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Author: Subject: Sodium chlorate-proprieties
MeshPL
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[*] posted on 22-5-2015 at 09:36
Sodium chlorate-proprieties


Hello everyone!
I wanted to make some KClO3, but getting decent amount of KCl here where I live is close to impossible. Ordering from the internet or "Lo-salt" are somewhat expensive, KCl as water softener is unavailable, KCl as fertilizer is nearly unavailable, while chemical supply shops are non-existent :(.

So I wanted to make NaClO3. Wikipedia says it is higroscopic and I have a few questions:
-how higroscopic is it?
-can I store it in a jar or plastic bag without serious degradation?
-can I dehydrate it by heating? What temperature will I need?
-are there any other proprieties I must be aware of?

I'm not going to store pyrotechnical mixes, just "pure" NaClO3

Also, I've read I have to remove CrO42- before crystalization. Is it true?
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[*] posted on 22-5-2015 at 11:35


If you recrystallize your sodium chlorate, it will remove almost all of the chromate.

It's about as hygroscopic as sodium nitrate, in my experience. Storing it in a sealed container (a plastic bag inside a jar, perhaps) will prevent it from absorbing water.

Yes, you can dehydrate it by heating, but don't overheat it, and make sure that it doesn't have organic (fuel) contaminants before you do so.




As below, so above.
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[*] posted on 22-5-2015 at 12:18


Ok. Thanks! Just one more question:

Do I need to recrystalize NaClO3 to remove Na2CrO4 or I can leave it out, if do not need high purity?
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[*] posted on 22-5-2015 at 13:01


Recrystallisation purifies it of whatever is in solution.

Do not be greedy.

Dump a lot of the supernatant liquid to get the best purity, even though you are also dumping a lot of impure product.




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[*] posted on 22-5-2015 at 13:25


How crucial is purity for safety? Is chromate contamination really bad?

Ok, there are some nasty kinds of contamination. But I don't think I will have them in my cell.
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[*] posted on 22-5-2015 at 14:41


You can find the approximate relative humidity that many materials become hygroscopic (absorb water from the air) by using the solubility of them in water.

The following are quotes from the short question quick answer thread:
http://www.sciencemadness.org/talk/viewthread.php?tid=26572&...

>You can make a first approximation based on the molar fractions
>of the ionic solutions. For example, take NaNO3 at 20 degrees.
>100 gm of water is 100/18 = 5.56 moles. 87.6 gm of NaNO3 is
>87.6/85 = 1.03 moles, which in solution is twice that number, or
>2.06 moles of ions. The molar percentage of water is then
>5.56 / (5.56 + 2.06) = 72.9%, which, to a first approximation is
>the vapor pressure as a fraction of the 100% relative humidity pressure,
>and hence the humidity at which a saturated solution will pull moisture
>from the atmosphere

"A material is said to be hygroscopic when it absorbs moisture from the air at ordinary temperatures and humidity. This occurs when the pressure of water vapor in the air exceeds that of the saturated solution of the material."

For NaClO3 at 25C:

105.7g / 106g/mol * 2 = 1.986 moles of ions
100g H2O / 18g/mol = 5.56moles
5.56 / (5.56 + 1.986) * 100% = 73.7%


For NaNO3 at 25C:

91.2g / 84.9947g/mol * 2 = 2.146 moles of ions
100g H2O / 18g/mol = 5.56 moles
5.56 / (5.56 + 2.146) * 100% = 72.2%

So, yeah, sodium chlorate and sodium nitrate should be approximately equally hygroscopic.


[Edited on 22-5-2015 by Hennig Brand]




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[*] posted on 22-5-2015 at 14:53



Needing chromate in chlorate cells is an obsession imo.

