Evaluting Melting Point Determination
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1. In a mixture of approximately 20% camphor and 80% naphthalene. What would you expect the melting point to be? (+/-)camphor (175-177 Celsius) and naphthalene (80-81 Celsius).
2. Describe the expected type of error in the observed m.p. (unaffected, high, low and/or broad) when the melting point is determined as follows:
a. A melting temperature is used and the rate of heating is 15 Celsius/min.
b. An excessively large sample size is introduced into the capillary tube before using the melting temperature.
3. Decide whether the statement is always true. If not, explain when the statement would not be true.
a. An impurity always lowers the melting point of an organic compound.
b. A sharp melting point for an organic substance always indicates a single pure compound.
c. If mixing a sample of compound A with compound X gives a lower melting point than compound X alone, then X and A cannot be identical.
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This solution is comprised of a detailed response which will provide a student with a good understanding of all the chemistry questions being asked. Reasoning to further shed insight on the response given supplements the answers.
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For these questions, there may be an overall equation modelling the system (which would have been given to you), but for the most part, these systems all obey the same principles. The phenomenon is described as a mixed melting point, where a compound has an "impurity" and the melting temperature is decreased and the range is broadened greatly.
For you first question, you have naphthalene with camphor as the impurity. The melting temperature observed should be ...
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