Sciencemadness Discussion Board

Sulfuric acid from sulfur dioxide and nitric acid.

Chemgineer - 6-12-2021 at 15:12

I had a go at following Nurdrage's procedure for making sulphuric acid.

I made a sulphur dioxide generator using 50g sodium metabilsulfite 50ml distilled water and then dripping 100ml of 20% hydrochloric acid (brick cleaner) via a pressure equalised addition funnel.

I fed the sulphur dioxide through tube and bubbled it through a 46% solution of nitric acid which I previously produced by reacting sodium bisulfate and magnesium nitrate.

I got plenty of nitrogen dioxide released from the nitric acid and it went a dark green colour which confused me.

Thinking it would clear up I ran the gas generator for a second time which released more nitrogen dioxide but still resulted in a green solution.

If I test the solution with a ph test strip the vapours coming off turn it red but dipping in the solution seems to bleach the paper either that or it's a ph of 6.

Do I maybe need to keep pushing sulphur dioxide through it or have I got a contaminant from somewhere producing my green colour? I know nitric acid and copper would produce green but I can't think of any copper in my setup.

I thought this might be an easier way to produce clean sulphuric acid rather than using copper sulfate but it's not looking like it so far.

[Edited on 6-12-2021 by Chemgineer]

BauArf56 - 7-12-2021 at 04:17

Nitric acid and sulfur dioxide can make nitrosylsulfuric acid, which wikipedia claims to be pale yellow. Maybe your color is given by this compound.

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Amos - 7-12-2021 at 06:25

You prepared nitric acid from sodium bisulfate and magnesium nitrate? As in, you dry-distilled a mixture of the two, or distilled an aqueous solution of the two, or what?

Since you're doing aqueous chemistry, you're going to see nitrogen dioxide reacting with water to form nitrous acid, which is blue. Nitrogen dioxide dissolved in nitric acid gives a yellow color as well; so I think you're seeing the result of multiple nitrogen oxides and also perhaps nitrosylsulfuric acid. Simply refluxing the mixture for a bit will destroy nitrous acid since it's thermally unstable, so see if that removes the greenish color. This would also boil off some, but not all of the dissolved gases while leaving sulfuric acid since it's non-volatile. You'll probably end up doing this anyway to concentrate your sulfuric acid at the end.

One more thing! All that nitrogen dioxide you're generating is useful, and if you want to you can re-capture it by bubbling the product gases into dilute hydrogen peroxide. This would give you a mixed dilute solution of sulfuric acid(from leftover sulfur dioxide) and nitric acid; You could recycle this back into your reaction chamber to pass more sulfur dioxide into it, or use this weak mixture of acids to dissolve metals, or any number of things. It may become worthwhile if you're doing this reaction a lot or on a large scale.

Best of luck! It's sort of an unconventional way to obtain sulfuric acid since nitric acid is usually the harder one to get, but everyone has access to different supplies.

Chemgineer - 7-12-2021 at 07:46

Thanks for the detailed reply, my nitric acid was from a dry distillation (not anhydrous though and magnesium nitrate holds plenty of water) and resulted in 43% nitric acid according to the specific gravity.

Nitric acid I can make quite readily but producing good quality sulphuric acid has been a struggle, i've electrolysed copper sulfate before and boiled it down to 93% but it keeps dropping white deposits out of solution over time. So I figured the above might be cleaner as the nitric acid has been distilled and the sulphur dioxide is gaseous.

I'll have a go at heating it to just over 100 deg C and see what happens.

Chemgineer - 7-12-2021 at 13:12

Quote: Originally posted by Amos  
You prepared nitric acid from sodium bisulfate and magnesium nitrate? As in, you dry-distilled a mixture of the two, or distilled an aqueous solution of the two, or what?

Since you're doing aqueous chemistry, you're going to see nitrogen dioxide reacting with water to form nitrous acid, which is blue. Nitrogen dioxide dissolved in nitric acid gives a yellow color as well; so I think you're seeing the result of multiple nitrogen oxides and also perhaps nitrosylsulfuric acid. Simply refluxing the mixture for a bit will destroy nitrous acid since it's thermally unstable, so see if that removes the greenish color. This would also boil off some, but not all of the dissolved gases while leaving sulfuric acid since it's non-volatile. You'll probably end up doing this anyway to concentrate your sulfuric acid at the end.

