Australia's Science Forum

I've just bought some Sodium Dichromate to clean stains from glassware, but now our one and only fume hood has died so I'm waiting for the electrician.
I've got the instructions for how much to use and how to mix with Sulphuric Acid etc, but not whether it should be done in fume hood.Does anyone else use this stuff for cleaning and how do you prepare it? With fume hood or without?

In NSW Chromic Acid, which is what you are making, is not used any more. I would use a flume cupboard. If the CSIS say it is a highly dangerous material and other cleaning methods should be used. Sorry not the help you are after.

I just made a litre of Sodium dichromate + Acetic acid and I didn't use the fume cupboard,

didn't really know I had to....my bad. I am still here to tell the story.

That is a bit extreme ,the dichromate and acid.
For 20 years I have used a dilute solution of oxalic acid...works for me.
whilst oxalic acid is poisonous it is less hazardous than dichromate and chromic acid.

What sort of glassware are you needing such strong acid for cleaning.

Be carefull and weigh up is it worth it in the long run using such a strong acid.



KIMMY

Have you tried using napisan? I find that it works really well. Sometime you just have to leave it to soak for a few days and then it is good to go!

Sass

I agree with sassi, I just buy a cheap laundry soaker and leave for a few days then clean as normal, good on rust stains.

Cheers Maria

I changed to using Napisan also. Soak over the weekend and it is clean as. And without dangerous toxic nasties...

Robbie

Go Napisan, see what you can learn here on Chemtalk.

Thanks guys.
It's just regular lab glassware, but some of the stains are really bad, there's rust on some, limescale on others, and unidentified in yet others. I'll try the Napisan next, at the moment they're soaking in citric acid as someone had suggested somewhere, we'll see if that does the job.

Dear Gillian,
pleeeease don't use chromic acid (metal chromate + concentrated acid). It is banned in schools now as an "X" category chemical - highly toxic, carcinogen, forms explosive mixtures with combustible materials, etc.
Once it is made up, it is very time consuming to get rid of.
Hope this helps,
Cheers,
Robyn

Only banned in DET schools NSW. The lady is in NT. So I do not know their laws. Its do hard some times Robyn to give advise, first look at the state/country and go from there.

Laws? NT? Safety Laws? Oh just don't even go there!
Metaphorically I mean, physically, it's a great place to visit.

No really, we have laws now!

Last year they even introduced a speed limit!!

And now they're talking about banning regular people from letting off fireworks in their own back yard!!!

How Draconian is that??????????

When I first came here it took me three weeks of scrubbing just to get the lab glassware clean and free of rust stains. I banned ordinary steel wool for cleaning electrodes and switched to stainless steel wool. I soak the stainless overnight to loosen the soap impregnated in it then rinse clean. It's more expensive but saves so much time cleaning.
I found the best way to remove rust stains is 6M HCl and keep a container just for the odd rust-stained pieces that comes back from teacher demos. It also removes other stains too.
I've just cleaned some almost black dropper bottles used (probably since the college's inception) for silver nitrate and now have new-looking bottles. I used 1/2L conc nitric and rotated the bottles through until all were done. Conc is perhaps a bit extreme and 1:1 will probably do the job but I wanted a quick result. For silver stains on benches and floors I use 'Silvo' silver polish.
The teachers here said I should make up a winchester of chromic acid and save myself some work. I read the MSDS and politely declined!
Cheers
Fran

Yes the fun-suckers are everywhere these days. Mind you regression is always possible in the North. After all, we still get regular calls to go back to Trophy Hunting for crocs. Ah well.

I have some amber dropper bottles that have some kind of salt residue inside (or possibly etched into the glass?). I have tried scrubbing with a test tube brush, soaking in napisan, soaking in HCL (~2M) and while it has marginally improved, They are still quite cloudy to look through. Should I just throw them out? I feel like using more time and chemicals to try and clean them isn't really worth the cost to replace. There are currently only 6 of them although I may find more as I continue my clean-out. What would you do?

I had dozens and dozens of them Rosalie.
I'd attempt to clean them when I had a chance .A year later they were mostly still there .

Sometimes you just gotta do what you know you really need to do .

I binned them and bought new ones

Well actually , I kept a few of the better ones for NaOH droppers s they always end up scungy anyway .

Yep - bin them. Does sound like the NaOH effect, but who knows?

We use 10% oxalic acid for cleaning glassware, could give it a go, not sure if it will work if it's been etched though...