Astudent carried out a simple distillation on a compound known to boil at 124 oc and they reported a boiling point of 116-117 o analysis of the compound showed it was pure and calibration of the thermometer indicated that it was accurate. what procedural error might the student have made in setting up the distillation?

Answer :

The correct answer is due to incorrect position of thermometer .

Distillation  is process of separating two volatile liquids on the basis of their boiling points .In involves the following set up ( shown in image )

Since the Boiling point is found   is 116-117 C which is near to 124 C , also the purity was checked and thermometer was calibrated .

So the only error could be possible is position of thermometer .

The position of  bulb of thermometer is very important to get an accurate reading of boiling point .The vapor so formed should touch the side walls of bulb as soon as they are formed .

May be  the bulb of thermometer was   kept far from the vapors formed by liquid so,  some of  the vapor before reaching to  bulb start condensing and their Temperature decreases .  

Hence , the  temperature shown by thermometer was decrease than actual boiling point  due to incorrect position of thermometer.