[newbiedummy]

I am brand new to chemistry. I recently bought some glassware and books to experiment with. Tonight I decided to test out my hotplate and reflux condenser to make sure I understood how everything worked. So I filled up a 1000ml Erlenmayer flask with about 800ml of tap water and placed it on my hotplate. I then took my 300m coil reflux condenser and connected it to the flask at the 24/40 joints that they both have. I also capped the top of the condenser with a 24/40 glass stopper so that the whole thing was self-contained and then I attached clamps at the joints. I then hooked the hoses to the reflux condenser and started the cold water flowing through the coil from the bottom. Then I turned on my hotplate.

I know water boils at 100c but I wanted to speed things up so I set it at 250c. I sat there for 20 minutes with nothing happening. It's a brand new $650 hotplate and it was hot with the digital display telling me exactly what temp the surface was at so I knew it was working. The flask was pretty full with water but still after 20 minutes not doing anything (I was thinking the solids in the tap water was keeping the boiling temp high). So I cranked up the hotplate to 550c with the intention of lowering it once the boil started. After about 5 minutes the water started to boil from the bottom. Then all of a sudden the water started boiling very good (but the boil was still originating from the bottom and not the top). Then in the blink of an eye my entire 300mm reflux condenser shot to the ceiling and shattered (despite the clamps holding the joints together). Thankfully I had goggles on which I at first thought was dumb to wear since I was only dealing with water. I first thought "man am I glad I tested this with water and not the sulfuric acid and methanol I was eventually going to use" (being covered in sulfuric acid while breathing a poisinous cloud of methanol would not have been good). But then I asked myself "what the hell happened?".

I know it's obvious what happened. The water vapors built up pressure until it sent the condenser sky high. But why did that happen? I mean I set everything up currectly didn't I? I had cold water flowing in from the bottom of the coil at a good rate. Any vapors should have risen, hit the condenser coil, condensed, and fell back down into the liquid to be vaporized again. Why did this not happen? Why instead of condensing did the vapor just build up pressure until it blew? I assume the correct answer would be that so much water vaporized so quickly all at once that it did not have the time to condense and form back into a liquid quick enough and that I need to make sure there is an equilibrium between vaporization (which occurs fast) and condensation (which occurs slow). But the thing is it was only boiling for like a minute. How in the world are you suppose to boil under reflux for many hours when after just a minute or two is enough to build up pressure to blow the condenser sky high? I mean if I had it boil less it wouldn't have been boiling much at all. Or with a reflux condenser are you just suppose to have the liquid boil just a little above a simmer in order to allow time for the vapor to condense and not build up pressure? Any thoughts or comments would be greatly appreciated because if I can create such a disaster with just water then I'm afraid of what my stupidity could bring about with other substances.

[macman104]

Just don't cap it next time.  I wonder if the tap water released enough CO₂ to cause the increase in pressure...

As far as refluxing, if your reaction vessel is too full, you may not see a very efficient reflux.  Also, heating 800mL of water is a little excessive, why not start with something smaller, that will heat quicker?  Also, stirring will help distribute the heat better.

[newbiedummy]

Ok thanks machman. So next time I reflux (after I buy another condenser) I should throw in my magnetic stir rod and flip on the stirring action on my hotplate.

Yeah I figured 800ml in a 1000ml flask was probably too much but I was kind of seeing how long it would take to boil. As far as capping the top of the condenser I'm pretty sure thats what you are suppose to do otherwise the vapors can just evaporate away instead of condense and fall back into solution. But correct me if I'm wrong.... Although I could probably attached a big sep funnel at the top instead which could relieve some pressure while still keeping everything self-contained.

[macman104]

The point is that if the condenser is working correctly, then you shouldn't need to worry about many vapors evaporating off.  The sep funnel idea would be better if you're worried about those things though.  No reflux setup that I've seen is ever completely closed.

[newbiedummy]

No reflux setup that I've seen is ever completely closed.

Ok that right there helps a whole lot. I just assumed that it would be self-contained but if it's not suppose to then that makes everything understandable now. I intend to boil under reflux some things like methanol that gives off a poisonus though so I guess I just have to connect a hose at the top to vent outside then.

[macman104]

Yes, you would want a vent, just in case. 

If you think about your little explosion from a P=nRT/V perspective, you can see that heating a closed system (constant volume) will always cause an increase in pressure (because the T variable is increasing, while V n,R, and V stay constant).  The glass is heated, and the air inside is heated.  If you close the system, the pressure may exceed the strength of the glass.

[nj_bartel]

Just don't cap it next time.  I wonder if the tap water released enough CO₂ to cause the increase in pressure...

I'd think the steam would be a more likely culprit.  800 mLs of boiling water is going to create a lot of it, and whether it makes far progress up into the condensor or not, it's still going to fill the 200 mLs of your flask that were just filled with air previously.

