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weiming1998
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Catalytic oxidation of sulfurous acid
I have tried to make sulfuric acid by bubbling sulfur dioxide through water. The process made sulfurous acid, by the reaction: H2O+SO2<==>H2SO3.
The sulfurous acid is slowly oxidized by air into sulfuric acid with the equation: 2H2SO3+O2====>2H2SO4. But the oxidation is very slow, even
with a large surface area, and it is often prone to decomposition into SO2 and H2O. Is there a catalyst for the oxidation of H2SO3, and if there is,
will catalysts for the oxidation of anhydrous SO2 work on sulfurous acid(Fe2O3, NO2, V2O5, etc) Also, how can the equilibrium be stopped from shifting
to the left?
Note: I know of the H2O2 method, but the H2O2 available at where I live is very dilute (3%-6%) and very expensive ($7 dollars for 100 ml of 6% H2O2!)
I also know the electrolysis method, but it is a waste of batteries for me, as I don't have an AC/DC converter.
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Pulverulescent
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The oxidation can be speeded up, somewhat, by bubbling dry O<sub>2</sub> in (at low temperature to minimise
SO<sub>2</sub>-loss)!
Ozone would be the ideal, but affordable, efficient ozone generators are pretty thin on the ground . . .
P
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weiming1998
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Yes, I do have an ozone generator that bubbles small amounts of ozone (400mg generated/hour) and air. I turned it on for 10 minutes. The yield
increased, but only very slightly. I guess I should try and bubble ozone for a few hours instead. Is there any other catalyst methods?
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LanthanumK
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Try addition of hydrogen peroxide. This reaction most likely occurs: H2SO3 + H2O2 -> H2SO4 + H2O
hibernating...
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Pulverulescent
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| Quote: | | Note: I know of the H2O2 method, but the H2O2 available at where I live is very dilute (3%-6%) |
You can get 35%H<sub>2</sub>O<sub>2</sub> here!
Bit pricey, though, and you'll need to boil the extra water off afterwards to get to 98% . . .
P
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AJKOER
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Here are some possible routes to oxidizing SO2 to make H2SO4:
1. Prepare SO2Cl2, a colorless fuming liquid. Sulfuryl chloride can be synthesized by combing SO2 and Cl2 in sunlight, or in the presence of camphor
or activated charcoal as a catalyst:
SO2 + Cl2 --Catalyst--> SO2Cl2
Adding water forms Chlorosulfuric acid and Hydrogen chloride:
SO2Cl2 + H2O --> HSO3Cl + HCl
Adding more water forms Sulfuric acid and Hydrogen chloride:
HSO3Cl + H2O --> H2SO4 + HCl
2. Prepare HOCl/Cl2O. This route takes time, but is cheap. Add a weak acid (vinegar) to the highest available Bleach available (but the cheap 6% would
also work, but requires more distillation to concentrate). This forms dilute HOCl which upon distilling off half of the solution will also double the
HOCl concentration. This is because most of the Cl2O and HOCl as vapor comes over first (see Watt's). Concentrated HOCl (30%) is unstable but will
oxidize S in water (or SO2) to H2SO4! Variations of this method employ Dichlorine mono-oxide. Cl2O can be prepared with some effort (and lab
equipment) by directly passing Cl2 over heated moist Na2CO3, or heated NaOH and collecting the gas in a small quantity of H2O or CCl4. The reaction
between Cl2O (or dry Ca(ClO)2 as it forms Cl2O with CO2 from the air) and dry Sulfur is explosive, but treating a thick Sulfur water suspension with
Cl2O (in essence making conc HOCl) cautiously should work.
Caution: Explosion hazard avoid high concentrations of Cl2O in CCl4, contact with organic compounds, heat, shock and/or light.
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Pulverulescent
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Dilute nitric acid is an excellent oxidiser but some (approximate) stoichiometry would be needed . . .
I should say I haven't tried it myself, so caution is advised!
Heating the solution in a fumehood (or downwind) would drive off any unreacted HNO<sub>3</sub>!
