A Brief Introduction to Refluxing

Professor Davis discusses the advantages and details of refluxing organic solutions in the laboratory.

[@lananhnguyen7415]

7 years later and your videos are still super educational. Thanks so much for the education you provided us. God bless you!

[@ChemSurvival]

thank you for the comment! Never stop studying :-)

[@sitakshigupta9624]

Short, concise and on-point !! Very well-explained.. please keep up the great work..!

[@ChemSurvival]

Thanks for the comments, folks. I will keep working to post useful videos. If there is another chemistry question burning in your brain, you can contact me through my ChemSurvival webpage to submit a request!

[@ChemSurvival]

I'm glad you liked the video. Don't forget to check out my other uploads on the channel and tell your friends!

[@ChemSurvival]

Hi Zachary. If you close the reflux condenser and heat the system, the pressure will not decrease... it will increase! The consequences can be catastrophic when the glassware fails or the stopper blows out and superheated solvent goes flying everywhere. It is possible to work in systems like this under reduced pressure with the proper precautions, but remember that lower applied pressure means lower boiling points, and usually the point of refluxing is to add heat.

[@ChemSurvival]

Thanks! I'm glad you like the videos!

[@sergioluna2048]

Great video and explanation. The visuals of the particles are extremely helpful to understanding the process.

[@ChemSurvival]

Good question, Mary. The answer will depend on the application, but on the scale you most often encounter in the research lab (hundreds of milliliters of solvent using 14/20 or 24/40 standard taper glassware) most reflux condensers are about a foot long. Anything so volatile that it can significantly traverse such a distance as vapor at the temperature of cold tap water is not likely to be a useful reaction solvent anyway!

[@neiritanuki2072]

Illustration speaks everything! Good job!

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Nice👍

[@AbujanDisco]

thank you it was insightful....keep making these if you can they are my replacement to the 50 pages of operations i have to read before the experiments hahaha.

[@isteakahamedimon]

Especially thanks for your last animation. At last, I got it.

[@ChemSurvival]

Awesome! 😀Glad it helped! Please remember to subscribe, check out my other videos and share with your classmates/friends!

[@RedJonathon719]

Brilliant video - was looking for a video since I couldn’t find any other half decent explanation for this.

[@user-br1xn5hw8h]

10 years later and still

[@soumyashree7729]

This was the best vdo i saw today ❤

[@joshitheyoshi2533]

Love your videos and animations. Makes everything so easy.

[@ChemSurvival]

Joshi The Yoshi humble thanks for the compliment. please pass the videos on!

[@joshitheyoshi2533]

ChemSurvival Definitely, your teaching really is exceptional- I'll make sure to do that after I finish orgo. No need to help other people ruin the curve in orgo lab while I'm taking it though.

[@mrstratau6513]

Excellent. Straight to the point.

[@ChemSurvival]

It is possible to direct any escaping vapor to a cold trap for collection, but in most cases this will not be worth the trouble. Most reaction solvents chosen for refluxing have boiling points well above room temperature, and the condenser is remarkably efficient at re-collecting the solvent in the original flask. I'm not sure I understand your comment about solvents boiling below zero C. Refluxing as shown here is typically employed with solvents which boil above room temp.

[@aniketkalta9752]

One of best video explained cool nd easy to grasp

[@mayasinsight9911]

Best demonstration .. I am through this 👍

[@ChemSurvival]

Glad it helped!!! Please share it with your classmates :-)

[@YarinSA111]

The hole below connects to the water. And where does the second hole connect?

[@shaneoriordan8988]

Doing exams tomorrow thanks for this !

[@AdriannesWorld]

Great video for beginners Thank U.

[@ChemSurvival]

glad you found it helpful! Please enjoy some of the other videos and consider subscribing/sharing!

[@arabian306]

Thank you Davis.You are the best!!!

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Just came across your video and really love it ... Subscribed🎉🎉🎉🥳

[@ChemSurvival]

thanks! more videos coming this fall!!!!