One more thing! All that nitrogen dioxide you're generating is useful, and if you want to you can re-capture it by bubbling the product gases into dilute hydrogen peroxide. This would give you a mixed dilute solution of sulfuric acid(from leftover sulfur dioxide) and nitric acid; You could recycle this back into your reaction chamber to pass more sulfur dioxide into it, or use this weak mixture of acids to dissolve metals, or any number of things. It may become worthwhile if you're doing this reaction a lot or on a large scale.

Best of luck! It's sort of an unconventional way to obtain sulfuric acid since nitric acid is usually the harder one to get, but everyone has access to different supplies.


Ok heating it has released nitrogen dioxide and the solution is now yellow, it seems you were correct. I guess I just need to heat it above 121 deg C now to boil off remaining g nitric acid leaving sulphuric acid behind.

[Edited on 7-12-2021 by Chemgineer]

zerodan - 7-12-2021 at 17:07

Quote: Originally posted by Chemgineer  
Quote: Originally posted by Amos  
You prepared nitric acid from sodium bisulfate and magnesium nitrate? As in, you dry-distilled a mixture of the two, or distilled an aqueous solution of the two, or what?

Since you're doing aqueous chemistry, you're going to see nitrogen dioxide reacting with water to form nitrous acid, which is blue. Nitrogen dioxide dissolved in nitric acid gives a yellow color as well; so I think you're seeing the result of multiple nitrogen oxides and also perhaps nitrosylsulfuric acid. Simply refluxing the mixture for a bit will destroy nitrous acid since it's thermally unstable, so see if that removes the greenish color. This would also boil off some, but not all of the dissolved gases while leaving sulfuric acid since it's non-volatile. You'll probably end up doing this anyway to concentrate your sulfuric acid at the end.

One more thing! All that nitrogen dioxide you're generating is useful, and if you want to you can re-capture it by bubbling the product gases into dilute hydrogen peroxide. This would give you a mixed dilute solution of sulfuric acid(from leftover sulfur dioxide) and nitric acid; You could recycle this back into your reaction chamber to pass more sulfur dioxide into it, or use this weak mixture of acids to dissolve metals, or any number of things. It may become worthwhile if you're doing this reaction a lot or on a large scale.

Best of luck! It's sort of an unconventional way to obtain sulfuric acid since nitric acid is usually the harder one to get, but everyone has access to different supplies.


Ok heating it has released nitrogen dioxide and the solution is now yellow, it seems you were correct. I guess I just need to heat it above 121 deg C now to boil off remaining g nitric acid leaving sulphuric acid behind.

[Edited on 7-12-2021 by Chemgineer]

Do you have access to elemental sulfur? You should try SO2 from burning sulfur, granted it's less convenient but still workable and hopefully more pure.
Given that you mentioned using HCl from brick cleaning agent, I suspected that maybe some of the Fe(2+) made it over with the vapor as it's a common additive.

Chemgineer - 7-12-2021 at 19:12

I have several kg of sulphur but it's a bit more of a challenge to produce sulphur dioxide from it reliably.

AJKOER - 22-12-2021 at 08:37

A chemically interesting path here for the preparation of H2SO4 is from the action of HOCl (in excess) on S (or SO2) mentioned in Watt's Dictionary of Chemistry. Mixed product of HCl and H2SO4, albeit, the HCl can be 1st removed by distillation.

If you have prepared HOCl from mixing CaCl2 + NaOCl (aq)+ CO2, followed by cooling and allowing the white suspension to settle. Expect a short shelf life for the hypochlorous acid, so react with sulfur in short order. Note: distilling half of your dilute HOCl off, results in a near doubling of its concentration as the volatile Cl2O escapes off early and re-dissolves in the condenser.

I surmise using SO2 in place of CO2 may be manageable here (note: no strong acids as much chlorine gas may be formed and the absolute worst case, per my experience, occurs with oxalic acid, H2C2O4 with an overwhelming amount of CO2 mixed with Cl2 in a violent exothermic reaction even when I attempted it in small amounts).

[Edited on 22-12-2021 by AJKOER]

Amos - 22-12-2021 at 14:32

Quote: Originally posted by Chemgineer  
I have several kg of sulphur but it's a bit more of a challenge to produce sulphur dioxide from it reliably.


