Sciencemadness Discussion Board

Sodium Bromate

kadriver - 7-11-2012 at 05:09

New to the forum - can someone point me in the right direction?

I am looking for a way to make some sodium bromate.

Thank you,

kadriver

woelen - 7-11-2012 at 06:15

What effort did you put yourself in this question? This is not a spoonfeeding forum.

There are quite some threads on making bromates. I actually have a complete web page about that on my website. Please use the search page. The most important thread on bromates is here:

http://www.sciencemadness.org/talk/viewthread.php?tid=224

Next time try to do some research yourself.

kadriver - 7-11-2012 at 07:15

Will do, thanks for pointing me in the right direction.

Kadriver

Sodium Bromate

kadriver - 12-11-2012 at 18:21

I found this video that describes a method for producing sodium bromate.

http://www.youtube.com/watch?v=PojvwUcMK4E

I wonder if the person who made the video is a member here?

Does anyone have any comments concerning this method as described by the video?

Does it look like the process is accurate and would it work as described?

Thanks!

kadriver

woelen - 13-11-2012 at 12:51

This video looks VERY much like what I have described on my website:

http://woelen.homescience.net/science/chem/exps/KBrO3_synth/...


Synthesis of potassium periodate also is described on my website:

http://woelen.homescience.net/science/chem/exps/KIO4_synth/i...

kadriver - 13-11-2012 at 13:36

Excellent - your website is very straight forward and easy to follow.

Can I substitute sodium bromide for potassium bromide and follow the same procedure as outlined on your website?

I need some relatively pure sodium bromate for some experiments.

I am going to order the Pt wires and glass tubing and duplicate your anode apparatus for the synthesis.

I have a piece of stainless steel metal strap from the hardware store that I can use for the cathode, and I have some potassium dichromate.

Thank you for the information - very helpful to me.

kadriver

kadriver - 13-11-2012 at 14:02

Also, I have a scrap platinum ring that I have been saving to refine the pure platinum from.

Do you think that this could serve as a suitable platinum anode for the bromate cell?

kadriver

woelen - 14-11-2012 at 01:15

The ring could be used as an anode, provided it is sufficiently pure platinum and you are able to completely encapsulate all connecting wiring in glass. You could make a cut in the ring and bend it such that a straight 'stick' is obtained and then solder a wire to this stick and melt the wire and the solder connection in glass. If you do not have a complete encapsulation of the wire and the solder point, then no (or only a small amount of) bromine is formed at the anode, then the wire and the solder point simply corrode as soon as power is applied to the cell.

Replacing KBr by NaBr can be done and leads to formation of bromate as well, but you will have a much harder time to make a pure product, free of bromide. Both NaBr and NaBrO3 are very soluble and are not easily separated. NaBrO3 also is somewhat hygroscopic, which adds to the difficulty of obtaining a nice pure product. That's why I made KBrO3. KBrO3 is soluble very well in hot water, but only moderately in cold water, while KBr is very soluble in cold water. This makes purification (separation from bromide) of the KBrO3 piece of cake.


[Edited on 14-11-12 by woelen]

kadriver - 14-11-2012 at 05:41

Great info, thanks for responding. Encapsulating the connections in glass tubing is absolutely brilliant.

If I can use the ring, then I can save about $60 as a 50mm piece of .5mm Pt wire cost just that, plus shipping.

I proved the ring by heating it to bright yellow (greater than red) and allowing it to cool back to room temp. The metal experienced no color change and looked as if it had never been touched with a flame after it cooled.

I have read that platinum and some other sister metals of the platinum group (excluding palladium) exhibit this quality.

Based on the information on your site, and chosing the Na instead of potassium; If I allowed the reaction to continue for greater than 6 hours, say doubling it to 12 hours, would this increase the amount of bromate formed, and decrease the amount of bromide contaminant?

Since both are very soluable, I understand that using this method will not provide a complete seperation of the bromide and bromate.

Thank you, this has all been very helpful.

kadriver

watson.fawkes - 14-11-2012 at 05:54

Quote: Originally posted by woelen  
you are able to completely encapsulate all connecting wiring in glass.
Use soda-lime glass for this purpose. It's got a coefficient of thermal expansion much more closely matched to Pt that does borosilicate glass. If you're using, say, copper wire, encapsulate as little of the wire as possible, since there's no thermal coefficient match there. You can run the wire inside a hollow tube without a problem, though; just don't try to melt the glass onto a long copper wire and expect it to hold. If you were using Pt wire, you'd seal on just a short section of the wire and put the power supply joint entirely inside the tube.

You'll also want a way of mechanically supporting the electrode. If you rely on the joint itself, you'll be putting extra mechanical strain on a joint that's already got some strain. It's already a little touchy to make a glass-tube to flat-metal seal. Treat it gingerly.

woelen - 14-11-2012 at 07:02

By letting the cell run for a longer time you may have a somewhat lower bromide content, but you never get zero bromide content. Even when some dichromate is present in the solution, you will have some back-reduction at the cathode. I think that no matter how long you do electrolysis in the cell, there always will remain a certain percentage of bromide. I do not know the numbers, but I expect a few percent at least.

One thing you could do is perform electrolysis of the cell and keep on electrolysing until hardly any bromine is formed at the anode and instead bubbles of oxygen are produced at the anode. If you have reached that point, then at most a few percent of the bromine is present as bromide, the rest will be present as bromate.

kadriver - 14-11-2012 at 08:41

Quote: Originally posted by woelen  


One thing you could do is perform electrolysis of the cell and keep on electrolysing until hardly any bromine is formed at the anode and instead bubbles of oxygen are produced at the anode. If you have reached that point, then at most a few percent of the bromine is present as bromide, the rest will be present as bromate.


This is what I was looking for - thank you woelen

kadriver

kadriver - 20-11-2012 at 04:57

woelen:

I have the sodium bromide, I am going to cut the Pt ring and straighten it out. Then, using some heat and a small hammer and an anvil, form one end of the ring into a thin round straight piece to facilitate encapsulation in the glass.

One question, is there an optimum size ration between the anode and the cathode? Should I use 1 to 1, or is there a better combination?

Also, is there an optimum cell size? I want to get about 100 grams of sodium bromate from the cell.

I was thinking a 600ml beaker with 400ml of saturated sodium bromine solution with a watch glass on top of the beaker.

I'll be doing the reaction in a fumehood.

Thank you,

kadriver

kadriver - 12-2-2013 at 00:04

Is there another solvent (other than water) that can be used to separate the bromate from the bromide?

Is there a non-polar solvent that will dissolve the bromate and not dissolve the bromide (or vis-versa)?

Kadriver

woelen - 12-2-2013 at 04:35

I do not know of an alternative for water, which is manageable without special apparatus.

Separating sodium bromate from sodium bromide is not very easy. For that reason I made potassium bromate, which is MUCH easier to separate from potassium bromide. You can use fractional crystallization from water, but the process is not really selective. Sodium bromate is less soluble than sodium bromide, but the difference is not so large that a single recrystallization almost completely eliminates the bromide from the crystals of bromate. Probably you need two or even three recrystallizations.

I have some commercial sodium bromate and this gives a faint yellow color when it is dissolved in dilute sulphuric acid. This is an indication of the presence of bromide. I made KBrO3 myself and when this is dissolved in dilute sulphuric acid, then the solution remains completely colorless, like pure water.

kadriver - 16-2-2013 at 05:27

Thanks woelen.

I will do the dilute sulfuric acid test on the bromate that I aquired to see if I get a color change as you described.

kadriver