[@troyallen8223]

@@ChemSurvival Sweet. Till then will be checking out all of your other ones🥳

[@email_today]

what is the point of reflux? once the reactant has evaporated and then condensed back down again, aren't you back at square one again? what does reflux achieve that a simple distillation would not?

[@daviddavidson8869]

No, because it allows the reaction to continue on heat while containing the reactants in the vessel.

[@SpeedlPN]

Thank you Amber

[@jhyland87]

I was wondering the same thing for a while. When you get to something that requires you to boil something for an extended period of time, you'll quickly realize why it's important to reflux :-)

[@angeloafanador9798]

@@jhyland87 yup when you need to do something like this basically the way I told my kids anyway you have water that boils at 212 degrees Fahrenheit at sea level and you have something else that you want it boils of at 200 degrees Fahrenheit you want the stuff that evaporates faster so the cold finger is inside coiling the vapors the lower boiling point stays in the flask if the condenser is hooked up right and water inlet is at the cold temperature needed and water over some time will leave the flask then all you have left is what boils off at 200 degrees Fahrenheit. I could be wrong I'm just learning if I'm wrong please correct me thank you. my grammar is bad so are my nerves in my brain

[@otacon1024]

...dude, did you even watch the video? The first half of it directly answers your question.

[@Sneha-ij8rt]

i have o level day after tomorrow.This video helped me a lot

[@nutbreaker22]

Very good, right to the point information!

[@psyiam8726]

I really appreciate this video because it is so understandable !!!!

[@j3891]

amazing video!!!!!!! thanks

[@ChemSurvival]

Thanks for watching!

[@danssv8]

Very informative , thanks for posting :-)

[@ChemSurvival]

Thanks for watching, and especially for sharing! I'm glad it was helpful.

[@sunsunnews]

Thank you very much! Your video clip is very informative and useful. It helps me a lot.

[@MrInzombia]

such a great video

[@harithhazim8359]

Thank you very much!

[@tilen3870]

Hey, a question: is air-cooled condenser (where there is no liquid introduced to cool it - so basicly you mount it on a flask and it looks like a prolonged neck, where only ambient air cools it as you go "up") considered a reflux condenser? Thank you :)

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[@Marcosss-7-years-ago]

Very good explanations!

[@Rauchgestein]

I don't get what a "Thermowell" is. Is this just a brand for heating mantles? Or does the Thermowell controll the temperature?

[@moshibudikgaogelo9383]

Very brief, thank you

[@hameedhabeeblahi576]

short and well explained

[@bharathk9594]

Thanks for the video. The one thing I have trouble understanding is if the temperature is to be constant at the boiling temperature of the solvent or liquid, then won't condensing the liquid back into the flask cool the liquid. I assume the drip rate is small enough but from an energy balance standpoint you are removing heat from the vapor that is rising, so won't the temperature fluctuate each time the vapor condenses?

[@vvs7185]

It helped me a lot!!! :) Thanks from Bolivia! :D

[@ChemSurvival]

vania vargas silva A very humble "You're Welcome" from the USA! I'm so glad it helped you!

[@m35926]

So when my manual says to "Heat to reflux" that essentially means "Heat until you start seeing dripping coming from reflux condenser" because that means it's boiling. Is that right?

[@ChemSurvival]

+A Whether Moments Poet You got it. 'Heat to reflux for 30 minutes", for example, means get a nice boil going so that condensate is dripping back down into the flask, then start your timer. Thirty minutes later, remove the heat.

[@m35926]

ChemSurvival Awesome, thanks for your help. I just did the experiment and everything went really well. Thank you again!!

[@zacharyivanhawkins251]

Great video, at about 3:25 you mention that the reflux condenser is open and exposed to atmospheric pressure. If you were to put a stopper and/or thermometer at the top, what degree of vacuum (in psi, HG, or torr) would be present in the system? And what would be the circumstances or factors that influence that pressurized system? Is the level that the condenser and RBF in comparison to sea level a factor? I'm curious, cuz I know some lab exps. require vacuum pumps.

