Sciencemadness Discussion Board

Yellow stain on glassware

TheChemiKid - 29-12-2013 at 03:54

I bought a second hand chemglass reflux condenser a while ago. When it arrived, it had a yellow stain on the inside of the cooling coil.
Even though this is on the inside of the coil and doesn't effect its usability at all (It works amazingly), I was wondering what this was caused by, whether it could be removed (I know cleaning things is already a thread, but since I don't know what this is, I don't know how to clean it), and whether it is a problem or not.

PS: Would it be possible for the cleaning method to not be caustic or toxic?

I will be posting pictures soon.

papaya - 29-12-2013 at 04:01

Obviously a rust.

TheChemiKid - 29-12-2013 at 04:05

Why would that be?

bahamuth - 29-12-2013 at 04:43

It is simply minerals deposited from the water that has passed through it.

You might be able to remove it with dilute hydrochloric or nitric acid, but me I'd just whip up some aqua regia and let the whole thing soak in it for a day or two. I like my glass spotless, and as such a KOH/ethanol wash would follow the aqua regia soak...

Acetic acid or citric acid might remove the stain too, but I suspect a prolonged soak would be needed, even boiling perhaps..

TheChemiKid - 29-12-2013 at 04:47

Thank you, I will try different methods and say how they perform.

Random - 29-12-2013 at 08:21

Iron stains are very hard to remove from glassware. If it doesn't get removed by HCl you might want to try aqua regia.

Sublimatus - 29-12-2013 at 10:22

You might try a mix of dilute hydrochloric acid and hydrogen peroxide. That mixture removes many otherwise tenacious stains, in my experience, and is a lot safer than aqua regia.

Zephyr - 29-12-2013 at 10:42

I usually clean rust off of my glassware buy soaking the dirty equipment in a hot solution of oxalic acid. This method has the perks of being efficient as well as non toxic.

Pyro - 29-12-2013 at 11:32

I acquired a lot of condensers that all had yellow stains in them, I found HCl to be of limited use. Chromic acid cleaned it right up though, and I prefer chromic acid as it doesn't fume like HCl and HNO3!

Metacelsus - 29-12-2013 at 15:48

For really dirty glassware, I usually use saturated sodium chlorate solution and 31% hydrochloric acid. The chloric acid/chlorine oxides produced will oxidize away all the dirt. (It's like chromic acid, but no heavy metals.) Fumes, however, are a problem, so I do it outside.

Don't try using concentrated sulfuric acid instead of the hydrochloric acid. I did, and I'm lucky the resulting explosion didn't crack my glassware.

[Edited on 29-12-2013 by Cheddite Cheese]

Pyro - 29-12-2013 at 18:52

thats true, but I hate HCl fumes!

have you tried that mix on orgo crap left over from distillation? those terrible tars that stick to everything.

Metacelsus - 29-12-2013 at 19:14

Actually, I first tried it on tar (aldol condensation crap impurities) left over from distilling crude chloroacetone. After a soak overnight, it came right off.

Pyro - 29-12-2013 at 19:30

it takes all night? well, I guess I'm just lazy (must be why my lab is so damn tidy :))

macckone - 29-12-2013 at 19:33

Quote: Originally posted by Pinkhippo11  
I usually clean rust off of my glassware buy soaking the dirty equipment in a hot solution of oxalic acid. This method has the perks of being efficient as well as non toxic.


Oxalic acid is actually toxic to humans.
More so than HCl.
However it is a very good cleaner for rust stains and
is sold for that purpose.

Eddygp - 30-12-2013 at 10:07

If it is iron, oxalic acid is usually your best bet. I remember watching a video in YouTube some months ago about cleaning rust... check it in case it's there.

Brain&Force - 30-12-2013 at 11:03

I've never tried this, but if you can get ahold of EDTA, that may work to chelate the iron away. Acidic citrates also work, they're probably the least toxic solution.

There's also stuff called naval jelly, it's mostly phosphoric acid. It seems to work pretty well, as does ammonium dihydrogen phosphate.

Zephyr - 30-12-2013 at 11:27

Quote: Originally posted by macckone  

Oxalic acid is actually toxic to humans.
More so than HCl.
However it is a very good cleaner for rust stains and
is sold for that purpose.


Yes you are right, isn't the oxalic acid in rhubarb leaves that make them poisonous?
I think this is the video you were thinking about Eddygp?

macckone - 30-12-2013 at 14:44

Quote: Originally posted by Pinkhippo11  

Yes you are right, isn't the oxalic acid in rhubarb leaves that make them poisonous?


Yes and it is a cumulative toxin.
If forms kidney stones which in sufficient quantity cause
the kidneys to shut down.
Spinach also contains oxalic acid but it binds with
calcium also found in spinach to prevent it from being
absorbed. You have to eat pounds of rhubarb
to actually poison yourself. Antifreeze (ethylene glycol)
is converted to oxalic acid which makes it toxic.

http://helios.hampshire.edu/~nlNS/mompdfs/oxalicacid.pdf


bahamuth - 30-12-2013 at 18:20

While on the subject of oxalic acid toxicity.
My uncle almost died as a kid from rhubarb wine (which he stole from my grandfather) that had not been "calcified", in other words added a soluble calcium salt, most likely Ca(OH)2

I have no idea what they did to save him though...

macckone - 30-12-2013 at 23:56

Quote: Originally posted by bahamuth  
While on the subject of oxalic acid toxicity.
My uncle almost died as a kid from rhubarb wine (which he stole from my grandfather) that had not been "calcified", in other words added a soluble calcium salt, most likely Ca(OH)2

I have no idea what they did to save him though...


Probably pumped his stomach, balanced his blood ph and calcium levels with fluids

Most poisoning is not fatal but does lead to kidney stones.

Fantasma4500 - 31-12-2013 at 04:45

i found it that Fe3O4 reacted very well with concentrated citric acid + H2O2
as i heated it it gave off a nearly explosive decomposition
the Fe3O4 was 'beach magnetite' and some of might be iron aswell

but ofcourse, the more dangerous the chemical is, the more reactive it is, so the more dangerous stuff you use for it, the bigger the chances are it will get rid of it (:

Arthur Dent - 1-1-2014 at 13:41

THe idea of oxalic acid is interesting, although this chemical is pretty hard to find at reasonable prices in my neighborhood.

As for the HCl + bleach solution, it is indeed very efficient to remove most ferrous stains, but to my dismay, it also destroyed the company logo off of my expensive Ace Glass Soxhlet... The red logo turned dark brown, and while washing with soapy water and a brush, just disappeared! :mad: I thought that such a prestigious labware maker would make their logo a wee bit more resistant to mineral acids.

LOL

Robert

macckone - 1-1-2014 at 19:05

Bar Keepers friend contains Oxalic acid as well as other scrubbing agents. There are also sulfamic acid cleaners (ZEP CLR for one). And of course the good old cheap standby of vinegar and hydrogen peroxide. One of the sulfamic acid cleaners may be better as they
are specifically formulated to remove rust stains from ceramics.