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Here is how I was able to make sulfuric acid.

A membrane cell was made by placing a earthen clay pot in a larger vessel.

1.Make concentrated solution of potash alum. 2.Pour alum sol into both sides of the cell. 4. Using carbon electrodes applied a voltage of 14V.

The cell was run for 4-5 hr. Sulfuric acid was formed on the anode, and potassium and al hydroxide was formed on the cathode side. Tested with sodium bicarbonate to give of effervescence. No other tests were done, but what other acid can form if not sulfuric acid?

I am planning to repeat it to increase the yields, like substituting alum for other sulphate salts, thinner membrane, adding hydrogen peroxide on the anode side.

What else can I do to improve the yields?

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  • $\begingroup$ All solutions of sulfates will produce sulfuric acid in your cell. At the anode (positive pole), the electrolysis will produce $\ce{H2O -> O2 + 4 H+ + 4 e-}$. So the solution becomes acidic, due to $\ce{H2SO4}$ appearing in solution. But it contains more of the original sulfate. At the cathode, the reaction will be $\ce{2 H2O + 2 e- -> H2 + 2 OH-}$. So the cathodic solution becomes basic. The only way of improving the yield is to increase the duration of the electrolysis. Anyway you will never obtain pure sulfuric acid. You will always obtain a mixture sulfate + sulfuric acid. $\endgroup$
    – Maurice
    Jan 7, 2023 at 17:51
  • $\begingroup$ Ok so I have to distill it then? Also I did this a long time back and I think I only kept the sulfate solution on the cathode side only, the other side had distilled water.The SO4(2-) must have traversed the membrane to the other side. Have to repeat if this was what I had done. $\endgroup$
    – The Entity
    Jan 7, 2023 at 18:00
  • $\begingroup$ If one of the side is pure water, no current will flow through the cell. Pure water does not conduct electricity. $\endgroup$
    – Maurice
    Jan 7, 2023 at 20:29
  • $\begingroup$ Distillation is no use for purifying sulfuric acid solution. Sulfuric acid is not volatil. Heating such a solution will simply eliminate water. Sulfate and sulfuric acid will not be separated, and will remain mixed in the flask. $\endgroup$
    – Maurice
    Jan 7, 2023 at 20:32
  • $\begingroup$ ok ya right its bp is higher than water, can hydrogen peroxide improve the yields? $\endgroup$
    – The Entity
    Jan 7, 2023 at 21:08

1 Answer 1

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You may want to find a gold and silver refiner who has aqueous Copper Sulfate as a waste product. Your reactions become:

$$\ce{Cathode: 2Cu++ + 4e- -> 2 Cu metal + 0.34 V}$$

$$\ce{Anode: 2H2O -> 4H+ + 4e- + O2 gas - 1.23 V}$$

Valuable copper metal is produced before:

$$\ce{Cathode: 4 H+ + 4e- -> 2 H2 gas + 0.00 V}$$

Observation of H2 gas at Cathode would indicate reaction completion. Copper metal helps pay for the process. Dilute sulfuric acid can be concentrated by removing water.

Aluminum sulfate may not be the best as a starting material:

$$\ce{Cathode: Al+++ + 3 e- -> Al metal - 1.66 V}$$


Al +++ will not reduce before aqueous H+, or even water inself: $$\ce{Cathode: 2H2O + 2 e- -> H2 + 2 OH- - 0.83 V}$$

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    $\begingroup$ Metallic aluminum is never produced by electrolysis in aqueous solution. NEVER ! It is not a question of acidity ! Pure water reacts with metallic aluminum, whatever its pH. Metallic aluminum is produced by electrolysis in an anhydrous solvent (usually cryolithe) $\endgroup$
    – Maurice
    Jan 8, 2023 at 10:00
  • $\begingroup$ @Maurice edited for easier reading. $\endgroup$ Jan 8, 2023 at 15:21

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