At any rate, gentle heat is the way to go - don't set the temp any higher than you need to (say, 20-30 degrees above boiling point of your mixture).  If you still find vapors escaping the top of your condensor, you could try adding a drying tube to the top of the condensor and fill it with whatever absorbs methanol nicely.  If that still doesn't work, it's kinda up to you whether you think hooking a hose up to the condensor would be easier, or buying some dry ice, solvent, and a pump to run the mixture through your condensor.  Hose would probably be easier.

[Borek]

Water get overheated, when it finally started to boil, it had a lot of excess energy. Add porcelain chips next time.

[billnotgatez]

I wonder if doing this under a hood would be a good idea, especially with methanol and sulfuric acid.

[nj_bartel]

A hood's a pretty big investment for a beginning home chemist.

[newbiedummy]

Thanks guys. Another thing I just thought of is I really made things snowball quickly by capping the condenser by basically building a pressure bomb waiting to explode the minute boiling began and here's why. I capped it off then started heating. Water boils at 100c at 1 ATM but by trapping all the heat, vapor, and expanding air I made the pressure in there much much higher. As a result the water required a much much higher temp to get to boiling. So I increased the temp to very high, the pressure kept building which required even hotter conditions to bring the water to boil which accelerated the pressure build up even more, the snowballing began, and then when the water finally was able to start boiling that kind of ignited all the pressure build up. So I guess that's why it blew after only a minute of boiling because there was already so much pressure build up stored and the water probably was at 200c before it started boiling. Well now I know and I should be thankful that only the condenser went for a ride instead of me having to pick glass shrapnel out of my body all day from the whole thing blowing up.

[Arkcon]

A hood's a pretty big investment for a beginning home chemist.

Then perhaps the entire procedure is not meant for the home user?  Perhaps it's worthwile, to start small, under a professional instrtor's supervision, in a university lab environment?  In particular:

I know water boils at 100c but I wanted to speed things up so I set it at 250c.

No.  You don't do that.  Ever.  It is not justifiable.  At all.  Ever.  A careful, cautious person, who wants quality results, never does that.  Heck.  If you want to cook dinner, any recipe will tell you, put the heat on medium, or medium high, and monitor the process, reducing the heat when the process seems to be running away from you.  Yeah, you can make ramen noodles on high, and burn half of them into the walls of the pot. But that's not how a chemist works.

'Tho I do have to admit, I am pretty proud of newbiedummy: for starting out with water and not dangerous reagents.  Doing a dry run is a pretty impressive insight, as "basement bombers" go.  Please spend more time reading your text, before you try this again, and try to find a laboratory text, or a children's book of chemistry.  Wherever the children's book of chemistry says, "Get an adult." you should take that tio mean, step back, metaphorically, and say "What can go wrong, right here, right now."  and formulate a plan.

Yeah I figured 800ml in a 1000ml flask was probably too much but I was kind of seeing how long it would take to boil.

Likewise, when I started chemistry, not overfilling a flask was the first thing taught to me.  People who insisted they should do whatever they felt like in the lab got thrown out, physically if necessicary.  And probable devoted their mind power to law, or politics, instead.

[newbiedummy]

^^^ Thanks, I appreciate it. And I did look into learning chemistry on a campus but even the community colleges require several requirements just to get into intro classes. It wouldn't be for 2 years before I even got to a lab class. I don't have the time or money for that. And based upon my finance and business degrees where for 4 years %90 of what I learned was anything but business or finance it would not be worth it anyways (unfortunately colleges are just big businesses). What I learned yesterday cost me a $60 condenser, through college would have took me $15k and 2 years.

Oh and also, just because you set a hotplate at 250c does not mean that is the temp the solution will get. If you set a hotplate at just 100c or even 110c then water will never boil on it.

[Borek]

What I learned yesterday cost me a $60 condenser, through college would have took me $15k and 2 years.

Are you suggesting all you will learn in the college in two years is the information how to NOT blow condenser? If so, I agree - it is a waste of money

Oh and also, just because you set a hotplate at 250c does not mean that is the temp the solution will get. If you set a hotplate at just 100c or even 110c then water will never boil on it.

Put a thermometer into water to check what is its temperature.

And don't forget to add porcelain chips. Always.

[sMgz]

^^^ Thanks, I appreciate it. And I did look into learning chemistry on a campus but even the community colleges require several requirements just to get into intro classes. It wouldn't be for 2 years before I even got to a lab class. I don't have the time or money for that. And based upon my finance and business degrees where for 4 years %90 of what I learned was anything but business or finance it would not be worth it anyways (unfortunately colleges are just big businesses). What I learned yesterday cost me a $60 condenser, through college would have took me $15k and 2 years.

Oh and also, just because you set a hotplate at 250c does not mean that is the temp the solution will get. If you set a hotplate at just 100c or even 110c then water will never boil on it.

Talk to an administrator in the chemistry department. In my school, there are two different organic chem lab courses, one for chemistry majors and chemical engineers, that need to fully understand everything that's going on chemically, and one for people that need to learn how to be safe in the lab and how to use equipment safely that can just follow the directions on the page for everything chemistry-related.