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Author: Subject: Bromine salt testing reagent
bismuthate
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[*] posted on 19-3-2014 at 15:28
Bromine salt testing reagent


So lately I've been trying to figure out a way to detect inorganic bromine salts (bromides, bromates, bromites ect). I came up with the idea of testing for bromides by the use of copper sulfate dissolved in moderately concentrated sulfuric acid. The reaction of the sulfuric acid with the bromide would make HBr which would then react with the CuSO4 to form this complex http://woelen.homescience.net/science/chem/exps/copper_halog...
which I believe would not revert back to the blue CuSO4 solution because the H2SO4 would serve as a dehydrating agent.
I can't test this myself because I don't have acess to any decent sulfuric acid(mine's purple). Would this work or am I missing the obvious.
EDIT Oh yeah.. sorry if this belongs in beginings.

[Edited on 19-3-2014 by bismuthate]




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[*] posted on 19-3-2014 at 15:40


If you add MnO2 and some CCl4, you'll see bromine dissolving in the organic layer.



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bismuthate
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[*] posted on 19-3-2014 at 15:56


Oh I never thought of that, but I'm not trying to detect bromine I just wanted to try to come up with a new cheap way to do it (and I think it should work at pretty low concentrations). I love to do analytical chemistry.
Also if this works I would add SO2 to the mixture so that it would reduce bromates and other oxoanions allowing them to be detected too.

[Edited on 20-3-2014 by bismuthate]




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[*] posted on 2-2-2015 at 03:25


Is there a way to (sort of quickly/easily) test a (potassium) salt to determine whether it's a bromide or a bromate?
I found a bottle with a double label :s
The name-tag says Potassium Bromate but the formula on the back says KBr :/
So now I'm confused..

EDIT: Nevermind. Bubbling chlorine through the solution clearly indicated that it was a bromide salt(formation of bromine).

[Edited on 2-2-2015 by Jylliana]




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[*] posted on 2-2-2015 at 05:11


Add some of the solid to 30% HCl (take a small spatula full of solid and add this to appr. 2 ml 30% HCl in a test tube). If it is KBrO3, then it fizzles (the bubbles being a mix of Cl2 and BrCl) and the liquid becomes yellow, if it is KBr, then nothing happens, it just slowly dissolves.

Another easy test is to dissolve a small spatula full of solid in 2 ml of dilute H2SO4 (e.g. 15% H2SO4) and then add a tiny pinch of solid sodium sulfite or sodium bisulfite. If it is KBrO3, then quite a lot of bromine is formed and the liquid turns orange, if it is KBr, then the sulfite dissolves and you can smell the SO2 and the liquid remains colorless. Be sure to have excess KBr/KBrO3 relative to the sulfite.

What did the label say? In 'potjeslatijn' (I don't know how to call this labelling language otherwise), the name "kalium bromatum" stands for potassium bromide and "kalium chloratum" stands for potassium chloride. This is very confusing. Fortunately, these old-fashioned names are hardly used anymore.


[Edited on 2-2-15 by woelen]




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[*] posted on 2-2-2015 at 05:55


My former colleague stuck a label on it with

[ Potassium bromate, KBr. ] written in her own handwriting.

So one of them had to be wrong.
The original label had been ripped off.

Do bromate salts also form bromine with chlorine gas bubbled through it, like I described before?
I think not, but I'm not sure..



[Edited on 2-2-2015 by Jylliana]




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[*] posted on 2-2-2015 at 08:04


@ Bismuthinate

Have you checked out Vogel's textbook of semimicro analysis or Feigl & Anger Spot tests in inorganic analysis. They both have lots of tests to discriminate between chloride/bromide/iodide and the oxyanion analogs. Both books can be downloaded if you search the internet a bit. If you can't find them I can post copies somewhere. If you are interested in analysis they are "must haves".

One test I like because it works on exceedingly small mineral grains is filter paper soaked in dilute Na fluorescein dye. It is held over the mineral grain which has been mixed with MnO2 and strong (>25%) H2SO4. The Br fumes cause the paper to turn pink chlorine doesn't react for some reason. Iodide gives a slightly deeper colour. This test can be modified to work on a microscope slide, you just need a small spacer (a plastic ring 2mm deep and about 15mm ID) to stop the paper touching the drop.
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[*] posted on 2-2-2015 at 11:38


If you can convert the bromine salt to free bromine any way I'm sure there is a specific test for bromine based on its reaction with fluorescein, converting it from yellow fluorescein to orenga red dibromofluorescein.
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[*] posted on 2-2-2015 at 12:24


Quote: Originally posted by Jylliana  
[...]Do bromate salts also form bromine with chlorine gas bubbled through it, like I described before?
I think not, but I'm not sure..
You're right, chlorine does not release Br2 from bromate.
Bromate on the other hand can convert chlorine from chloride, itself being converted to BrCl. At very high concentration of acid, the reaction is as follows:

6H(+) + BrO3(-) + 5Cl(-) --> 2Cl2 + BrCl + 3H2O

The Cl2 and BrCl are gases and bubble out of solution. If you have KBrO3 or NaBrO3 and conc. HCl then just try this reaction in a test tube. You'll see another colored gas. BrCl is bright golden yellow and its color totally overwhelms the faint color of the Cl2 produced as well.

Here is a picture of fairly pure BrCl, which I made by reacting dried Cl2 and Br2 directly (only the picture is mine, the text is written by someone else):

https://en.wikipedia.org/wiki/Bromine_monochloride




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[*] posted on 6-2-2015 at 17:48


If one gets points for orginality or just the complex, a possible new test to detect perhaps even small amounts of salts containing bromine could be performed by treating a subect salt to a known quantity of both chlorine and ozone in the presence strong uv light, which in the event of the liberation of any bromine is expected to serve as a very effective catalyst for the conversion of the ozone to oxygen:

Br2 + uv --> Br + Br

Cl2 + uv --> Cl + Cl

Br + O3 --> BrO + O2

Cl + O3 --> ClO + O2

BrO + ClO --> Br + Cl + O2

One then tests for how rapidly O3 is depleted, for example, by a failed starch/iodide test, or the failure to produce a color change (to a steel blue) from the normal action of ozone on silver metal. Chlorine will by itself eventually destroy the ozone, but not as rapidly as by the above cycle which is largely attributed as the cause of the current hole in the ozone layer on earth.
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