Functional Groups - Boiling Point
A simple, although not entirely accurate, definition for boiling point is the temperature at which a substance is readily converted from the liquid phase to the gas phase. The boiling point of a substance is determined by how strongly the molecules are attracted to each other. The larger the interaction between molecules, the higher the boiling point. The magnitude of the interactions are determined by two factors:
(1) the kind of molecule
molecules that contain carbonyl or hydroxyl groups (aldehydes, ketones and alcohols)* tend to attract each other to a greater extent than do molecules without these groups (alkanes, alkenes and alkynes).
(2) the size of the molecule
larger molecules tend to attract each other more readily than do smaller molecules.
The boiling point does a very good job of narrowing down the possible identity of an unknown compound. With a short list of possible compounds, like in this lab, the boiling point would do such a good job that you might be able to identify your compound without using any other information. To prevent this, you will only be given a range into which the boiling point of your compound falls. For example, if your unknown had a boiling point of 45 degrees Celsius, you might be told that the boiling point falls between 0 and 50 degrees.
* Many of the other functional groups only briefly mentioned in this experiment have the same effect on boiling point.