid and liquid phases coexist in equilibrium. The normal melting point of a substance is its melting point at one atmosphere pressure. Changes in pressure have very small effects on melting points, but they have large effects on boiling points [3]. In the experiment, capillary melting points in an oil bath were used. The thermometer and sample must be at the same temperature while the sample melts so the rate of heating must be slow as the melting point is approached

(about 1 degree per minute). Otherwise, the temperature of the thermometer bulb and the temperature of the crystals in the capillary may [4] not be the same . The experiment aims to purify the benzoic acid by sublimation, to determine and compare the melting point of the product with a standard, and calculate the percentage recovery of the impure benzoic acid.

Methodology
The materials needed were gathered. These were the bunsen burner, hard glass test tube, watch glass, evaporating dish, thermometer, iron stand, clamp, capillary tubes, rubber band, cooking oil, and benzoic acid. After this, the sublimation set-up was prepared. Five grams of impure benzoic acid was placed in an evaporating dish covered by a perforated filter paper. On top of it, pre-weighed watch glass was placed. It was secured tightly so no vapor can be released. A moistened tissue paper was put at the center top of the watch glass to help it cool. The set-up was heated using a hot plate.

Fig. No. 1 Sublimation Set- Up It was heated for almost ten minutes, until most of the sample has vaporized and crystals were produced. The collection of the sublimate was done on a fume hood because of the unwanted odor it released. The pre- weighed watch glass was inverted where the sublimate (including crystals adhering to the perforated filter paper) was collected and it was weighed. Afterwards, the percentage recovery was calculated. Meanwhile, for the melting point determination, the sublimate was grinded into a fine powder and the open end of a capillary tube was pressed into it. Also, a capillary tube was pressed in the pure benzoic acid for comparison. The two capillary tubes were attached to a thermometer using a rubber band. The closed ends of the tubes are aligned with the mercury bulb of the thermometer. It was immersed in an oil bath and heated. The initial temperature at which the sublimate starts to melt and the final temperature at which it is completely melted were noted and compared.

Results
Data Obtained Table No. 1 Data obtained from the experiment Weight of impure benzoic acid 5.00 g. Weight of watch glass + sublimate Weight of watch glass (empty) Weight of sublimate 52.1543 g. 51.4275 g. 0.7268 g.

Table No. 1 illustrates that 5.00 g of impure benzoic acid was used in the experiment and the weight of the sublimate collected was 0.7268 g. Table No. 2. The Initial and Final Temperature of the Pure Benzoic Acid and the Sublimate Tinitial Tfinal Pure benzoic acid 120C 123C Sublimate 121C 125C Table No. 1 shows that pure benzoic started to melt at 120C and was completely melted at 123C. Conversely, the sublimate of the impure benzoic acid started to melt at 121C and was completely melted at 125C. Calculation: Percentage recovery: weight of sublimate x 100 weight of impure benzoic acid = 0.7268 g x 100 5.00 g = 14.536% The calculation tells that the group ended up with 14.536% of the original substance which is the impure benzoic acid.

Discussion
Fig. No. 2 Melting Point Set-up for the Capillary Tube and Thermometer (the set-up will be completed by the Bunsen burner and iron stand) After performing the sublimation procedure, the impure benzoic acid was vaporized and purified. The sublimate was weighed at 0.7268 g. Recovery of the benzoic acid was computed at 14.536% by dividing the weight of the sublimate by the weight of the

impure benzoic acid, and then multiplied to 100. This means that there was 14.536% retrieved within the original substance. The immersion of the impure and pure benzoic acid to an oil bath determined the melting point of the sample. Oil bath was used because it does not evaporate and does not need to be refilled all the time, unlike the water bath. Also, oil can be heated to much higher temperatures without boiling it especially in experiments needing temperature greater than 100C. The pure benzoic acid started melting at 120C and was completely melted at 123C while the sublimate of the impure benzoic acid started melting at 121C and was completely melted at 125C. The greater the range, the more impurities present. A range of less than 2C indicates a pure substance. A pure substance has a xed melting point while an impure substance melts over a wide range of temperatures and at a lower temperature than the pure substance. The melting points of almost all substances are available in tables. If both are pure benzoic acid the melting point will remain the same but if the sample is not pure benzoic acid then the melting point will be lowered [5].

for the percentage recovery. This may be due to fewer crystals or sublimate collected within the process of sublimation. Longer time for the process to occur is needed so enough and more sublimate will be gathered. For the melting point determination, a range of 2C indicates a pure substance but the collected sublimate has a range of 4C. It shows that the sublimate is still not that pure but is close to being a pure benzoic acid. Factors that might affect the experiment included loss vapor due to poor sublimation set-up or inaccurate measurements of the substances.

References
[1] Jones, A. (2012). Sublimation. http://physics.about.com/od/glossary/g/su blimation.htm [2] Water Treatment Solutions. Sublimation. http://www.lenntech.com/chemistry/subli mation.htm [3] Whitten, K., Davis, R., Peck, M. L. and Stanley,G. (2010). Sublimation and the Vapor Pressure of Solids. Chemistry. 9th edition. USA:Brooks/Cole. [4] Melting Point Determination. http://www.chem.wisc.edu/courses/342/Fa ll2004/Melting_Point.pdf [5] Recyrstallization of Benzoic Acid and Determination of its Melting Point. Science and Technology in Action. 2nd edition. http://www.sciencetechnologyaction.com/l essons/2/26/GSK-lesson.pdf

Conclusion
The method of sublimation is very effective for purifying substances in small quantities because there is a very little loss of the material in the process. As seen in the results, the performed experiment yielded a lower result