In Ullman. Chlorine Oxygen acids and salts it says

Cathodic Reduction of Hypochlorite. The
main loss occurs by cathodic reduction of hypochlorite,
as described in Section 4.2.1:
ClO− + H2O+2e −→ Cl− + 2 OH−
The reaction competes with hydrogen generation.
Without special precautions, its rate is
controlled by mass transfer and, therefore, linearly
proportional to the hypochlorite concentration
in the bulk electrolyte. The reaction can
widely be suppressed by adding a small amount
of dichromate (1 – 5 g/L) to the electrolyte solution.
By cathodic deposition a porous surface
film of chromium hydroxide forms [169]. Inside
the pores of this film, the effective current density
increases, and the resulting potential gradient
across the film impedes the diffusion of any
kind of anions to the cathode, whereas the access
of cations to the cathode and their reduction are
facilitated. The protective film ceases to grow
after a certain thickness is reached; the increase
in cell voltage caused by the ohmic resistance of
the film is more than compensated by the gain
in current efficiency [165], [170]. Increasing the
electrolyte temperature favors mass transfer of
hypochlorite to the cathode and, therefore, requires
more dichromate. When the current is interrupted,
the surface layer dissolves. It takes
some time to reestablish a new film after the current
is switched on, but cathodic reduction immediately
takes place. Therefore, cells should be
operated continuously, and a minimum cathodic
current density is recommended to prevent dissolution
of the film [171]; from industrial experience,
a current density of 20 A/m2 is considered
satisfactory.

Cathodic Reduction of Chlorate. Chlorate
is also reduced at the cathode, but this reaction
is less significant than the reduction of hypochlorite
described in the preceding paragraph:






Just use a small cathode and cover the side of the cathode that in not in direct line of site to the anode with plastic. The side of the cathode not in direct line of site to anode will have low current density and may be reducing Hypochlorite back to salt.
This method will increase voltage accross cell a wee bit but it will be not noticed by all home producers. Industry could not tolerate this.

LEAVE THE CHROMATE OUT OF THE CELL (so there you have it ) :cool::P
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[*] posted on 22-5-2015 at 15:28


Wow Hennig Brand, thanks for that gem, I hadn't heard or thought of that before!



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[*] posted on 22-5-2015 at 18:46


You are welcome. I saw the idea briefly quite some time ago, but it didn't completely sink in until recently.



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[*] posted on 22-5-2015 at 18:59


Hennig:

If you look at the original pretty pictures thread, in one of the last pages you can see my solution to cathodic reduction. Nobody bothered to ask, so I didn't explain. If I told you the current efficiency I was getting you'd call me a liar or bad at math.

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[*] posted on 22-5-2015 at 19:05


Sounds good, I would like to hear about it. I will track down your posts and have a look. The OP and others following this thread might benefit too.



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[*] posted on 22-5-2015 at 21:14



Quote:

Jock88 said:
LEAVE THE CHROMATE OUT OF THE CELL (so there you have it ) :cool::P

(...)

Just use a small cathode and cover the side of the cathode that in not in direct line of site to the anode with plastic. The side of the cathode not in direct line of site to anode will have low current density and may be reducing Hypochlorite back to salt.
This method will increase voltage accross cell a wee bit but it will be not noticed by all home producers. Industry could not tolerate this.

Ask woelen and he will say exact opposite. There just seems to be chromate enthusiasts and opponents.

I'll do some experiments on chromate addition.

Also I can' t cover any part of a cathode-it's completely surrounded by anodes! (With keeping 2cm distance) :P.


[Edited on 23-5-2015 by MeshPL]
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[*] posted on 23-5-2015 at 08:58


http://www.sciencemadness.org/talk/files.php?pid=295780&...

Very bottom of page 39.
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[*] posted on 23-5-2015 at 09:12


Yes, I saw that. So you have the cathode surrounded by anodes, evenly spaced. Do you mind explaining a bit?



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[*] posted on 23-5-2015 at 11:35



Nice 'gattlling gun' of an electrode system there Varmint.

IMO (for whats it worth) is that you have eliminated cathode reduction.

Most home cells have just the one flat anode + 1 or 2 flat cathodes which (you would imagine) have low CD on the (back) sides away from the anode = cathode reduction of hypo on the 'back sides'


An extreme example of very bad cathode here.

http://oxidizing.typhoonguitars.com/chlorate/cat_size.html


The *AC and **PC camps are in constant battle with each other. Its an entrenched, bitter, long lasting savage battle (let me tell ya). :D

As a home producer I am inclined to leave stuff out that may possibly interfear with pyro stuff etc down the line. Thats not to say you cannot use and remove chromates. You can. I don't even know if chromates are a problem with pyro stuff if not properly removed.

* Anti chromate
**pro chromate
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[*] posted on 23-5-2015 at 18:43


As Jock says, reduction at the cathode is reduced or eliminated, both by full coverage by the anodes, as well as intrinsically higher cathode current density.


