barium hydroxide [Ba(OH)2]

S.C. Wack has discussed preparation of barium compounds under the ferrate thread. But I think that barium hydroxide is important enough to merit its own thread.

I needed to prepare a few grams of barium hydroxide. The starting compound I have is BaCO3, readily availabe from pottery suppliers.

I tried 2 methods: (1) ignition w/carbon at 1100C to form BaO, and (2) formation of Ba(NO3)2 w/HNO3 then ignition at 500C to BaO. Addition of water to BaO gives Ba(OH)2 or a hydrate thereof. Here is a summary of my results:

1. Ignition of BaCO3 to BaO with finely ground carbon seemed to be successful. Heated to 1025C (highest my muffle furnace will do) for 1 hour. Weight loss was 24.4% vs theoretical 26.8%.
2. Conversion of BaO to Ba(OH)2 not successful due to considerable absorbtion of CO2 from the atmosphere.
3. Conversion of BaCO3 to Ba(NO3)2 using HNO3 was successful using the theoretical amount of HNO3. Yield was 99.6%.
4. Ignition of Ba(NO3)2 to BaO was not successful. The crucible contents frothed over the edge. A glassine material formed in the bottom of the crucibles. Since my furnace temperature indicator doesn't seem to be accurate in the 500C area I heated the furnace until it just stared to show redness (meter indication: 700C).

So, in playing around with the compounds I found that Ba(OH)2 agressively goes after the CO2 in the air. Everything I tested fritzed CO2 when treated w/10%HCl.

My next attempt will be to convert the BaCO3 to BaCl2 and then convert this to Ba(OH)2 using NaOH per the method in Henderson & Fernelius (our library). This includes some steps to prevent absorption of atmospheric CO2.

The attached photo shows the BaO formed after igniting the BaCO3 at 1025C for an hour.

[Edited on 12-3-2006 by Magpie]

[Edited on 12-3-2006 by Magpie]

[Edited on 12-3-2006 by Magpie]

[Edited on 30-1-2007 by chemoleo]

Yes, it chewed into my porcelain crucibles fairly well. I had a feeling it was fluxing with the wall but thanks for the confirmation. You can see this in the photo.

The Ba(NO3)2 glassine product won't come out of the crucibles. One became brittle and broke when I was cleaning it - this is getting expensive!

This will be a big advantage of the next method - no ignition.

Tell me about it. When I filter my Ba(OH)2 solutions they develop a carbonate layer on top in a matter of *seconds*. Thankfully I'm reacting them with stronger acids than H2CO3, so it shouldn' t matter a lot...

Making Ba(OH)2*8H20 from BaCl2 according to the method in Henderson & Fernelius worked well and I ended up with some nice looking, but wet, crystals. Not able to leave well enough alone I tried to dry these by wrapping them in a paper towel for 24 hours (per another book in our library, Walton IIRC). This didn't work out too well as about half of the crystals effloresced. They also fizzed with 10%HCl whereas the non-effloresced crystals did not. (I thought about separating the crystals by hand then quickly decided that was a bad idea.)

The Henderson & Fernelius procedure for final drying of Ba(OH)2*8H20 to Ba(OH)2 was to place it in a dessicator with - you guessed it - effloresced Ba(OH)2!

Overall, I'd have to say that working with barium salts kicked my ass. My BaCO3 and Ba(NO3)2 ignitions weren't too practical. And when I did get Ba(OH)2 I had to use air purification and sealing to prevent absorbtion of CO2. Although I now think that just working quickly would have worked just as well. But there is more to it than that. The Ba(OH)2 adheres something fierce to all glassware. Then when it absorbs the CO2 you have white stubborn stains. This was removeable with H2SO4 cleaning solution, however.

[Edited on 18-3-2006 by Magpie]

Huge swing in BaOH2 in water

I made some barium hydroxide from barium carbonate using an idea posted by clearly_not_atara (who probably did not intend using impure pottery grade starting materials). He suggested making barium hydroxide by dissolving barium carbonate in dilute acetic acid and then adding sodium hydroxide.

I simply extracted an excess of barium carbonate with 1L of 5% household vinegar in a well-ventilated area, filtered, and precipitated barium hydroxide with sodium hydroxide. Then I heated the mixture to boiling, causing the barium hydroxide to dissolve and did a hot filtration through a coffee filter on top of a cotton ball, placing the flask in a boiling water bath and guiding the steam around the funnel with aluminum foil. At times I used a heat gun to make the mixture in the funnel boil.

Once the filtration was complete, I chilled the filtrate in the refrigerator and then vacuum filtered. The mixture wasn't easy to filter, and to make sure things stayed cold, I dropped a couple of ice cubes in the filter funnel. I also covered it with plastic wrap to keep out carbon dioxide to a large extent. I washed the filter cake a few times with ice cold water.

Here is a picture of the crude product. It is contaminated with a little bit of an extremely fine, brown, silty material that passes through the filter paper (perhaps sulfur?).



The yield I'm sure is not very good, and it will be even worse once I recrystallize, but I'm looking forward to having some barium hydroxide on hand for tests and experiments.

Quote: Originally posted by Magpie

Yes, it chewed into my porcelain crucibles fairly well. I had a feeling it was fluxing with the wall but thanks for the confirmation. You can see this in the photo. The Ba(NO3)2 glassine product won't come out of the crucibles. One became brittle and broke when I was cleaning it - this is getting expensive! This will be a big advantage of the next method - no ignition.

Quote: Originally posted by 12AX7

It's the strongest alkaline earth, no? Beware of glass and porcelain, it'll probably tend to dissolve things, aqueous or glassy state. (Barium is a strong flux, though not much used for toxicity reasons.) Tim