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blogfast25
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Quote: Originally posted by Upsilon  |
4) Dissolving in molten sodium bisulfate. This looks like the most appealing to me, since sodium bisulfate melts at quite a low temperature, but I'm
not sure of the extent to which it will actually dissolve.
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Fusion of TiO2 with excess NaHSO4 works but can take a while.
Fusion of TiO2 with excess KOH gives potassium titanate. Hydrolysis of the titanate with water gives insoluble 'Ti(OH)4' but when freshly precipitated
this 'titanic acid' dissolves easily in 37 % HCl or 50 % H2SO4.
[Edited on 18-9-2015 by blogfast25]
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Upsilon
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by Upsilon |
4) Dissolving in molten sodium bisulfate. This looks like the most appealing to me, since sodium bisulfate melts at quite a low temperature, but I'm
not sure of the extent to which it will actually dissolve.
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Fusion of TiO2 with excess NaHSO4 works but can take a while.
Fusion of TiO2 with excess KOH gives potassium titanate. Hydrolysis of the titanate with water gives insoluble 'Ti(OH)4' but when freshly precipitated
this 'titanic acid' dissolves easily in 37 % HCl or 50 % H2SO4.
[Edited on 18-9-2015 by blogfast25] |
That would require significant temperatures, no? And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for
such a thing.
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blogfast25
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| Quote: Originally posted by Upsilon |
That would require significant temperatures, no? And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for
such a thing. |
Melting points only. Of course you need steel (better even nickel) to fuse with KOH.
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ave369
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| Quote: Originally posted by Upsilon | | And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing. |
They do, but, apparently, their effect on porcelain is negligible (I've melted KOH in porcelain crucibles without damage to them). My only case of
ruining a porcelain crucible was when I was scraping fused pyrosulfate from it too vigorously.
[Edited on 18-9-2015 by ave369]
Smells like ammonia....
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Upsilon
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| Quote: Originally posted by ave369 | | Quote: Originally posted by Upsilon | | And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing. |
They do, but, apparently, their effect on porcelain is negligible (I've melted KOH in porcelain crucibles without damage to them). My only case of
ruining a porcelain crucible was when I was scraping fused pyrosulfate from it too vigorously.
[Edited on 18-9-2015 by ave369] |
Sounds good then. I'd like to note that I mixed some titanium dioxide and highly concentrated KOH solution for the fun of it, and it has been mildly
fizzing for hours now. Not really sure what it means but I'll let it keep going.
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blogfast25
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| Quote: Originally posted by Upsilon |
Sounds good then. I'd like to note that I mixed some titanium dioxide and highly concentrated KOH solution for the fun of it, and it has been mildly
fizzing for hours now. Not really sure what it means but I'll let it keep going. |
I tried that years ago with 50 % NaOH and it didn't put a dent in the TiO2. Let me know what you find.
[Edited on 19-9-2015 by blogfast25]
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Upsilon
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Forgot to mention that I squirted some weak hydrogen peroxide in there as well. It only seems to fizz when I stir it so it's probably just the
peroxide decomposing.
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Upsilon
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Ok, so my little beaker of titanium dioxide and potassium hydroxide has been sitting for several days now. I still saw solid titanium dioxide at the
bottom so I figured I should just pull the plug and free up a beaker. Upon adding concentrated HCl to the mixture to neutralize the KOH, however, it
bubbled extremely violently. This is not typical of a regular strong base-strong acid reaction. What's happening here?
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ave369
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Maybe the heating up caused by neutralization kicked hydrogen chloride from the solution. Highly concentrated HCl releases the gas even on slight
heating.
Smells like ammonia....
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Upsilon
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| Quote: Originally posted by ave369 | | Maybe the heating up caused by neutralization kicked hydrogen chloride from the solution. Highly concentrated HCl releases the gas even on slight
heating. |
Possibly. I ended up dumping it out. I think I'm going to try fusion with sodium bisulfate first; I think it's a good idea to try something easier
before I dive into using molten KOH. What's the reaction that goes on with molten bisulfate?
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woelen
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| Quote: Originally posted by Upsilon | | [...]Upon adding concentrated HCl to the mixture to neutralize the KOH, however, it bubbled extremely violently. This is not typical of a regular
strong base-strong acid reaction. What's happening here? |
This certainly is not due to HCl bubbling out of
solution. Even if it heats up you won't get enough free HCl (remember, most of it is neutralized by the KOH) to bubble out of solution. Even 30% HCl
requires near boiling temperatures for loss of HCl and even then, it contains a lot of water vapor as well.
What actually happened is that the KOH-solution absorbed CO2 from the air. If it is allowed to stand in a beaker for several days, even if this beaker
is loosely covered, then it can pick up considerable amounts of CO2. Hydroxide in aqueous solution is very eager to pick up CO2:
2OH(-) + CO2 --> CO3(2-) + H2O
So, your solution of KOH turns into a solution of K2CO3.
If you add acid to such a solution, then the carbonate is converted to carbonic acid, which in turn decomposes to water and CO2:
CO3(2-) + 2H(+) --> H2CO3 --> H2O + CO2
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Upsilon
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| Quote: Originally posted by woelen | | Quote: Originally posted by Upsilon | | [...]Upon adding concentrated HCl to the mixture to neutralize the KOH, however, it bubbled extremely violently. This is not typical of a regular
strong base-strong acid reaction. What's happening here? |
This certainly is not due to HCl bubbling out of
solution. Even if it heats up you won't get enough free HCl (remember, most of it is neutralized by the KOH) to bubble out of solution. Even 30% HCl
requires near boiling temperatures for loss of HCl and even then, it contains a lot of water vapor as well.
What actually happened is that the KOH-solution absorbed CO2 from the air. If it is allowed to stand in a beaker for several days, even if this beaker
is loosely covered, then it can pick up considerable amounts of CO2. Hydroxide in aqueous solution is very eager to pick up CO2:
2OH(-) + CO2 --> CO3(2-) + H2O
So, your solution of KOH turns into a solution of K2CO3.
If you add acid to such a solution, then the carbonate is converted to carbonic acid, which in turn decomposes to water and CO2:
CO3(2-) + 2H(+) --> H2CO3 --> H2O + CO2
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That's it, then. It was definitely sitting uncovered for several days. Thanks for the explanation.
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MeshPL
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In my school I saw a video of glass etching. What they did, is they poured H2SO4 on NaF and put a glass plate on that container so that HF fumes ( ) can etch it. So they let HF fumes into the air. And it wasn't inside glovebox.
Maybe not even in fumehood. And it was video by our chemistry book publisher. Without a single warning of how gaseous HF dangerous is.
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DFliyerz
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I love living right near Seattle, I was able to go there in person and buy a whole bunch of chemicals that would have been a pain to get elsewhere.
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chloric1
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| Quote: Originally posted by DFliyerz | | I love living right near Seattle, I was able to go there in person and buy a whole bunch of chemicals that would have been a pain to get elsewhere.
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Considering the low cost of their chemicals, it still advantageous for me even though I am just under 2000 miles from Seattle pottery supply. The
low prices more than compensate for transcontinental shipping. Customer service is above par as well.
Fellow molecular manipulator
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DFliyerz
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| Quote: Originally posted by chloric1 |
Considering the low cost of their chemicals, it still advantageous for me even though I am just under 2000 miles from Seattle pottery supply. The
low prices more than compensate for transcontinental shipping. Customer service is above par as well. |
When I went there they said that they get a lot of chemistry hobbyists buying stuff from them, and that some of their sales staff actually used to
work in pyrotechnics.
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