Australia's Science Forum

Help,

How do I clean porcelain crucibles that have had magnesium heated/burnt in them
Any ideas greatfully accepted.

You could try using conc HCl. I put them in the sink & use a dropper containing 5M Hydrochloric acid. Watch out, it will spark so make sure you wear safety glasses. You may need to use 10M & leave it for a couple of days. Try using a scourer after you wash the acid out. It may not remove everything but it does help. This is something I invented myself, but maybe others have a safer alternative.

I don't have a safer alternative to HCl, but strong nitric acid is quite good. Again you need to take care and it is a good idea to do this in the fume cupboard.

you guys are a lot braver then i am. i just wash them out and scrub them the best that i can and then keep them separate to be used for magnesium only. not the best solution either but one that works for us. Barb

Another good cleaning aid is Hot Con. Sulfuric Acid.

Place enough Acid into the crucible to submerse the stain then heat this using the technique for heating crucible on top of a Bunsen until it boils. Let this stand until the stain is completely gone.

Otherwise allow for a few days and rinse the crucibles thoroughly and use a scourer to easily remove the solid material.

Just be cautious, due to the hot H[sub]2[/sub]SO[sub]4[/sub].

Hey Fella's
Look at the cost of a crucible + the dangers involved, they are a disposable item, just scrub out and for badly stained ones break up for "porous pot"
Cheers

Before spending time cleaning; - thoroughly check the condition of the crucible in particular the underside for cracks or suspect damage. A firm tap on the "crack" will quickly identify the integrity of the crucible and save fracturing during future use.
Cleaning is any of the above but with consideration to the use of a fume cupboard, following safety procedures and the "comfort zone" of the lab assistant.
IF IN DOUBT< THROW OUT

If you wish to escape having to clean the Crucibles entirely, particularly with strong acids, then keep these aside for use only for that particular experiment. That way you know that a quick clean to remove any loose material will be sufficient.

Hello everyone.
I am a new Labbie. (2 weeks). I am here on my own while the permanent Labbie has taken holidays.
My question is - I have numerous crucible with what looks like burnt magnesium ribbon stains.
Does anyone have any idea how to clean them?
I am looking forward to evolving into a real labbie where I look at road kill in a new light.

Thank you to everyone's idea's.
I think keep them aside for next year sounds good.
I do have chemistry experience but not confident about using high molar acids.
I am looking forward to everyone's input next year hopefully when I get some permanent days or a full time job!
Cheers

Hi All, holidays are nearly upon us, yeah But before you go can anyone help with how to clean silver nitrate, sulphur, sodium hydroxide out of crucibles or do i just throw them away.

Thanks for any assistance
Cindy

why woul you have silver nitrate and sodium hydroxide in crucibles? we never did anything like that.

Because I have "special" teachers. No it was to test electricity in the the solid, molten and/or aqueous states. I don't think he realises how much silver nitrate costs, he half filled 2 crucibles and then melted it what a waste.

Mmm...can't say I've ever had to clean those things out of crucibles either, but just clean out any residues by washing, soaking or scraping. Don't worry about stains. Our seem to crack easily and are therefore thrown out regularly. I used to soak test tubes with melted sulfur stuck to them, in 2m sodium hydroxide for a couple of days and it would come off easily. You could try with the crucibles, just not sure whether porcelain and glass will clean the same.
Ask the special teacher if it is in the syllabus. We only test the solids here, not molten or aqueous.
I have made sulfur blocks for electrical testing: just heat sulfur till molten and poor into ice block tray. They have kept for years, but are now getting broken so will soon have to make some more.

for melting experiment you can use metal lid (Milo tin)

Hi Everyone
I haven't had time to get on here for most of the term. Hope all is well with everyone. This is time consuming I guess but what I have done a few times with crubiles that have been stained is put some water, sand and a magnetic stirrer in the crucible and leave the on the hot plate/stirrer spinning away for awhile and it often works a treat, sometimes if the stain is particularly bad it doesn't though.