The purpose of this lab was to learn how to accurately determine melting points and to use this technique to then determine the melting points of two unkowns. The melting point is a physical property of a solid which can be used to help identify a substance. Usually, a solid will not melt at a specific temperature but instead will melt over a range. When using a melting point range, a narrow range suggests that the compound is relatively pure, whereas a larger range suggests a relative impurity. For this lab, a range of 2 degrees celsius was considered narrow and pure, with any greater range resulting in a retest with a new sample.
In this lab, the melting points of two unkowns and the three compounds naphthalene, urea and sulfanilamide were to be determined. By using the melting temperature device it was possible to quickly heat the known compounds to 10 degrees celsius below their given melting point range. From there, the heat could ramp up at about 1 degree celsius per minute so that the melting could be observed when it started and when it finished, thus providing a range.
The observed melting range for naphthalene was 81-83. The narrow range suggests a level of purity for the sample. The expected range was 79-80. The observed result was slightly higher than the given melting point range , but this could stem from the mel-Temp device thermometer being slightly off, or due to the purity of the sample. The observed melting range for urea was 133-135. Again, the narrow 2 degree range suggests the purity of the substance tested. However, here too the observed melting temperature range was slightly different than the given 132-134 range. Here, the difference is by 1 degree and does not suggest any larger error at play. The temperature range difference was slight and could be applicable to the thermometer device. The last given compound was sulfanilamide and it had an observed melting point range fo 165-167. This is the same range that was given for the known compound and fits within the 2 degree temperature range, suggesting that it is relatively pure.
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