I was “dumb” enough to make barium sulfate and centrifuge it to the bottom of a test tube to show kids a precipitate and the centrifuge working. From what I can find on the net, dissolving this is next to impossible and patents are made just to do this and get the scale out of fluid systems. Is there anything sort of commonly available that will break this down?
I would say nothing economical. I’ve had some small success with sequestering agents, ethylenediamine tetraacetic acid (EDTA) or diaminetriamine pentaacetic acid (DTPA), but it takes a molecule of either to chelate one barium sulfate molecule, so it takes a lot of either.
It is sparingly soluble in dilute sulfuric acid. I don’t know if your students can do this on their own, but if you add some BaSO4 to some dilute H2SO4 on a slide and heat the slide on a hot plate to evaporate some of the water as the H2SO4 concentrates you’ll get distinctive crystals easily visible through a microscope that can be used to identify it.
I just did a Google looking for images but the results were contaminated by a lot of chemtrail nonsense. You might have better luck, or be more determined.
Back when I was an electroplater, Barium Chloride was the standard reagent to find sulfate concentration in Chrome plating baths. We did exactly what you did as a standard procedure. We reacted an excess of the barium chloride with a known quantity of the chrome bathand centrifuged it. I never had any issue with removing it from the centerfuge though. The force of the water from the faucet was always enough. I would suggest high pressure water. Barium sulfate is not toxic in any way, so I would not worry about it going down the drain.
Second the sulfuric acid. It has a really high dielectric constant and will take care of almost any ionic compound, like your barium salt, toot sweet.
Well, actually not. As I said earlier, BaSO4 is sparingly soluble in dilute H2SO4, as in when you concentrate it and the crystals drop out, you need a microscope to see them, that’s how little of it dissolves. But it’s fun, and easy to do, and if the kids are old enough to trust with the stuff I’d let them, because identifying a compound by a distinctive crystalline structure is the kind of classical method that’s gone the way of the philosopher’s stone.
I’d just buy a new test tube. I know those high G-force rated ones for centrifuges are pretty pricey, but if mechanical cleaning won’t remove the precipitate, I think you’re stuck. Remember, if you’re not part of the solution, you’re part of the precipitate.