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.