SUBLIMATION AND MELTING POINT DETERMINATION OF BENZOIC ACID University of Santo Tomas Faculty of Pharmacy; 2FPH Group 6
Pagaduan, Mikhaela; Pesito, Therese; Reyes, Thomas; Sarile, Criselda; Siapno; Yamilah; Simsuangco, Paul ABSTRACT
The aim of the past study was to evaluate the melting point of the product as well as to establish the relationship of the product collected with a standard. Five grams (5.00 g) of impure benzoic acid was heated and vaporized vaporized as the sublimate was collected thereafter. thereafter. The sublimate was weighed and the data was processed for a result of 24.00 % recovery of benzoic acid. To determine whether the sublimate was free from f rom impurities, the experiment then moved on to the melting point determination of the sublimate thr ough the capillary method. The collected sublimate as well as a sample of pure benzoic acid were packed in 2 capillary tubes and was then bounded with a thermometer and immersed in an oil bath until further changes in the physical state occurred. The recorded point of change of the impure benzoic acid started at 130.00 °C and ended at 131.00 °C. On the other hand, the pure benzoic acid started at a later 131.00 °C and quickly ended at 131.50 °C. Upon deliberation, both of the tested samples were between the ranges of 1°C-2°C which makes the sublimate closer to being qualified as a pure substance. However the theoretical melting point of benzoic acid was 122.41 °C. Upon comparison, the data gathered were too far from the theoretical data, thus the product was determined to be impure. INTRODUCTION
Sublimation, in physics, conversion of a substance from the solid to the vapour state without its becoming liquid. An example is the vaporization of frozen carbon dioxide (dry ice) at ordinary atmospheric pressure and temperature. The phenomenon is the result of vapour [1] pressure and temperature relationships.
no temperature change. When all the solid has melted, additional heat will raise the temperature of the liquid. The melting temperature of crystalline solids is a characteristic figure and is used to identify pure compounds and elements. Most mixtures and amorphous solids melt over a [2] range of temperatures.
Melting point, temperature at which the solid and liquid forms of a pure substance can exist in equilibrium. As heat is applied to a solid, its temperature will increase until the melting point is reached. More heat then will convert the solid into i nto a liquid with
In this experiment, for the researchers to be able to hypothetically collect pure benzoic acid from the impure origin, the gathered sample was vaporized and recollected the sublimate. To test whether the sublimate was pure, the researchers took advantage
of the melting point and was then tested alongside with pure benzoic acid of equal quantity. If the data gathered would be between the ranges of 1 °C to 2 °C, the researchers would then reach the conclusion that the sublimate is pure or free of any contamination. Otherwise, it would then be concluded that it remained to be impure due to its properties being inconsistent with the standard substance. At end of the experiment, the researchers were able to grasp the following objectives: (a) Collect benzoic acid from impure origin through sublimation. (b) Evaluate the percentage recovery of the collected sublimate. (c) Deliberate whether the sublimate still retained impure properties or not by evaluating its melting point with a pure sample of benzoic acid. EXPERIMENTAL
The experiment began with the setup in order to vaporize benzoic acid from the impure origin. The materials and instruments used for this phase of the experiment were: hot plate, evaporating dish, perforated filter paper, watch glass (inverted; where the sublimate will be gathered), masking tape (to temporarily seal the watch glass and evaporating dish together), and moistened tissue. Figure 1 shows the setup for this phase of the experiment.
Five grams (5.00 g) of impure benzoic acid was deposited in the evaporating dish, following a layer of perforated filter paper, and then a watch glass on top of the evaporating dish and then sealed with masking tape so as no vapor from benzoic acid would escape. A layer of moist tissue paper was applied on top of the watch glass to cool down the vapors of benzoic acid and quickly change its state as the sublimate on the watch glass. The setup stood for a length of 10-15 minutes at above 250.00 °C until most of the sample of impure benzoic acid was vaporized on the hot plate. After which, the setup was cooled and the sublimate was collected and weighed from the watch glass. Through the sublimate’s computed weight, the researchers also computed the sublimate’s percentage of recovery and was then recorded. On the next phase of the experiment, it had a different setup for the capillary method of determining the melting point. The capillary method, see Figure 2 for setup, called for the following materials: 2 capillary tubes (to store the samples), thermometer (to measure the melting point, an oil bath setup where the samples were heated upon.
5.00 g thus as calculated:
The resulting percentage of recovery of benzoic acid was 24.00 %. See Table 1 for the results of the first phase of the experiment (sublimation). The sublimate of the impure benzoic acid and pure benzoic acid were each grinded and packed in a slightly modified capillary tube with a sealed end. The capillary tubes, along with the thermometer were immersed into the oil bath and it was observed as its temperature gradually rose above 100.00 °C, which makes the oil bath a lot more convenient in this experiment than water bath due to its higher heat capacity. RESULT AND DISCUSSION
In the first phase, after subjecting the sample of benzoic acid of impure origin to vaporization, the heat changed the state of benzoic acid into a gaseous state. As it gradually accumulated through the perforated filter paper and started to solidify on the watch glass due to the moist tissue paper which serves as the cooling material which lowers the temperature of the substances in sequential contact with it. The researchers were able to collect 1.20 g of sublimate from the original sample of
After which, the crystals were grinded and packed in the capillary tube bounded on the thermometer. It was subjected to heat and the recorded results for the melting point of the samples. The assumed pure sample exhibited an average melting point of approximately 1 °C higher than the melting point of the sublimate. However the melting point was observed to be too far from the theoretical melting point of benzoic acid which is 122.41 °C, thus the experiment was deliberated that it remained to be impure. See table 2 for the results and observations for the melting point. Weight of impure 5.00 g benzoic acid Weight of empty 52.00 g watch glass Weight of watch 53.20 g glass + sublimate Weight of 1.20 g sublimate Percentage 24.00 % Recovery TABLE 1. Data and results collected processed from sublimation Initial melting
Final melting
temperature temperature 130.00 °C 131.00 °C
Sublimate of benzoic acid Pure 131.00 °C 131.50 °C benzoic acid (standard) TABLE 2. RECORDED RESULTS FOR THE INITIAL AND FINAL MELTING TEMPERATURE CONCLUSION
From the final results, it could be said that there had been an error that affected the [4] reliability of the final product . It was unusual for the pure sample of benzoic acid to exhibit a melting point too high, way higher than the original theoretical value. In conclusion the possible errors that were involved were: random error, due to environmental factors that slightly influenced the temperature upon the time recorded; or measurement error due to the device (thermometer) slope of reliability in the empirical results. REFERENCES
[1] sublimation. (2014). Retrieved September 10, 2014. In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/top ic/570767/sublimation [2] melting point. (2014). Retrieved September 10, 2014. In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/top ic/374185/melting-point [3] melting point determination. (2014). Retrieved September 10, 2014. Retrieved from
http://www.chem.wisc.edu/courses/342/Fa ll2004/Melting_Point.pdf [4] validity and reliability. (2014). Retrieved September 11, 2014. Retrieved from http://www.soc.iastate.edu/sapp/soc302rel val.html
