Synthesis and recrystalisation of pentaammineaquacobalt (III) nitrate

Question

What is the purpose of using hydrogen peroxide, ammonia, ammonium nitrate,

nitric acid and ethyl alcohol in the above reaction?

Answer 1

Uncomplexed cobalt(III) ion is unstable in aqueous solution - it will oxidize water to form oxygen gas.  Instead, an ammine complex of cobalt(II) is prepared from a salt of Co(II) and ammonia, and then oxidized to cobalt(III) by the hydrogen peroxide.  This oxidation takes place in acidic solution, so the nitric acid lowers the pH and provides nitrate ions to balance the charge of the complex ion.  The ammonium nitrate will serve as an additional source of nitrate ions; unless subjected to a basic pH, it will not act as a source of ammonia.  The ethanol is there to precipitate the final product - polar compounds such as this are not as soluble in ethanol as they are in water, so adding the ethanol to the solution (and chilling it, often) helps recover the solid salt.