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[*] posted on 24-5-2015 at 02:30


Maybe to solve the chromate problem...addition of a few drops of solution of AgClO4 or Pb(ClO4)2 until precipitation of colorful precipitate stops might be a good way.

It will aswel take care of the chloride anion that will precipitate as AgCl and PbCl2.

The resulting silver chromate will precipitate red (Ag2CrO4) and the lead chromate will precipitate yellow (PbCrO4).

The perchlorate traces then introduced will give no troubles with the chlorate.

If traces of Ag(+) or Pb(2+) are a problem...add a little Na2CO3 to get Ag2CO3 or PbCO3 precipitate.

If you used Silver ...recollect precipitate for recycling of silver.

Another solution might be to use aceton as extraction media for the chlorate and perchlorate.
Solubility of perchlorate > chlorate >> chloride in aceton. But I don't know solubility of chromates in aceton.

Edit:
This might help monography of chromium
http://monographs.iarc.fr/ENG/Monographs/vol49/mono49-6.pdf

[Edited on 24-5-2015 by PHILOU Zrealone]




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[*] posted on 24-5-2015 at 05:03



Barium Chloride is added in industry to remove chromates. Barium Chromate is very insoluble.

The easy way is to add no chromate!
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[*] posted on 24-5-2015 at 10:29


Here is a document describing a commercial sodium chlorate production process. They mention electrode size and spacing as being important for efficient operation, but they also put a lot of emphasis on circulation.

Attachment: Sodium Chlorate Technology InfoSheet.pdf (834kB)
This file has been downloaded 265 times





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[*] posted on 24-5-2015 at 14:16



We should always remember that documents like this are showing you how to squeeze the last few % current effeciency points out of the process.
If you bung any old cell together with no pH controll just about any old cell will achieve about 50%.
With any old cell with pH controll you will get 80 or 90 %.
From then on things get harder and harder to gain % points. The state of the art the guys in the paper are at is somewhere the home maker will probably never be.
Circulation or 'short time between electrodes' is to stop as much as possible of what is called 'anodic chlorate formation'. (the 9 electron route). You will get some if the intermediates are coming in contact with the anode. You sweep the intermediates away from the electrodes so that they can get on with going the '6 electron route'
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[*] posted on 25-5-2015 at 03:12


Is it even possible for hobbyists to produce NaClO3 with a useful purity?

Since the difference in solubility of NaClO3 and NaCl are not to great. Most people separate the chlorate by metathesis with KCl, however what if you want the Na salt? Or like the threadstarter, have no KCl?
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[*] posted on 25-5-2015 at 04:48


Quote: Originally posted by dangerous amateur  
Is it even possible for hobbyists to produce NaClO3 with a useful purity?

Since the difference in solubility of NaClO3 and NaCl are not to great. Most people separate the chlorate by metathesis with KCl, however what if you want the Na salt? Or like the threadstarter, have no KCl?

If you read a little more carrefully what is written above in the tread that is not so long, you would see the answer to your question.




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[*] posted on 25-5-2015 at 06:59



If you keep adding salt solution to the set up solid sodium chlorate will start to appear on the bottom of the cell (just the same as with KClO3 but it takes longer to 'fill up the pipeline'). This can be washed (and recrystallized if you want.)

Don't use sodium chlorate in pyro stuff or you will get damaged.
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[*] posted on 26-5-2015 at 03:50


The Acetone process sounds interesting, but Acetone is no longer OTC in the EU.

Quote: Originally posted by jock88  

If you keep adding salt solution to the set up solid sodium chlorate will start to appear on the bottom of the cell (just the same as with KClO3 but it takes longer to 'fill up the pipeline'). This can be washed (and recrystallized if you want.)

Don't use sodium chlorate in pyro stuff or you will get damaged.


Why would sodium chlorate drop out first? Would this not include a lot of chloride?
How do you recrystalise 2 salts with identical solubility? Heating would enlarge the difference, but it's still not very great.
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[*] posted on 26-5-2015 at 05:08


Quote: Originally posted by dangerous amateur  
The Acetone process sounds interesting, but Acetone is no longer OTC in the EU.

In Belgium, center of the EU, you will find aceton in big departement stores and medium stores like Carrefour and Supermarket, in Brico shops, in garden shops like AVEVE and in "drogisteries" (shops that sells chemicals and paints).

I think you are misinformed.

[Edited on 26-5-2015 by PHILOU Zrealone]




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