[@malcohaze]

How do you determined the length of condenser that is most effective? Obviously the amount of solvent is key. But when is it too much to where you start to lose vapor?

[@KimDianeH30]

Thanks for the video!

[@geetika9995]

Thanks for clearing my doubt 😘

[@DiLiNiTi]

great video, thanks!

[@ChemSurvival]

thanks for watching!

[@pivotbrawler86]

Your voice sounds very familiar, are you the same Professor Davis who teaches the chemistry course on great courses plus?

[@ChemSurvival]

Guilty as charged 😎

[@AlexanderShermanLapidaryus]

Hey, thanks for an informative video. But why need the stir plate? Does it depend on the chemicals? This guy refluxes without the stir plate. Reflux

[@ChemSurvival]

Hi Alexander. Having a rotating spinbar in the flask promotes even heating, which in turn reduces the risk of what chemists commonly call 'bumping' or flash boiling. In short, small, superheated pockets in the solvent can cause it to rapidly vaporize, foam up and shoot into (and sometimes beyond!) the condenser. Generally, once a reflux is humming along nicely this is no longer a significant risk. The technique can be performed without stirring if the solvent is of relatively low volatility or if the heat source can be quickly removed or decreased when/if flash boiling begins, but since I teach an introductory lab, I have included it for pedagogical reasons.

[@mrjollyguy25]

Thank you!

[@shivanikadirgamarajah7563]

Why is the condenser in a vertical position

[@UniChannel-pg8ol]

THIS IS AMAZING, AND GOD IS GOD!

[@someonec4342]

A have a question.. why we attach the water inlet tubing to the bottom connection and the water outlet tubing to the top connection and not opposite? Thank you

[@ChemSurvival]

This ensures that the jacket will fill completely with water, keeping all of the interior walls cool. If you plumbed it in reverse, you can get a situation in which just a trickle of water falls down one side of the condenser's jacket, reducing its cooling efficiency and possibly allowing solvent vapor to escape!

[@someonec4342]

@@ChemSurvival thank you very much for your quick answer!

[@troylenny5848]

Hello that's a pretty cool video. What software allows for such animations?

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[@robertostman2075]

I wonder how much silver, gold and other expensive stuff end up in the drain... lithium, heavy metals, phosphorus, nitrates... all these things that could be resicled straight from the drains... specially in a big city... if you want, I have a video in my patreon page where I explain how to make distillated water at home...

[@qweef69]

so is reflux a test run? it seems illogical to condense something back into its original flask. is this method used to purify a compound? what are the benefits for refluxing?

[@ChemSurvival]

kzbin.info/www/bejne/kGeyqoF4bbtqfsU I assume you are referring to fractional distillation in comparison? My video on fractional distillation will help to explain. Though fractional stills and reflux apparatus might look very similar, they are used for very different purposes! Refluxing is used to add heat to a system for an extended time without loss of volume. This might be done to accellerate a reaction or to encourage stubborn solutes to dissolve. It is a very versatile technique, but it is NOT a separation technique.

[@mikebrothers5689]

Like Ur easy to follow content

[@ChemSurvival]

Thanks! Glad to see these videos are still reaching students and fans of chemistry!

[@2kfanman23]

ChemSurvival Hi, first off, thanks for posting this. Very informative, and very easy to understand. One quick question, is the thermowell necessary, or can you do this without one? Also, if you do need one, can you link me to one that would work for this application? I've got everything else, but all I can find are tubular thermowells.

[@ChemSurvival]

Thanks for the kind words. Try searching VWR's website for 'Heating Mantle' That should get you where you need to be

[@2kfanman23]

Thank you. I'll work from there.

[@paragchaudhary38]

That was great 👍🏼

[@halbdaf4615]

how do we know when will the reaction finish?

