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When determining the melting point of your pure benzophenone, some of the molten material had solidified...

When determining the melting point of your pure benzophenone, some of the molten material had solidified high on the thermometer and wire stirrer. How would your calculated value for the molecular weight of your unknown been affected (high, low, no effect) if this benzophenone failed melt and was not a part of the final mixture in the tube?
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Answer #1

When the molecular weight of the unknown(mixture of pure substance and impurity) is determined, the melting point depends on amount of impurity present.

The freezing or melting point depression is directly proportional to the molality of the substance dissolved.
Or the molecular weight calculated using the melting point is directly proportional to mass of substance present.
During determination of M. pt of the unknown, if some of the benzophenone sticks to the thermometer and stirrer, the molality of the impurity increases. As a result the calculated molecular weight will be high.
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