Mixed Melting Points

I. LIQUID - Identification of an Unknown Liquid: Using the physical properties of Solubility, Density, and Boiling Point.

After each of the solids were completely dry, each was placed into a MelTemp device. The temperature at which each solid began to melt and completed melting was recorded.

During recrystallization, the solution was to be cooled to room temperature before placing it in an ice bath. Doing this allows enough time for the crystals to be formed because as the temperature decreases, the rate of crystallization slows down. If the solution was placed in the ice bath too quickly, then the cold would have blocked out the impurities and trapped them in the solution. The more impurities present, the lower the melting point so data would have been inaccurate. Also, if the melting point apparatus wasn’t set up correctly, the data would have been imprecise.

The mixture was transferred to an ice bath to crystallize the product, after which the product was collected by vacuum filtration on a Hirsch funnel, washing the flask with small aliquots of cold xylene and pouring the solution over the crystals, allowing the vacuum to thoroughly dry the product. Additional drying was achieved by transferring the product to filter paper and pressing the crystals to remove any excess moisture. The product was then weighed and a melting point determined. A comparative TLC was run in Hexanes:Ethyl Acetate solvent against maleic anhydride to verify the purity of the

These were most likely impurities, in which case I added a bit more water than was necessary. Also, the lab manual says to take two samples of each mixture (unknown; ½ phenacetin; ½ acetanilide) for the melting point, but we only conducted one.

In determining the melting point range of the aspirin, a capillary tube (sealed at one end) was one-third-filled with the dried aspirin. The capillary tube and a thermometer were immersed in an oil bath. The temperature at which the solid started to melt and the temperature when the entire sample was completely liquefied were recorded as the melting point temperature range.

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.

In order to fulfil the labs purpose, the lab was split into two parts. The first part consisted of measuring and determining the freezing point depression of the solution water. The second part consisted of measuring and determining the freezing point depression of a solution that consisted of water and an unknown solute.

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

Though the products had dissimilar melting point values, it is not enough to conclude that they are different. To be certain of the identity of the products, Infrared Spectroscopy (IR) and H- NMR were used. While IR is used to determine the functional groups present in an unknown substance through identification of covalent bonds, H-NMR is used to determine the structure of an unknown compound. The IR from both products had peaks at almost identical frequencies. The IR of both

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

Melting range would be closely related to a mixed sample whose constituents are most identical. In other words, melting point will have a wide range and would be below 200°C and above 95°C.

The purpose of this experiment is to identify an unknown substance by measuring the density and boiling point. I will be able to conclude which substance is my own from a list of known options stating what its real boiling point and density is.

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