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Author: Subject: Insufficient power for heater - stirrer ?
Heisenburger
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[*] posted on 17-2-2023 at 19:40
Insufficient power for heater - stirrer ?


Hello everyone, this is my first post on the forum.
I've got a bit of theoretical knowledge in general chemistry but not much practice, I'd like to have a bit of fun and learn more while doing it :D

So I'm getting a basic chemistry setup going and bought a magnetic heater - stirrer.
While the stirring works just fine the heating seems to be really low power or defective, because after 50 minutes I could not get 200 mL of water to boil.
It's supposed to be 180 Watts...

I should send it back right ? Or does that seem normal for this power output ?
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Sulaiman
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[*] posted on 17-2-2023 at 20:27


180W is good for keeping solutions warm or hot but not for boiling.

The heat loss from the hotplate and the beaker may be more than 180W at 100oC,
So thermal insulation may be required just to reach 100oC (eg aluminium foil)

The heat of vapourisation for water is 2257J/g
So if the hot plate and beaker are well insulated
(all of the heat goes to boiling)
180W could boill off 180/2257 g/s = 0.08 grammes/second,
That is more than 20 minutes to boil off 100 ml (1ml = 1g) of water.

So there is nothing wrong with your hotplate stirrer
it is just under powered for your requirements.

My favourite heaters are heating mantles, but they aren't cheap.

For several years my main heater was one of these
https://www.ebay.co.uk/itm/225427887170
A typical generic 1500w electric hotplate.
(after I finally killed it, I bought a cheap used dual hotplate)
It would be better with stirring but it was good enough for several years of experimenting, including distillations.

I've also used one of these for general use and distillations including sulphuric acid.
https://www.ebay.co.uk/itm/392312041053
A small butane cooker.

Many members recommend a Corning hotplate/stirrer
but too expensive for me.

PS. For test tube scale I use either a small spirit lamp or an Ikea tealight candle.

Welcome to science madness.

If in doubt about buying or using equipment or chemicals
do some research first then feel free to ask questions.
We all start out as noobs ;)

PPS your first equipment buy should be comfortable eye protection
Goggles or/and a face shield
use every time you do any practical chemistry.

Consider a lab coat or an apron or something equivalent
non-flammable, quickly and easily removed

Gloves are sometimes necessary, sometimes a hazard, but generally not required.
(real mad scientists have many types of gloves)


[Edited on 18-2-2023 by Sulaiman]




CAUTION : Hobby Chemist, not Professional or even Amateur
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Fery
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[*] posted on 17-2-2023 at 23:45


Quote: Originally posted by Sulaiman  
My favourite heaters are heating mantles, but they aren't cheap.

https://sklep-chemland.pl/en/urzadzenia-chemland/plaszcze-la...
https://sklep-chemland.pl/en/urzadzenia-chemland/plaszcze-la...
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Jeeves225
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[*] posted on 18-2-2023 at 02:55


I would agree that it is underpowered. I've used a hot plate stirrer by IKA before to boil solutions up to 1 L, and I see that that specific model is 1 kW. I probably wouldn't recommend anything below 750 W, or else you could wait a long time for it to get up to temperature.
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Tsjerk
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[*] posted on 18-2-2023 at 07:22


Yes, and when you use insulation to get things to boil you fry the magnet.
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Cathoderay
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[*] posted on 19-2-2023 at 09:00


Quote: Originally posted by Tsjerk  
Yes, and when you use insulation to get things to boil you fry the magnet.

That is not necessarily true.
It depends on the magnet material. Common (and cheap) neodymium magnets can lose their magnetism at as low a temperature of 80 degree C.
https://www.jobmastermagnets.com/how-does-temperature-affect...
Most of the time when stir bars are sold the material type is not specified.
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Mateo_swe
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[*] posted on 20-2-2023 at 06:25


So many hotplate stirrers that are just no good.
I have one of these orange Maple Scientific hotplate stirrers and it works ok.
But they cost a bit more, you get what you pay for.
There are probably better ones for more $$$.

An option if you have a variac is to use a heating mantle sleeve, they are cheap.
These are just the replacement heating element for heating mantles with the surrounding glassfiber insulation.
Works perfect to place on a hotplate stirrer and use the stirring function while heating with the sleeve.
But be careful with live AC voltage.
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