Sciencemadness Discussion Board

Sulfuric acid from SO2 and FeCl3/CuCl2?

Gremory - 8-2-2020 at 12:59

According to the wikipedia article on sulfuric acid:

"Sulfuric acid can be produced in the laboratory by burning sulfur in air and dissolving the gas produced in a hydrogen peroxide solution.

SO2 + H2O2 → H2SO4
Or alternatively, with stirring, dissolving sulfur dioxide (any source) in an aqueous solution of a certain oxidizing metal salt such as copper (II) or iron (III) chloride:

2FeCl3 + 2H2O + SO2 → 2FeCl2 + H2SO4 + 2HCl
2CuCl2 + 2H2O + SO2 → 2CuCl + H2SO4 + 2HCl"

The H2SO4 from H2O2 makes sense, but I can't understand how the reactions with the oxidizing metal salts are useful. When the Sulfuric acid is produced, it should react with the iron/copper chlorides immediately to produce iron/copper sulfates and more hydrochloric acid.

Is this just another case of misinformation on the internet, or is there something I'm missing here, and could this be a feasible way to produce sulfuric acid from readily available ferric chloride?

Thank you for your time.

Abromination - 8-2-2020 at 13:10

NurdRage has a video on the metal chloride process and he determined that it wasn’t economically feasible. You would be better off by using an SO2 generator (burning sulfur is a terrible method, use sodium metabisulfite and acid) and bubbling it through concentrated hydrogen peroxide.
You could also make nitric acid with sodium bisulfate and a nitrate salt and bubble SO2 through it, giving you a much more concentrated solution. If you can though, just buy it as a drain cleaner.

Gremory - 9-2-2020 at 06:39

Thanks for pointing out the video, but I still think this might be useful (at least where I live), as buying sulfuric acid is practically impossible, and the maximum concentration of hydrogen peroxide available to the individual is 12% w/w. I don't understand why you think burning sulfur is a terrible method, as it certainly would be cheaper that the sodium metabisulfite/HCl method, so could you clarify what you mean?

Abromination - 9-2-2020 at 09:52

It is not cheaper then buying metabisulfite, and the production is much harder to control. The rate of gas flow itself is inconsistent. You are capable of concentrating hydrogen peroxide a bit by slow heat and evaporation (dont boil it) in a smooth glass beaker. I know this because I am also incapable of purchasing sulfuric acid in my area.
Also dont forget about the nitric acid method, it is quite simple.
Besides, metabisulfite is a useful chemical to have around anyways.

Gremory - 9-2-2020 at 12:58

Alright, you obviously know more than I do about this, so I'll go with the metabisulfite route. Is concentrating the H2O2 necessary, and if so, what temperature is the best to keep the solution at to minimise loss of H2O2? I would expect it wouldn't really matter, as after producing the sulfuric acid with dilute H2O2, a lot of water could be readily boiled off, with little loss of the acid, because of its very high boiling point.

Abromination - 9-2-2020 at 15:13

Quote: Originally posted by Gremory  
Alright, you obviously know more than I do about this, so I'll go with the metabisulfite route. Is concentrating the H2O2 necessary, and if so, what temperature is the best to keep the solution at to minimise loss of H2O2? I would expect it wouldn't really matter, as after producing the sulfuric acid with dilute H2O2, a lot of water could be readily boiled off, with little loss of the acid, because of its very high boiling point.

It isn't necessary to concentrate your peroxide, but I would recommend it. You may be fine with 10% peroxide as is. If you decide to concentrate it, keep it in a wide, very clean and smooth glass beaker. Do not boil it, this will cause decomposition. Heat it to around 50 or max 60 degrees Celsius. If you see bubbles being liberated, keep in mind that it is oxygen, not boiling. Its hard to concentrate it past 15-17 percent, and at this point it should be evident by visible decomposition. This can be boiled down after the reaction with SO2 (keep the peroxide cold!) and will give a higher yield proportional to your time and how much metabisulfite you have to use.