Gargamel
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Barium and sodium hydroxide shelf life
Hi guys,
what do you think, how long can you store barium hydroxide in a normal Merck ect. plastic bottle?
It will react with ambient humidity and CO2 forming Carbonate.
The same goes for natrium hydroxide.
Question is, how long does that take before carbonate reaches more than 1% or so.
I'd like to know what I'm working with - with 99% or more hydroxide, like the label says, or maybe only 92% - or 88% - hard to determine....
But I find it extremely convenient to rely on 99% or more for calculations ect.
[Edited on 30-7-2013 by Gargamel]
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phlogiston
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natrium hydroxide ('sodium hydroxide' in English) is also very hygroscopic, and I think it will acquire water more quickly than
CO<sub>2</sub>. If you need a solution of accurately known concentration, the best way is to dissolve approximately the amount that you
need and then to carefully titrate the resulting solution with an acid of accurately known concentration. Ofcourse, this won't tell you the carbonate
content.
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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bfesser
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When I need NaOH(aq) free of carbonate, I prepare it by dilution of saturated NaOH(aq) with degassed (freshly distilled) water.
<a href="http://pubs.rsc.org/en/Content/ArticleLanding/2000/AN/a910335j" target="_blank"> | Quote: | | Carbonate can be removed from highly concentrated (ca. 50% w/w) NaOH solutions by filtration since Na2CO3 is almost insoluble in
this medium. <img src="../scipics/_ext.png" /> |
</a>My original reference for this comes from a
lab manual I used at university:
| Quote: | <strong>(<em>c</em> Preparation of 0.1 M Carbonate-free Sodium
Hydroxide</strong>
Boil 1 liter of deionized water for approximately 5 minutes in a Florence flask. Do not
fill the flask to the neck or it may boil over violently; place a stirring rod or a thermometer in the flask to prevent "bumping." When boiling is
completed, let the water cool for 10 minutes, then seal the flask with a <strong>rubber</strong> stopper. Let cool (use an ice bath to
facilitate cooling, or let sit overnight); then add about 7 ml of <strong>saturated NaOH (17 M)</strong> stored in the base hood to the
cooled H<sub>2</sub>O. Saturated NaOH is used to make a dilute solution of NaOH—<strong>not solid NaOH
pellets.</strong> This is because solid NaOH always contains some Na<sub>2</sub>CO<sub>3</sub>. We do not want
Na<sub>2</sub>CO<sub>3</sub> in our NaOH titrant solution because the equivalent molecular weight of
Na<sub>2</sub>CO<sub>3</sub> is different from that of NaOH, i.e., if a sample contains equal weights of NaOH and
Na<sub>2</sub>CO<sub>3</sub> then the amount of HCl needed to neutralize NaOH will be different from the amount of HCl used to
neutralize Na<sub>2</sub>CO<sub>3</sub>. Fortunately, nature is kind. Na<sub>2</sub>CO<sub>3</sub>
is essentially insoluble in a saturated solution of NaOH (ca. 17 M), so that the saturated liquid contains very little
Na<sub>2</sub>CO<sub>3</sub>.
After adding the saturated NaOH, <strong>shake the solution
thoroughly</strong> and allow it to cool to room temperature before standardization. The flask should be capped with a <strong>rubber
stopper</strong> when not in use to minimize the absorption of CO<sub>2</sub>. We do not use a glass stopper or store NaOH in a
volumetric flask because any stray base etches glass (dissolves silica!). As a result, a ground glass stopper can become welded to the flask, thus
ruining the flask. |
— <strong>CHEM 2111 Introductory Analytical Chemistry Lab
Manual</strong>, Fall 2007, Department of Chemistry, University of Minnesota.
It then continues on to standardization of the titrant. The writing in the manual may not be great, but I learned more in that class/lab than any
other.
[Edited on 30.7.13 by bfesser]
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MrHomeScientist
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<a href="http://pubs.rsc.org/en/Content/ArticleLanding/2000/AN/a910335j" target="_blank"> | Quote: | | Carbonate can be removed from highly concentrated (ca. 50% w/w) NaOH solutions by filtration since Na2CO3 is almost insoluble in
this medium. <img src="../scipics/_ext.png" /> |
</a>
I actually tried this with my NaOH, and did not see any carbonate precipitate at all. My supply is at least 3 years old, and has been stored in a
ziploc bag inside another ziploc bag. That's not the ideal storage situation by far, and I thought for sure I'd have some carbonate by now.
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papaya
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Quote: Originally posted by bfesser  | When I need NaOH(aq) free of carbonate, I prepare it by dilution of saturated NaOH(aq) with degassed (freshly distilled) water.
<a href="http://pubs.rsc.org/en/Content/ArticleLanding/2000/AN/a910335j" target="_blank"> | Quote: | | Carbonate can be removed from highly concentrated (ca. 50% w/w) NaOH solutions by filtration since Na2CO3 is almost insoluble in
this medium. <img src="../scipics/_ext.png" /> |
</a>
[Edited on 30.7.13 by bfesser] |
This is good to know! Does the rule hold for KOH ?
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bfesser
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<strong>papaya</strong>, that quote links to a paper discussing exactly this, as will this one:
<a href="http://pubs.rsc.org/en/Content/ArticleLanding/2000/AN/a910335j" target="_blank"> | Quote: | | However, for LiOH (ca. 4 M), (CH<sub>3</sub><sub>4</sub>NOH
(ca. 4.5 M) and KOH (ca. 14 M) and less concentrated NaOH (<10 M), treatment with excess solid CaO followed by filtration gave the best results.
<img src="../scipics/_ext.png" /> |
</a>I'm curious to read the rest of the paper, and think it
could be useful to other members, so I will <a href="viewthread.php?tid=25035&page=2#pid294152">request</a> it in
<strong>References</strong>.
Note: Any time I use an inline image (e.g. <img src="../scipics/_ext.png" />
in a quote or near an image, I have linked to an external resource or reference.
[Edited on 30.7.13 by bfesser]
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Gargamel
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Thank you for the input
Do you think the method with the saturated solution will also work for the barium salts?
Also - wait a minute - I just saw that wikipedia gives 0.0024 g/100 mL (20 °C) for the carbonate and 3.89 g/100 mL (20 °C) for the hydroxide.
Since the hydroxide is more than 1600x more soluble, just recrystallise - is it that simple or do I overlook something here?
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Bezaleel
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This should work, but keep the guidelines mentioned above. Manage the air volume in your crystallisation vessel to be as small as possible, use well
boiled water to dissolve the Ba(OH)2 in, etc.
Check the temperature dependence of Ba(OH)2, which is quite spectacular, i.o.w. putting the solution in a refridgerator may increase your yield.
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