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AJKOER
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A well know reaction:
HIO3 + 3 H2SO3 --> HI + 3 H2SO4
upon heating, the HI should come across as vapor.
Iodic acid, HIO3, can be prepared by the slow reaction of Iodine with water:
I2 + H2O <----> HI + HIO
and very rapidly:
3 HIO ----> HIO3 + 2 HI
Bubbling air into the above solution:
4 HI + O2 --> 2 H2O + 2 I2
and the reaction cycles creating HIO3.
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plante1999
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Ad NO2 in the H2SO3 , this , with O2 will make H2SO4, this processe is called the lead chamber process.
I never asked for this.
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weiming1998
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I am not allowed to buy things off the internet, and it would be very difficult for me to combine SO2 and Cl together. I don not have a distillation
setup, so I can't distill the hypochlorous acid. Also, if I have nitric acid, why should I worry about getting sulfuric acid? Finally, the I2+H2O
method seems good, as I will be trying to generate some iodine from 600 grams of dried seaweed. But I don't think there would be more than a few
grams, and there is no supplier that will dare sell iodine. Also, I have no access to NO2. I tried to bubble chlorine through sulfurous acid before,
and the yields are pretty high, but when I concentrate it, even if I boil it from 500mls to 25 mls, it still didn't get any purer! I would guess the
ozone method is the most available to me right now. By the way, would Fe2O3 be a good catalyst?
[Edited on 16-1-2012 by weiming1998]
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plante1999
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Wath apparatus does you have for generating O3? Fe2O3 will disolve in H2SO4 so no it won't be a good catalist. If I was gessing , I would say cobalt
sulfate + O3 should oxidise realy fast H2SO3 to H2SO4.
[Edited on 16-1-2012 by plante1999]
[Edited on 16-1-2012 by plante1999]
I never asked for this.
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weiming1998
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Somehow, I have an ozone generator that my parents took from China. It produces mainly air with a little bit of ozone mixed in it. Anyway, I don't
think Fe2O3 will be dissolved very fast in very dilute H2SO4.
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Pulverulescent
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| Quote: | | I would say cobalt sulfate + O3 should oxidise realy fast H2SO3 to H2SO4. |
O<sub>3</sub> is just about the most effective oxidiser there is ─ why on earth would anyone want Co compounds in it, FFS? ( )
P
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BromicAcid
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http://www.sciencemadness.org/talk/viewthread.php?tid=6911&a...
There are two posts in this thread, one by me and one by Polverone regarding metal salt catalysis of SO2 solutions to give sulfuric acid. Check out
the links for more info.
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Sedit
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Mn sulfate seems like it might be of some use here.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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weiming1998
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Thank you, now I will try HClO and sulfur, then manganese sulfate.
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weiming1998
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I just tried sulfur+hypochlorous acid. Here's what happened:
50mls of white vinegar is poured into a flask.
About 5-10 grams of calcium hypochlorite is added. The mixture is left to react for 30 seconds. The liquid is then separated from the solid, unreacted
calcium hypochlorite and poured into a bottle. Sulfur is added in considerable amounts. The mixture has gotten warm and bubbling has started. The
sulfur is now moving around in the solution. Floating sulfur sinks down for a while, then floats back up. The bubbles are chlorine gas (I think)
because of what it smells like. Now, the mixture is acidic enough to react slightly with an iron wire, though it could just be the HCl that is formed
corroding the iron.
[Edited on 17-1-2012 by weiming1998]
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AJKOER
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You may be short on the acetic acid as if you are using Bleaching powder, it contains some Ca(OH)2 (and CaCl2 hydrate) as well.
Also, you can start the oxidation chain via HOCl (created per the Acetic acid + Ca(ClO)2 ) not from the very beginning at Sulfur, but at H2SO3 (if you
have so):
S + 2 HOCl --> SO2 + 2 HCl
SO2 + H2O + HOCl --> H2SO4 + HCl
Note, the reaction releases HCl as well so if insufficient Acetic acid, some Cl2 may be formed.
