Sciencemadness Discussion Board

Reaction of Persulfates with Magnesium and other metals

Apos - 21-11-2023 at 16:39

Hello all!

I've recently gotten my hands on some Sodium Per(oxodi)sulfate (sold as PCB etchant) and have read up on a lot of interesting Persulfate chemistry, especially in regards to water treatment (seriously, check it out if that sounds interesting to you).

Being relatively new to chemistry, I'd like to ask you guys for help regarding the exact reaction occurring between Persulfates and Magnesium:

Under heating, Persulfates are reported to decompose to Sulfate ions, so does that mean it reacts the Magnesium to MgSO4? What about the, for example in Sodium Persulfate, remaining Sodium cation? Or does it oxidise the Magnesium to Magnesium oxide and itself decompose to Sodium sulfate?

Thanks for your help!

woelen - 22-11-2023 at 00:20

if you mix solid Mg with solid Na2S2O8, then the first main reaction will be

Mg + Na2S2O8 --> MgO + Na2S2O7 --> MgSO4 + Na2SO4

But I'm quite sure there will be further reduction. At high temperatures, which you can expect in the reaction of the solid materials, there will be further reactions, leading even to magnesium sulfide.

If you dissolve Na2S2O8 in water and add magnesium to that, then I expect the reaction to stop at sulfate:

Mg + S2O8(2-) --> Mg(2+) + 2 SO4(2-)

You get a mixed solution of magnesium sulfate and sodium sulfate.

There may be some side reaction. Solutions of Na2S2O8 tend to be a little acidic, because of decomposition of S2O8(2-) to oxygen and S2O7(2-). The latter leads to formation of HSO4(-) in water, which can react with Mg-metal to form some H2 and Mg(2=) ions.

Bedlasky - 22-11-2023 at 03:34

If you want some interesting experiments with persulfate, I recommend oxidation of Mn2+/Cr3+ in to MnO4-/(Cr2O7)2- in acidic solution. Reaction is catalyzed by Ag+. Another interesting one is oxidation of Ag+ in to Ag3+.


Apos - 22-11-2023 at 11:40

Quote: Originally posted by woelen  
if you mix solid Mg with solid Na2S2O8, then the first main reaction will be

Mg + Na2S2O8 --> MgO + Na2S2O7 --> MgSO4 + Na2SO4

But I'm quite sure there will be further reduction. At high temperatures, which you can expect in the reaction of the solid materials, there will be further reactions, leading even to magnesium sulfide.

If you dissolve Na2S2O8 in water and add magnesium to that, then I expect the reaction to stop at sulfate:

Mg + S2O8(2-) --> Mg(2+) + 2 SO4(2-)

You get a mixed solution of magnesium sulfate and sodium sulfate.

There may be some side reaction. Solutions of Na2S2O8 tend to be a little acidic, because of decomposition of S2O8(2-) to oxygen and S2O7(2-). The latter leads to formation of HSO4(-) in water, which can react with Mg-metal to form some H2 and Mg(2=) ions.


Thank you very much for the info! I actually got a lot of insight from the Persulfate experiments on your website :)

Would the Na2SO4 in the first reaction be further reduced to Na2S alongside the MgSO4 -> MgS? If not, does that mean the Na2SO4 is among the end products, or does it get reduced to a different compound? If it isn't too much of a bother and you happen to know the full reaction, I would be very grateful if you could post it here.

I hope I can get some 200+µm magnesium powder soon to test for the reaction products myself, but I sadly can't get any right now. I hope 200µm is coarse enough to slow the reaction down so much as to stop it from deflagrating like at under 100µm.

Thanks again for the help!

Apos - 22-11-2023 at 11:45

Quote: Originally posted by Bedlasky  
If you want some interesting experiments with persulfate, I recommend oxidation of Mn2+/Cr3+ in to MnO4-/(Cr2O7)2- in acidic solution. Reaction is catalyzed by Ag+. Another interesting one is oxidation of Ag+ in to Ag3+.




I've read about them before! Once I can get to it, I'll try them soon! Thank you for the recommendation :)