Hawkguy
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Potassium Persulfate
Hey, so today I was preparing about 5g of Potassium Persulfate, and things went up shit creek. So the original idea was (NH4)2S2O8 + 2KCl -> K2S2O8
+ 2NH4Cl.. This is the method I have already looked into, and it seems most people do that well enough without incident. Instead, what happened was
Ammonia gas and Chlorine were produced, and a*sf*cked me up when I checked on it 5 minutes later. Any idea what went wrong? The whole thing was done
at 10 degrees C btw.
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HeYBrO
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The chloride was oxidised to chlorine, and it sounds like the ammonium ion was some how deprotonated, how do you know both gasses were produced?
Smell? sight?
[Edited on 26-10-2014 by HeYBrO]
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blargish
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Here is a Youtube video of a guy performing the same procedure that you stated without incident...
https://www.youtube.com/watch?v=jN9tn1s88DI
I'm not sure what went wrong in your case
BLaRgISH
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unionised
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It's not a good idea to electrolyse solutions of ammonium chloride unless you actually want trouble.
You risk making chloramines and NCl3
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Hawkguy
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Quote: Originally posted by unionised  | It's not a good idea to electrolyse solutions of ammonium chloride unless you actually want trouble.
You risk making chloramines and NCl3 |
Ridiculously confused by that, all due respects and all. I don't believe saying I was doing electrolysis on anything at all (I'm assuming thats what
you were talking about.)
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blogfast25
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| Quote: Originally posted by HeYBrO | | The chloride was oxidised to chlorine, and it sounds like the ammonium ion was some how deprotonated, [...] |
S<sub>2</sub>O<sub>8</sub><sup>2-</sup> + 2 H<sup>+</sup> + 2 e<sup>-</sup> => 2
HSO<sub>4</sub><sup>-</sup>
The standard oxidation reduction potential is 2.1 V, about the same as permanganate.
The reaction requires H<sup>+</sup> but HSO<sub>4</sub><sup>-</sup> is a proton donor too, so it's not clear where
the ammonia is supposed to come from.
But he's working in far too high concentrations. That's a recipe for the potassium persulphate to be riddled with ammonium and chloride ions due to
occlusion. You shouldn't obtain such a thick paste.
[Edited on 26-10-2014 by blogfast25]
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woelen
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| Quote: Originally posted by Hawkguy | | Hey, so today I was preparing about 5g of Potassium Persulfate, and things went up shit creek. So the original idea was (NH4)2S2O8 + 2KCl -> K2S2O8
+ 2NH4Cl.. [...] |
Please describe exactly what you did in your experiment. I hardly can imagine that this does not work, unless your ammonium persulfate has
gone bad (it tends to absorb moisture and then it decomposes, giving O2 and NH4HSO4). K2S2O8 is only very sparingly soluble and KCl and (NH4)2S2O8 are
soluble quite well. The presence of acid may screw up things. The chloride then indeed can be oxidized to chlorine and that in turn can react with
ammonium ions, giving NCl3, N2 and more acid.
If I were you, I would proceed as follows:
- Dissolve some of your ammonium persulfate in water and add a small quantity of ammonia, until the solution is slightly alkaline. Some excess ammonia
does not hurt. Make the solution as concentrated as possible in ammonium persulfate. Heat somewhat to allow even higher concentration. Be sure that
the solution is slightly alkaline. Acidity is bad in this experiment!
- In a separate beaker, dissolve some KCl in warm water.
- Mix the two clear and colorless liquids and allow to cool down slowly.
With this, I am quite sure that you get crystals of K2S2O8.
In the above, heating must be marginal (to 50 C or so). Heating to boiling leads to decomposition of the persulfate, so just make things luke-warm.
[Edited on 27-10-14 by woelen]
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