Question

Pre-lab questions for a Saponification lab:

A student assembled the reflex apparatus. Later the joint was seized and the RBF had to be broken to disassemble the apparatus. What was the cause of this? How could it have been prevented?

Filtering the soap using a washcloth exposes your hands to a very basc solution. What should you be doing to protect your hands from basic hydrolysis?

Thank you!

Answer 1

In a reflex apparatus, the round bottom flask (RBF) is connected to the condensor via the ground glass joints which at times tend to freeze/seize under different reaction conditions such as vaccum, strong bases, heating etc. A thin layer of grease or PTFE should be applied to the ground joints of the RBF and the condensor to prevent seizing. In this particular case, three scenarios exist for seizing of the joints a. if the grease was applied then it was leached due to the organic solvents, b. the strong base used in the saponification reaction attacked the glass joints and c. the heated sealed assembly was allowed to cool creating a pressure gradient that led to the seizing. The glass seizing can be prevented if the above points are taken care of.

To prevent your hands from the corrosive action of the basic solution, one should use latex or nitrile hand gloves while handling such solutions.