When experimentally finding a boiling point?

Question

is it the temperature that the liquid firsts starts to boil rapidly or is it once the temperature has leveled out? i am trying to determine what an unknown is in a lab and my sample will start to boil rapidly at around 114 degrees C, but the temp will continue increasing until about 147 degrees C, which is the boiling point?

Answer 1

Phase changes (i.e. boiling - liquid to vapor) occur at a "constant" temperature.  We say constant, but it may vary as much as 2 Celsius degrees between when it starts boiling and when it stops, but in between there is a period of time where the temperature doesn't change much at all.  The center of that plateau (where it levels out) is the boiling point.