You can also employ (with precautions) H2S in water in place of H2SO3. Hydrogen sulfide can prepared per the reaction of heating Al + S (thermite in
nature so do not attempt to heat the whole mixture; use very small quantities as the reaction is very exothermic capable of melting thru steel at
1,100 C) and then adding water to the Aluminum Sulphide (which is very sensitive to moisture forming H2S on contact). I would design the experiment
so that the HOCl is available in a closed reaction chamber with the Al2S3 and water (that produces H2S and Al(OH)3 ). Note, Aluminum hydroxide does
not readily react with HOCl. Caution, H2S is very toxic and will numb the senses (allowing a fatal dose via inhalation or skin exposure) hence the
closed vessel approach. Nevertheless, take precautions and certainly do outdoors if considering this approach.
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AJKOER
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OK, I just noticed a major problem. You should have created the HOCl by reacting Ca(OCl)2 with H2CO3 and not Acetic acid (as you did not distill to
get pure HOCl). As a result, you have some Calcium acetate (a soluble ionic salt) in solution. So free H2SO3 or H2SO4 could react with it to form the
insoluble CaSO4.
Try again, use pure carbonated water, and filter out the CaCO3.
Also, the process with dilute HOCl should be slow (a gradual rise in the solutions pH with time).
Do not use Fe to test solution strength as even dilute HOCl attacks iron.
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Endimion17
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Maybe you should check your premise first. There's no such thing as sulphurous acid being made by blowing sulphur(IV) oxide in water. The
H<sub>2</sub>SO<sub>3</sub> molecule doesn't exist in water.
Burning sulphur and stuffing the produced fumes in the water produces a solution of SO<sub>2</sub> and sulphuric acid (from traces of
SO<sub>3</sub> made by the reaction of hot SO<sub>2</sub> with atmospheric oxygen).
Bubbling sulphur(IV) oxide through water doesn't produce sulphurous acid.
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Pulverulescent
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| Quote: | | Maybe you should check your premise first. There's no such thing as sulphurous acid being made by blowing sulphur(IV) oxide in water.
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LoL! 'Been reading the 'ever trustworthy' wiki again, have we??? 
P
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AndersHoveland
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It was my understanding that SO2 in water behaves analogously to CO2 in water, which is to say that the reason for the high solubilities is the
equilibrium with their respective acids, H2SO3 and H2CO3.
[Edited on 17-1-2012 by AndersHoveland]
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ScienceSquirrel
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A solution of sulphur dioxide in water contains sulphur dioxide, bisulphite anions and solvated protons.
It is effectively a solution of sulphurous acid in so far as it forms salts with bases, acts as an acid towards indicators, it is a strong reducing
agent, etc.
Some of chemistry is about sticking labels on things, some labels are better than others but very few of them really describe the underlying state of
affairs.
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AndersHoveland
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Quote: Originally posted by ScienceSquirrel  | | Some of chemistry is about sticking labels on things, some labels are better than others but very few of them really describe the underlying state of
affairs. |
Yes, but chemists almost never refer to aqueous SH2 solutions as "hydrosulfuric acid". It is always referred to as "hydrogen sulfide". Similarly, when
zinc chloride is dissolved in ether, it should technically be referred to as "zinc dichloride adduct", but chemists just do not do this.
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weiming1998
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| Quote: Originally posted by AJKOER | OK, I just noticed a major problem. You should have created the HOCl by reacting Ca(OCl)2 with H2CO3 and not Acetic acid (as you did not distill to
get pure HOCl). As a result, you have some Calcium acetate (a soluble ionic salt) in solution. So free H2SO3 or H2SO4 could react with it to form the
insoluble CaSO4.
Try again, use pure carbonated water, and filter out the CaCO3.
Also, the process with dilute HOCl should be slow (a gradual rise in the solutions pH with time).
Do not use Fe to test solution strength as even dilute HOCl attacks iron. |
Ok, I will try this with carbonated water instead.
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