The Purity and Purification of Solids-Melting Point

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Introduction: The method for purifying solids is done by observing the melting point. This is important because if there is an impure substance the melting point would be depression and the melting range would be broader. By finding the melting point of a known substance one can then observe an unknown substance’s melting point to see if the points are the same and try to figure out the unknown.

Experimental Section: The first known substance we used was Biphenyl. 68 degrees Celsius is the known melting point. We used the capillary method and observed the melting point using a Mel-temp device. The next substance whose melting point we observed was 90 % Naphthalene, 10 % Biphenyl. In the last part of the experiment I observed the melting point of Unknown E. After finding the melting point of Unknown E, I used 2-Chloroacetemide with a known melting point between 116-118 degrees Celsius and mixed it with Unknown E. I also took Acetanilide with a known melting point of 114.4 degrees Celsius and mixed it with Unknown E. I then observed these melting points to try and determine the identity of Unknown E.

Results:
Our first known was 100 % Biphenyl. We did three trials. The following table represents our results.
Melting Point (Celsius)Melting Point Range (Celsius)
Trial One64.6 60.3-64.6
Trial Two64.460.5-64.4
Trial Three66.059.6-66.0

Our second known was 90 % Biphenyl and 10 % Naphthalene. The following table represents out results.
Melting Point (Celsius)Melting Point Range (Celsius)
Trial One77.760.0-77.7
Trial Two78.263.8-78.2

This table represents the values that the class got while observing Biphenyl or Naphthalene melting points. 100 % Naphthalene (Degrees Celsius)100 % Biphenyl (Degrees Celsius) 83.6 66.9
80.269.7
82.870.2
81.569.7
81.664.6
81.664.4
81.166.0
80.666.3
81.266.2
66.5
68.8
68.2
66.3

This table represents the classes’ values when observing the melting points of...
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