Home Production of Copper Sulfate

Electrolysing Aqueous Magnesium Sulphate with 
Copper Electrodes to Produce Cuprous Sulphate

Andrew Spangler

Performed January 26, 2013

Purpose: To determine the possibility of producing copper sulphate through electrolysis of Aqueous magnesium sulphate with copper electrodes.

Hypothesis: If I electrolyse an aqueous solution of magnesium sulphate with two copper electrodes, then I will produce copper sulphate(aq), copper oxide(s), copper hydroxide(s), magnesium oxide(aq)*, magnesium hydroxide(s), sulphuric acid(aq), and magnesium(s)**.

Theory Supporting: the electrolysis of aqueous magnesium sulphate creates one diatomic hydrogen molecule and negatively charged hydroxide ions at the cathode. hydroxide ions have been shown to be have a higher reactivity than sulfite ions meaning that they will be more reactive toward the magnesium oxide and leave the sulfite ions to bond with the copper. Some hydroxide ions will react with the copper sulphate ions to produce copper hydroxide and the remaining sulphate ions will react with the hydrogen produced at the cathode to produce sulphuric acid. Finally, the copper ions will react with the oxygen produced at the sacrificial anode to produce copper oxide. All static products of this are insoluble except the copper sulphate and magnesium oxide* meaning that the resulting solution may be filtered and have aqueous magnesium sulphate and copper sulphate be the final product.

* The soluble magnesium oxide produced eventually reacts with hydrogen at the cathode to produce insoluble magnesium hydroxide or reacts with a hydroxide ion to produce magnesium hydroxide and oxygen.
**The solid magnesium is plated onto the cathode but soon reacts with the small amount of sulphuric acid to produce magnesium sulphate and hydrogen.

Reactions

MgSO4(aq) ↔ MgO(aq) + SO32-(aq)

2MgO(aq) + 4OH-(aq) → 2Mg(OH)2(s) + O2(g)  

SO32-(aq) + H2O(l) → H2SO4(aq)

2H2O(l) → H2(g) + 2OH-(aq)

2H2SO4(aq) + 2MgO(aq) → 2MgSO4(aq)+ O2(g)

2Cu2-(s) + O2(g) → 2CuO(s)

Cu2-(s) + 2OH-(aq)  → Cu(OH)2(s)

2CuO(s) + 4OH-(aq)  → 2Cu(OH)2(s) + O2(g)

CuO(s) + SO32-(aq) ↔ CuSO4(aq)

CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)

 
       The resulting aqueous solution will contain magnesium sulphate (MgSO4) and copper sulphate (CuSO4). It will also contain trace amounts of sulfuric acid (H2SO4) and hydroxide ions (OH-). These can be removed by first adding copper oxide powder which will react with the sulfuric acid to produce water and copper sulfate and filtering. The hydroxide can be removed by suspending a bar of clean copper in the solution, waiting until the precipitate stops forming, and then filtering the solution. The magnesium sulfate can never be fully electrolyzed because the copper is less reactive and more easily separated and plated. The copper sulfate can be separated from the magnesium sulfate through a controlled, slow partial recrystallization.  
(c) Copyright Andrew Spangler 2013