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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: kellykell on February 25, 2009, 08:48:59 AM

Title: heating under reflux
Post by: kellykell on February 25, 2009, 08:48:59 AM

why should you never place a stopper in the top of the condenser when heating under reflux?

Title: Re: heating under reflux
Post by: nj_bartel on February 25, 2009, 09:01:20 AM

What happens when you heat something?

Title: Re: heating under reflux
Post by: kellykell on February 25, 2009, 09:02:28 AM

evaporation

Title: Re: heating under reflux
Post by: P on February 25, 2009, 09:18:37 AM

Yep - so the liquid turns to gas.  So why not stopper?

Title: Re: heating under reflux
Post by: kellykell on February 25, 2009, 10:30:00 AM

what do you mean? when dealing with organic compounds the reason why you heat under reflux is because the reactions are very slow and you want to heat for long periods of time without having evaporation losses, so why not use a stopper?

Title: Re: heating under reflux
Post by: ARGOS++ on February 25, 2009, 10:37:40 AM

Dear kellykell;

Think about the pressure if you heat a closed system.
And if you use a stopper then you have created a closed system.
Even more worst, if you will have a little decomposition during heating too.

Good Luck!
                    ARGOS⁺⁺

Title: Re: heating under reflux
Post by: P on February 25, 2009, 11:50:44 AM

Yea - ARGOS++ is right Kelly.  You wont loose any of the evapourated stock because it will turn back to liquid again in the condenser  -  however the pressure will build with a stoper in the flask and it will probably 'pop' out of the top.