Melting Point
The heat was lowered when the temperature reached within 10 degrees of the PM range. The voltage was kept an eye on so as to have the temperature increase by 1 degree every half minute. The first drop of naphthalene was seen at 78 degrees. The solid fully melted at 80 degrees Celsius. A separate Mel- Temp was used to avoid the cooling wait time and the process was repeated with Urea. The first drop of liquid appeared at 132, and the melting finished at 134. Yet again, the Sulfanilamide was tested and seen to show a range of 165-167 degrees for its melting point.
The same set up for the apparatus stated above was used with an unknown compound (#2). The compound was heated quickly in one Mel-Temp to 132, where it began to melt at a voltage reading of 4. Another, cooled Mel-Temp was used to narrow down the range of the melting point to 132 to 134. A mix of Naphthalene and the unknown compound was heated in the Mel- Temp to 132, where the first drop of liquid appeared. It finished melting at 134 degrees. The apparatus was turned off, including the voltage and digital thermometer.
The used capillaries were placed in the dish next to the equipment. Results Compound PM Range (Celsius) Naphthalene 78-80 urea 133-136 Sulfanilamide 164-166 Unknown #2 134-1 35 Impurities 132-134 Discussion For the first part Of the lab, the melting points Of the known compounds were accurate. The naphthalene should have been 79-800, the urea 132-1340, and the Sulfanilamide 165-1670. The experimental ranges were all within a degree or two of deviation from the expected values.
The identity of the unknown compound #2 appears to be Urea. The melting point range fit with the values pointed out in the literature, as well as the experimental. The impurity compound, however, wasn’t as low as expected. The melting point had only dropped two degrees, but the naphthalene should have significantly decreased the compounds melting point. This could have been a result of the lack of a consistent mixture. The level of naphthalene compared to the known (expected to be urea) could have been significantly lower.
Should there have been a greater presence of the former compound, the melting point would have been lower as expected. The reason for this is the impurities decrease the vapor pressure of the system, thereby decreasing the melting point. Some other common errors during testing could have been too rapid heating during the experiment. With proper care and patience, the range of the melting point could have been more accurate. Though, this wouldn’t have had a great effect on the results, as the digital thermometer had an accuracy within 2 degrees.
