ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
Strange colors during hydrohalic acid syntheses
When I make hydrobromic acid and distill it out of solution, it is colored brownish-red, but no free bromine is observed on the bottom of the flask. I
think it's the tribromide ion in action.
Now when I do the same with hydrochloric acid, the boiling solution turns yellow! What is this, trichloride?
And if we had glassware coated with diamond and could distill HF the same way, what the color would be? Pale yellow?
[Edited on 11-12-2015 by ave369]
Smells like ammonia....
|
|
|
shivam
Harmless
Posts: 28
Registered: 26-10-2015
Location: GJ, India
Member Is Offline
Mood: Curious
|
|
While making Hydrobromic acid (or Hydrochloric acid as well), If the sulfuric acid is too concentrated, it will further oxidize the Hydrobromic acid
to bromine, hence the brownish red solution.
A few of these side reactions can happen through a few different ways:
2HBr + H2SO4 --> Br2 + SO2 + 2H2O
6HBr + H2SO4 --> 3Br2 + S + 4H2O
8HBr + H2SO4 --> 4Br2 + H2S + 4H2O
The amount of free bromine formed is not usually so much that it can form separate bromine layer at bottom. A little amount of bromine is readily
soluble in aqueous media.
During distillation, bromine comes over at much lower temperature than Hydrobromic acid, so contamination of bromine in distillate is inevitable
(unless you do a precise fractional distillation)
The key is to avoid using too much concentrated sulfuric acid and keeping temperature under control..
Use sulfuric acid that is a bit more diluted down. Having to remove more water afterwards through distillation is always more welcomed than poor
quality product.
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
Try some less hazardous operations until you understand basics and are familiar with techniques. All the shit about LAH comes from workers not trained
in chemistry.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
I do not use concentrated sulfuric acid for this. Standard battery acid, 36%. And my hydrobromic acid is clear as water, not even slightly yellow. Try
to presume less when you want to sound pedantic. We in Russia have a good saying: "All telepaths are on a leave", said to someone who behaves like
they are a telepath.
[Edited on 12-12-2015 by ave369]
Smells like ammonia....
|
|
|
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
Quote: Originally posted by chemrox  | | Try some less hazardous operations until you understand basics and are familiar with techniques. All the shit about LAH comes from workers not trained
in chemistry. |
Why this answer? Please be helpful, or do not answer at all. Your answer is the best way to
put off people and kill their interest in chemistry (or science in general) 
There is nothing wrong with the question of ave369, he just wonders what causes these colors he observes and does not show any evidence of doing
stupid or dangerous things without any understanding.
|
|
|
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
In the case of HBr, I think that the color is due to formation of some free bromine, which indeed remains in solution as Br3(-) when the concentration
of bromide is high. I myself once made some 40% HBr and this also turned yellow/brown. I believe this is due to oxidation by oxygen from air. Only a
small amount of free bromine can give a noticeable color.
With HCl I also noticed the formation of a pale yellow/green color, but on distillation of 22% HCl I obtained a perfectly colorless solution. I did
this by distilling hardware store 30% HCl. I diluted this to 22% or so with boiled tap water and then I distilled over appr. 90% of the liquid. The
liquid in the receiver was perfectly colorless and I use that sample of HCl for experiments where I want to be sure that no metal ions are in
solution. The remaining 10% of liquid was deep yellow and I discarded that.
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
At last, Woelen, the true scientist, not a snarker. I've got the same results as you. Maybe you answer the question where does the yellow-green come
when I distill HCl (az.) from 36% sulfuric and table salt? Is it truly trichloride, or just a solution of chlorine?
And I'm a SHE, the last time! I wonder why Polverone ignores my request for the custom title "Eastern European Lady of Mad Science" that would stop
gender confusion once and for all. Maybe you, woelen, can do that?
[Edited on 12-12-2015 by ave369]
Smells like ammonia....
|
|
|
shivam
Harmless
Posts: 28
Registered: 26-10-2015
Location: GJ, India
Member Is Offline
Mood: Curious
|
|
Okay ave369. Sorry for trying to help..
Didn't mean to come off as pedantic....
(please understand that people learn things with time, they grow into it...which is what i am doing --- and enjoying!)
SIGH...Good day! again Sorry for wasting your time..
[Edited on 12-12-2015 by shivam]
|
|
|
Amos
International Hazard
Posts: 1406
Registered: 25-3-2014
Location: Yes
Member Is Offline
Mood: No
|
|
| Quote: Originally posted by shivam | Okay ave369. Sorry for trying to help..
Didn't mean to come off as pedantic....
(please understand that people learn things with time, they grow into it...which is what i am doing --- and enjoying!)
SIGH...Good day! again Sorry for wasting your time..
[Edited on 12-12-2015 by shivam] |
I don't think she was talking to you about being pedantic; you were nothing but informative. I think the quote was directed at chemrox.
|
|
|
Amos
International Hazard
Posts: 1406
Registered: 25-3-2014
Location: Yes
Member Is Offline
Mood: No
|
|
| Quote: Originally posted by ave369 | where does the yellow-green come when I distill HCl (az.) from 36% sulfuric and table salt?
[Edited on 12-12-2015 by ave369] |
I can't speak about Russian table salt necessarily, but a common additive to table salt over here is a small amount of potassium or sodium
ferrocyanide, which will react with acids to give iron(II) chloride(pale green, yellowing as oxidation takes effect) as well as a small amount of
cyanide, which would be harmless in such a low concentration so long as your distillation receiver isn't your mouth.
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
I was specially buying pure table salt from Iletsk. It surely did not contain any anti-blobbing agents, because it was in huge blobs.
Smells like ammonia....
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
