Straightforward Questions Answered in the Powerpoint Slides Reaction: Heating th

Question

Straightforward Questions Answered in the Powerpoint Slides Reaction: Heating the starting materials under reflux What does it mean to heat under reflux? Why do we choose water as the reflux solvent? What are boiling chips used for? Why do we put a condenser on top of the reaction? Why do we add heat and let the reaction stir for 30 minutes? Why do we add sulfuric acid to the reaction after it cools as opposed to when it's still hot? Separation: Filtration of precipitate Why don't we do an aqueous and organic extraction in the separatory funnel? Why do you rinse the salicylic acid on the filter with ice cold water? Purification: Recrystallization of Salicylie Acid (no hot filtration needed) What is the difference in the amount of room temperature water vs. boiling water needed to dissolve the salicylic acid (assume a 1.2 gram yield of salicylic acid)? Remember, in the lab if you need x ml. of boiling water to dissolve a solid, then you should add a little more (definitely no more than 1.5 times the theoretical amount) to ensure it doesn't recrystallize prematurely Analysis: Melting point of Salicylic Acid What can you conclude if the melting point of the salicylic acid you just synthesized is 152-155°C and the 1:1 mix of your product and "synthetic" salicylic acid is 151-154°C?

Explanation / Answer

* Reflux: Boiling the reaction mixture over the boiling point temperature of solvent.

We choose water as a reflux solvent:

a) As the reaction components are dissolved in water

b) water has high boiling point , so the reflux will be at high temperature at which the reaction will get the sufficient energy to proceed

* Boilining chips are used to avoid sudden bumping of reflux solvent

* Cold water is passed through condenser which converts the solvent vapor (that evaporates out from the reaction system and goes up) to liquid.

* Heat is added to reflux the solvent and time is needed to complete the reaction.

* Addition of sulfuric acid is an exothermic process that generates a huge amount of heat. If we add it in hot condition , then there is a possibility of explosion.

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