All you must do is pile it up outdoors and set it on fire at the top of the pile with a lighter; you can also cast it into candles. Then use a vacuum to pull it through the system and finally pass the exiting gas through a wash bottle of dilute hydrogen peroxide(for extra sulfuric acid production) or another oxidizer/base. The problem is that sulfur itself will also vaporize and get into your sulfur dioxide gas; I propose using a makeshift cooling tower out of something cheap you can sacrifice, like a long piece of aluminium dryer vent, tapered to a point with tubing at the end. That would give hot sulfur vapor time and surface area to deposit as a solid, preventing your tubing from clogging. You can also just pass sulfur dioxide directly into dilute peroxide and merely boil or use a combination of boiling and evaporation to concentrate it. Whatever you want to do, you're certainly doing okay right now.

Try to ignore AJKOER. Their answer to every problem is a convoluted pathway involving bleach. I really don't know why.

[Edited on 12-22-2021 by Amos]

AJKOER - 22-12-2021 at 18:59

Amos:

Here is a reference per Page 2 at https://www.hach.com/cms-portals/hach_com/cms/documents/pdf/...

H2SO3 + HOCl -> H2SO4 + HCl

Here is my orginal Watts reference found on the right side middle of Page 16 at https://www.google.com/books/edition/Watts_Dictionary_of_Che... Note: Watts also claims the reaction proceeds with dilute HOCl. Further, if HOCl breaks down to HCl which results in any free Cl2, the reaction with SO2 forms a compound that reacts water to again liberate HCl and H2SO4 (so, the chemistry is affirnative).

And, yes HOCl is easily and inexpensively prepared from chlorine disinfecting bleach, unlike this threads idea of employing more valuable HNO3 further liberating problematic NO2 gas.

You should also be aware, there is much work in the area of Fenton (and Fenton-like) chemistry based on H2O2 with Fe ions (or H2O2 with non-Fe ions). There also a related chemistry, generally faster associated with HOCl in place of H2O2 referred to as Fenton-type reactions again with associated important radical formation. Fenton-type reactions can also be based on HNO2,...., in place of H2O2.

If one could use a cathode of graphite in place of platinum or gold, why would you not? The same argument applies here.

Finally, adding CO2 to NaOCl will not liberate chlorine. If worried, use an excess of NaOCl so if any Cl2 is formed, it just creates more HOCl.
Also, never attempt to concentrate HOCl over 20% (safety/stability issues).

Please ignore AMOS, albeit, I know he means well.

[Edited on 23-12-2021 by AJKOER]

chloric1 - 5-1-2025 at 18:53

Quote: Originally posted by AJKOER  
Amos:

Here is a reference per Page 2 at https://www.hach.com/cms-portals/hach_com/cms/documents/pdf/...

H2SO3 + HOCl -> H2SO4 + HCl

Here is my orginal Watts reference found on the right side middle of Page 16 at https://www.google.com/books/edition/Watts_Dictionary_of_Che...


Note: Watts also claims the reaction proceeds with dilute HOCl. Further, if HOCl breaks down to HCl which results in any free Cl2, the reaction with SO2 forms a compound that reacts water to again liberate HCl and H2SO4 (so, the chemistry is affirnative).

And, yes HOCl is easily and inexpensively prepared from chlorine disinfecting bleach, unlike this threads idea of employing more valuable HNO3 further liberating problematic NO2 gas.

You should also be aware, there is much work in the area of Fenton (and Fenton-like) chemistry based on H2O2 with Fe ions (or H2O2 with non-Fe ions). There also a related chemistry, generally faster associated with HOCl in place of H2O2 referred to as Fenton-type reactions again with associated important radical formation. Fenton-type reactions can also be based on HNO2,...., in place of H2O2.

If one could use a cathode of graphite in place of platinum or gold, why would you not? The same argument applies here.

Finally, adding CO2 to NaOCl will not liberate chlorine. If worried, use an excess of NaOCl so if any Cl2 is formed, it just creates more HOCl.
Also, never attempt to concentrate HOCl over 20% (safety/stability issues).

Please ignore AMOS, albeit, I know he means well.

[Edited on 23-12-2021 by AJKOER]


I’m not going to knock anyone for messing with chlorine or hypochlorites. I would hardly think big brother is going to take away this source because of wide application in disinfectants. It’s cheap and a very effective oxidizer. In some cases more effective than specialty oxidizers like permanganate. Also, it’s not like hydrogen peroxide which sometimes is a reducing agent at alkaline pH.