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Author: Subject: Best way to heat a round bottom flask with a hotplate stirrer
zeropoint
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[*] posted on 31-10-2011 at 20:24
Best way to heat a round bottom flask with a hotplate stirrer


I'm a brand new chemistry hobbyist with newly acquired glassware and amateur lab equipment...and I'd like some advice on the best way to effectively channel the heat from my hotplate stirrer (Scilogex MS-H-S) to a 500 to 2000 mL RBF (while ultimately retaining the stirrer functionality).

For my very first experiment, I attempted to distill a 70% ethanol solution into a more concentrated solution. I followed the instructions given by the book, "The Illustrated Guide to Home Chemistry Experiments" by Robert Bruce Thompson.

I bought an 4qt aluminum saucepan from Target (the smallest one they had), filled it up a quarter of the way with some water, and suspended a 1000 mL RBF with 200 mL of 70% Ethanol inside so it was dipping into the water about where the solution level inside was. Then I turned on my hotplate...and kept turning up the heat...but the heating took so long that I gave up figuring that the surface area of the pot and the water inside was too much for the small hotplate to overcome.

So I switched it out with a 1QT stainless steel saucepan that I had in the kitchen. This snugly fit the 1000 mL RBF and worked effectively at heating up the water and eventually the solution inside the suspended flask.

BUT...obviously, this stainless steel solution wouldn't be ideal if I wanted to use a magnetic stirbar (required by some future experiments I'd like to try). Is it simply a case of me finding the right sized 1QT or 2QT aluminum saucepan? Or can you suggest a more elegant and lab-specific item and/or technique?

Thanks in advance for your help and patience.
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fledarmus
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[*] posted on 1-11-2011 at 03:28


You might try a Corning Ware dish. They may be a little more flexible in size than the aluminum pot. Since you have the magnetic stirrer, it can be helpful to toss a paper clip in the water bath and keep the water stirring - it will heat more uniformly that way, and transfer heat faster from the hot plate surface to the round bottom.

The lab solution (at least the one I use) is crystallizing dishes with silicon oil. Crystallizing dishes are thin round pyrex dishes with flat bottoms and relatively short sides Crystallizing Dishes It doesn't hurt to wrap some electrical tape around the sides to keep the glass in place if you break it. If I need a higher temperature solution, I switch to sand instead of silicon oil.

Good luck!

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hissingnoise
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[*] posted on 1-11-2011 at 03:43


Quote:
You might try a Corning Ware dish.

Aluminium is waaay better than heavy glass cookware for heat conduction!

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Steve_hi
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[*] posted on 1-11-2011 at 06:28


I started learning chemistry this year from the same book as you
I found that my hot plate stirrer is slow to heat as well so I used a cheap one from wallmart when I heat more than a 500ml flask.
I use Olive oil it has a high boiling point of 400°f and is a lot cheaper than silicon oil which boils at 500°f you can use a coffee can cut to about 4"filled with sand which works well too.
If you havent done so mr thompson also has a forrum you can join and he usully answers questions too.

http://forums.homesciencelab.com/
Good luck and have fun
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mr.crow
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[*] posted on 1-11-2011 at 06:55


Try to find a heating mantle. I have one for my 2L flask and absolutely love it! Make a controller out of a dimmer switch

Dr.Bob may have some mantles or dishes left. Highly recommended. Don't use non-laboratory glassware.

Also try canola oil, it can get to a higher temperature than olive oil and wont smoke




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Arthur Dent
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[*] posted on 1-11-2011 at 09:14


Hello Zeropoint. Welcome to the forum.

Your saucepan is a good idea. Don't worry, it doesn't affect the usage of a stirbar, the magnet in your hotplate is strong enough to go througn the saucepan easily. But instead of using water (evaporates) or oil (danger of ignition), use some plain old sand. it will fit your rbf, and will conduct heat very well, albeit slowly.

Use very clean sand (for sanblasting) but if you use beach sand make sure it is thoroughly washed, then cooked in the oven to eliminate all traces of organics (and the pungent smoke they emit).

You can also use stainless steel salad bowl from the dollar store, they are best suited for that purpose.

Robert






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zeropoint
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[*] posted on 1-11-2011 at 10:23


Thanks for all your replies! I'll soon let you know how I proceeded...and what resulted. Cheers!

A question in the meantime:

Where is the best place to get pure sand? A hardware store? How's this reptile sand I found on Amazon:
http://www.amazon.com/Zoo-Med-ReptiSand%C2%AE-Pounds-Desert/...



[Edited on 1-11-2011 by zeropoint]
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watson.fawkes
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[*] posted on 1-11-2011 at 16:19


Quote: Originally posted by zeropoint  
Where is the best place to get pure sand? A hardware store?
Hardware store, like a big box retailer. Out in the section with the concrete. Get the children's play sand. It's more rounded, less sharp.
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madscientist
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[*] posted on 12-11-2011 at 22:42


http://www.labdepotinc.com/Product_Details~id~440~pid~59986....

I would get something like this - a "round bottom flask adapter," also called a "reaction block." Cleaner and much safer than using an oil bath. Imagine what would happen if your round bottom flask cracked while full of something with a higher density and a lower boiling point than your oil (such as water). The liquid would dump to the bottom of the bath and boil explosively, spraying hot oil everywhere - a lot like a grease fire, minus the fire. A member of this site had this happen and was permanently disfigured by it. Scary stuff.

http://www.scilogex.com/scilogex-quarter-flask-reaction-bloc...

[Edited on 13-11-2011 by madscientist]




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dann2
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[*] posted on 13-11-2011 at 08:04



You can obtain Al beads. They are used for cooking blank pastry molds.
A few handfuls of them in a sauspan may be better that the sand. A half way house between the sand and the actual molded Al adapter!

[Edited on 13-11-2011 by dann2]
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