Failure to oxidise Fe 2+ to Fe 3+

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SUMMARY

The discussion centers on the failure to oxidize Fe2+ to Fe3+ using air in an acidified iron(II) sulfate solution. The user attempted to bubble air through a mixture of 10g of iron(II) sulfate heptahydrate in 150ml of water with 6ml of concentrated H2SO4, expecting a color change to orange, indicative of Fe3+ formation. Despite following established protocols, the solution remained green, suggesting inefficiencies in the oxidation process. The user also considered alternative methods for generating Fe3+ for metal dissolution, specifically questioning the direct dissolution of copper.

PREREQUISITES
  • Understanding of redox reactions and oxidation states
  • Familiarity with the Nernst equation for calculating electrochemical potentials
  • Knowledge of acid-base chemistry, particularly involving sulfuric acid
  • Experience with chemical reagents such as H2O2 and HCl for oxidation processes
NEXT STEPS
  • Investigate the Nernst equation to determine the actual potentials in the reaction
  • Research the use of H2O2 in HCl for effective oxidation of Fe2+
  • Explore alternative methods for dissolving copper using Fe3+ or other oxidizing agents
  • Examine the effects of concentration and temperature on the oxidation rate of Fe2+ in acidic solutions
USEFUL FOR

Chemists, chemical engineers, and hobbyists involved in metal etching or oxidation processes will benefit from this discussion, particularly those looking to optimize the oxidation of iron in various chemical applications.

mooliak
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Hi all,

I have a problem which is quite basic, and I must be missing something.
Fe 3+ + e > Fe 2+ +0.77v
O2 + 4H+ + 4e > 2H2O +1.23v

Re arranged, this tells us that if we bubble air through iron 2 sulphate solution, acidified with H2SO4, the oxygen should oxidise the Fe 2+ to Fe 3+ using the protons from the sulphuric acid. Many texts also say this. However, when I put approx. 10g of green iron 2 sulphate heptahydrate into about 150ml water and add about 6 ml of c.H2SO4, and bubble air through it from a fish tank aerator, it stays green, and does not go orange as one would expect. How is this?

My project is quite simple. I want to generate Fe 3+ to dissolve metals like copper. It is a good agent to do this, but on reflection, could I not dissolve the copper directly, as the oxidation potential is easily high enough. Or would there be a rate problem?

Any suggestions would be greatly appreciated.
 
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I would plug the concentrations into Nernst equation to see where you are - potentials you listed are standard ones, formal will be different.

As far as I know best way of oxidizing Fe2+ for etching is done with H2O2 in HCl.
 

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