[@freethebaseiliesse4126]

what can be done if the fumes are very dense in a reaction and despite the condensing apartus, a part of the fumes are escaping. is it possible to put an second condenser in line to increase the amount of condensing surface? i use to put an champagna glass with some water at the top to avoid to block completely the system whuiich when the pression increase is pusdhing a bit thge glas to release the pression, but i would like to avoid no loss of the fumes which are the most important in the reaction. does it exist sdpecial condenser which solve that ???? (sorry for my bad english, i speack normally french)

[@otacon1024]

Well, you need to increase the efficiency of condensation, which you can do in a number of different ways. One would be increasing the surface area by getting a longer column, using a specialized column (Vigreux, Snyder, Widmer for air-cooled; Allihn, Graham, Dimroth for liquid-cooled), or stacking multiple columns. You can also lower the temperature. For air-cooled, you could pack the outside with ice. For liquid-cooled, pump a cooler liquid, such as ice water vs regular. Useful reading: en.wikipedia.org/wiki/Condenser_(laboratory)

[@zblacky2031]

So basically just a liebig condenser?

[@ChemSurvival]

Basically yes. Liebigs are usually the simplest part available to get the job done, although the technique can be performed with condensers of varying designs, most notably Allihn and Dimroth condensers are also sometimes used when even more efficient condensation is needed

[@anewaqavakatoga987]

Why is the organic substance heated in the first place? If it wasn't heated, refluxing wouldn't be used, would it?

[@ChemSurvival]

You can be used for a number of reasons. Sometimes it's to accelerate reactions or even change the product that forms and other times to help dissolve stubborn solutes. But whatever the reason for using it, the technique of refluxing is all about adding heat without the risk of losing volume.

[@Zzznmop]

Is it possible to relieve the pressure by connecting a vacuum apparatus to the top? also allowing you to boil at lower temperatures and less chance for thermal degradation

[@ChemSurvival]

+zach p interesting question. I have never seen or heard of a 'vacuum reflux'. If you want to perform the temperature below a solvent's boiling point, just use a heating block to carefully control the temperature of the mixture. As for relieving pressure, there is no pressure build up during a reflux since the top of the apparatus is open to the atmosphere!

[@gwendolyn8425]

+ChemSurvival But he says he wants to connect the vacuum apparatus to the top, so it would no longer be open to the atmosphere.

[@ChemSurvival]

+Gabby Jerz I understand this. But think about what a vacuum pump does and what refluxing tries to achieve. A vacuum pump would suck a fair amount of the vapor out of the apparatus. Refluxing is all about recovering that vapor and keeping it in! To reduce the pressure in the system would mean actively pumping out the vapor that you are trying to save with the condenser. The two techniques are in conflict here. Temperature control of that level can be achieved far more easily simply by using a thermostated bath to do the heating to the desired temperature.

[@Zzznmop]

ChemSurvival cold trap for the win :)

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Better late than never... 2021...

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[@giscarddib7312]

is this video under Creative Commons CC?

[@ChemSurvival]

NO. This material is (C) - ChemSurvival Enterprises, LLC. However, if you are interested in reproducing some or all of it for instructional purposes, please contact me directly through my website www.chemsurvival.com and I will consider authorizing its royalty-free use depending on the intended use!

[@reshad404]

Amazing

[@reecefuller89]

Thanks that helped

[@shivanikadirgamarajah7563]

Why is the condenser used

[@noahfin5919]

Shivani Kadirgamarajah so the solvent goes back into the solution

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wonderful !

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Excellent explanation

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You can just use a balloon over a flask to accomplish the same results.

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[@ChemSurvival]

how can I help you?

[@shivanikadirgamarajah7563]

why is the condensor placed in a vertical position

[@shivanikadirgamarajah7563]

why is the condensor used

[@ChemSurvival]

The condenser is vertical so that condensing solvent will fall back into the boiling mixture. This allows for indefinite boiling of the mixture without loss of volume.

[@SolaScriptura49]

excellent video, thanks!

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[@ChemSurvival]

:-) Thanks! Please spread the word by subscribing to my channel and sharing my videos!