The Purity and Purification of Solids-Melting Point Essay

4- chlorobenzoic acid which was the aqueous layer has a theoretical melting point of 240-243°C, the organic layer, 4-chlorobenzyl alcohol has a theoretical melting point of 68-71°C. During our experiment we were unable to collect any data for the organic

No correction had to be made to the melting points because the standard melted in the range labeled on the bottle. The melted point observed is the correct melting point.

4. The melting points of the solids were tested by placing them in crucibles and heating them using a hot plate.

Maleic acid has a melting point of C and Fumaric acid has a melting point of C. The substance that has a higher melting

2. The least precise measurement was the temperature but more specifically the freezing points of the solutions and solutes. Due to the freezing point only having two significant figures, the data is limited to two significant figures as well.

We first, determined the percent recovery of both vanillin and unknown and then determined the melting range of both compounds. Determining the melting point range, verifies whether or not students purified the compounds properly. Pure compounds tend to have smaller and higher melting points than the original compound. Students worked individually when determining the melting range of vanillin—we were to determine the melting ranges of crude vanillin and the recrystallized vanillin made in the first lab. Moreover, students worked in pairs when determining the melting range of the unknown by using a commercial apparatus. For both solids, we watched the crystals melt. We recorded the temperature at which the solid first began melting and when the solid was completely

Melting Point Data Table Compound Aspirin Caffeine Salicylamide Actual MP (ºC) 93 - 98 260 - 262 96 - 102 Expected MP (ºC) 135 236 140 Percent Error (%) ~30% ~12% ~30%

I would have liked to do one more trial on each mixture for melting point analysis to confirm that my results were consistent. Furthermore, I would go back and repeat the second experiment to avoid adding HCl to the organic layer in order to separate an accurate weight of the unknown solid and ensure that the purity of the unknown is unaffected by an accidental HCl addition. I am unsure if my results are truly accurate due to the HCl addition and other errors, which means that the experiment would need to be repeated multiple times in order to report a consistent result. In conclusion, this experiment covered the techniques of recrystallization and melting point analysis, both of which are based on understanding physical properties such as water solubility and melting point.

Discussion: As seen in the melting point determination, the average melting point range of the product was 172.2-185.3ºC. The melting points of the possible products are listed as 101ºC for o-methoxybenzoic acid, 110ºC for m- methoxybenzoic acid, and 185ºC for p- methoxybenzoic acid. As the melting point of the sample

The melting points were 132.1C-136.4C (for urea), 132.1C-135.3C (for trans-cinnamic acid), and 99.2C-129.8C (for the 50-50 mixture). While observing the compounds in the apparatus, the 50-50 mixture melted at a lower temperature and rate as opposed to urea and the trans-cinnamic acid. Urea and trans-cinnamic acid held narrow ranges such as 4.3 and 3.2 while the 50-50 mixture held a wider range of 30.6. According to “Melting Points,” published by Kathleen Armstrong, “Melting points are sensitive to the purity of the organic compound, since the crystal lattice of the compound is disrupted by the presence of an impurity (2009). ”

The objectives of this lab are, as follows; to understand what occurs at the molecular level when a substance melts; to understand the primary purpose of melting point data; to demonstrate the technique for obtaining the melting point of an organic substance; and to explain the effect of impurities on the melting point of a substance. Through the experimentation of three substances, tetracosane, 1-tetradecanol and a mixture of the two, observations can be made in reference to melting point concerning polarity, molecular weight and purity of the substance. When comparing the two substances, it is evident that heavy molecule weight of tetracosane allowed

The beaker was slowly heated on a hot plate with low stirring until most of the stilbene was dissolved. 0.4 g of pyridinium tribromide was measured and added to the beaker after 5 minutes of heating. Small amounts of ethanol were used to clean the sides of the beaker. The beaker was heated for an additional 10 minutes on low temperature. An ice bath was prepared. The beaker was removed from the hot plate and left to cool to room temperature. Once at room temperature, the beaker was placed in the ice bath for 15 minutes. The solid product was collected through vacuum filtration and the product was weighed and a melting point was taken. Waste was disposed of in the correct waste bins and lab bench was cleaned

To apply thermal analysis to the two-component system, naphthalene-biphenyl at atmospheric temperature. The analysis will be represented by a solid-liquid phase diagram (freezing point diagram).

Brittain, C. G. (2009). Using Melting Point to Determine Purity of Crystalline Solids. Retrieved from http://www.chm.uri.edu/mmcgregor/chm228/use_of_melting_point_apparatus.pdf