[dese]

I've been trying to make CaO from CaCO3 by burning it with an alcohol burner (which apparently doesn't heat that well). Agricultural "limestone" turned black but apparently wasn't calcium oxide. Antacid pills also didn't give me any calcium oxide, but apparently they're not pure calcium carbonate either. They left me a nice little present on the bottom the tube, though -- looks like a sugar burn and some black spots on the bottom.

Water doesn't help. Neither does vinegar (it's been sitting there for a couple of days). I'm thinking sulphuric acid but I don't have any lying around.

Also, I melted some sugar and have stains on the bottom of my beakers.

Help? =D

[billnotgatez]

Muriatic acid (Hydrochloric acid) is used to clean swimming pools and concrete cement.

You might try a drain cleaner.

Keep in mind that either is corrosive or caustic.
Also do it outside and do not breathe fumes.

[enahs]

You can also buy Acetone at the local hardware store (usually in the painters section). It is good for cleaning stuff.

[dese]

I left some concentrated hydrochloric (~8 molar muriatic) in the beaker for a couple of hours -- it seems to be slowly eating away at the residue. The biggest pain is neutralizing even minute amounts of it, since I don't have any strong bases on hand. Drano crystals aren't anywhere near as concentrated as the acid, and they pack little scraps of aluminum in there for my enjoyment. I'll try acetone after I neutralize the acid.

The sugar burns should still be sugar -- right? would sulphuric acid do the trick?

[constant thinker]

Yes the concentrated sulfuric acid should would work. Take the same precautions though.

Try the acetone first though. Better to use cheaper and safer chemicals than more dangerous and more expensive ones.

[Borek]

Try bleach or other oxidizig agent - like dichromate in sulfuric acid. Note that this stuff can be dangerous. Piranha solution (which I am not suggesting!!!!!) is used for glass cleaning, but it can explode in contact with the organic resiude.

[UnintentionalChaos]

You don't necessarily need a real strong base. Roasting baking soda at 200F or so for a few hours turns it into sodium carbonate (anhydrous washing soda) which is great for neutralizing acid (It doesn't fizz nearly as much as baking soda. Plus, a strong acid will tend to react to completion with even a weaker base. I usually flush sulfuric acid waste (without heavy metals involved) since it is drain cleaner anyway. HCl probably wouln't be an issue either, but I'd keep nitric out of the sewers. I've used a piranha before (with 93% H2SO4 and 15% H2O2. It ate some nasty junk out of my glassware without getting *too* hot or frothing everywhere, probably because the peroxide was weaker than normally used.

I'm also going to mention something that has been mentioned to me, but I have not tried yet. Make magnesium nitrate hydrate and put some in the beaker/test tube. Heat until it dissolves in its own water of crystallization and move it around over the carbon stains. When it seems to stop working, add more nitrate.

[dese]

I'll try the sodium carbonate deal -- curiously, how hot can a wickless alcohol burner heat? I'm thinking of doing that in the test tube, but last time I tried that I had to open this thread.  I have a septic system so I need to be extremely careful as to what I dispose, so pouring out hydrochloric and drain cleaner isn't too much of an option. I left acetone in the tube for a little while, it only dissolved a little of the black (not sugar) residue. I guess I'll try the sulfuric acid, then.

Also, are small (~10mL) amounts of piranha solution reasonably less risky then cleaning in larger amounts (which university pages caution against)? And it can be neutralized with manganese dioxide, then a base?

[UnintentionalChaos]

Just point the test tube away from yourself in case it spatters. Also, make sure there is no organic residue anywhere near the solution (especially with higher conc. peroxide) or it could explode. NaOH solution is ideal for neutralizing since it won't fizz. the resultant mix is still an oxidizer though and should be handled accordingly. I usually just dump the stuff after neutralizing, but oxidizing scrap metal in a waste bucket is a decent way of reducing it to sulfates. It can even eat copper metal at room temperature, which is quite impressive, although it is slow. I'd avoid MnO2. The last thing you need is a frothing tube of conc. sulfuric acid.

An alcohol burner can get pretty hot. Hold a post-1982 penny in the flame for a few minutes. If it sags and appears to be melting (most likely won't make a drop of metal fall unless you shake it a little), that is @800F. My alcohol burner cost me 40 cents and is an olive jar with the lid pierced and a piece of fiberglass tiki-torch wick pulled through. It can boil a 250ml beaker of water in a few minutes, so not too shabby. This is definitively hotter than the tighly woven cotton wick I used to have which had no chance of doing that. You can do the baking soda decomposition in a test tube, since there is no carbon anywhere in the product. The product is a fine, free-flowing bright white powder and will pour out cleanly. It may even appear to "boil" as large amounts of CO2 and water vapor flow upwards through the fine powder. Generally anything food grade is very pure to what the box says it is. The decomposition ,though, is more practical to do in a large batch and baggie it up for later use. A low oven will take several hours to finish though. The hotter, the faster.

[constant thinker]

If you have a septic tank I would avoid dumping any chemical down the drain that has any tendency to react with organics. As we all know septic tanks are filled with a lot of erm organic material so to say.

[woelen]

Stay away from piranha solution, that really is too dangerous, especially if you are not used to handling dangerous chemicals. In the beaker, I first would try to use mechanical cleaning (brushing) and then use acetone. As a last resort, you could try 65% nitric acid and heat this in the beaker (assuring that no acetone remains are left!!). This also is quite dangerous, but not nearly as dangerous as piranha solution. Do this outside, or in a fume hood. When handling the acid, be very careful not to get any on your hand.

[limpet chicken]

I'm surprised nobody mentioned acidified permanganate solution, using 40-50% H2SO4, and NaMnO4/KMnO4 (the sodium salt is a pale lurid shade of green, so doesn't obscure the view of cleaning progress as much as KMnO4.

Don't, of course, go and mix up a stronger solution, as HMnO4 decomposes after a certain concentration, and Mn2O7, is what you will produce if you use concentrated acid (98%), which explodes on contact with organics (and just about anything else too )

[pantone159]

Another option is a base bath, IIRC a recipe is 'about a pound of NaOH/KOH in a gallon of alcohol'.
Note that this is very caustic, more so that just straight NaOH solution, so appropriate precautions are required.

[billnotgatez]

Why would a home chemist try all these odd compounds?

First try acetone
If that does not work
Wash thoroughly
Try a lye based drain unclogger
If that does not work
Wash thoroughly
Try a sulfuric acid drain cleaner

[hmx9123]

Jesus, I would not try the permanganate/sulfuric acid!  That's something for Limpet to mess with.

I agree with Bill's suggestion above.  I guess the other question is why don't you buy new test tubes?  They're cheap.