3. Theory
The complex iron hexacyano ferrate is known as
prussian blue
It is obtained by oxidation of iron, Fe to Fe3+, followed
by reaction with potassium ferrocyanide.
Fe + H2SO4 → FeSO4 + H2
2FeSO4 + H2SO4 +[0]→ Fe2 (SO4)3 +H20
Fe2 (SO4)3 + 2K2[Fe(CN)6]3 → Fe4[Fe(CN)6]3 + 5K2SO4
Fe → Fe4[Fe(CN)6)3
MW = 55.85 g MW = 859.25 g
6. Procedure
Take 0.5 g of iron filings in a beaker.
Add 10 ml of dil. sulfuric acid.
Heat it on a wire guaze.
The reaction becomes vigorous
Remove the burner and cool the solution.
When the reaction subsides, decant the supernatant liquid in
another beaker.
Add 10 ml of dil. sulfuric acid
Repeat the procedure till whole iron filings are dissolved.
Combine the solution of ferrous sulfate and heat it.
Add 0.5 ml conc. HNO3 and boil to oxidize iron to ferric state.
The solution becomes yellow. Continue boiling for 5 minutes to
expel fumes of NO2 gas and nitric acid.
Add the saturated solution of 4.5 g of potassium ferrocyanide.
Heat the solution until it acquires green color.
Keep the green colored product in air for 2 hours
It changes to blue.
Filter the product, wash with a little alcohol, dry and weigh it.
8. Note
• Addition of 1-2 ml of K2Cr203 will increase the
oxidation öf green product.
• Prussian blue may also be obtained by the
reaction of potassium ferrocyanide with ferric
chloride.
• Prussian blue may be manufactured by
roasting mixture of iron filings, potassium
carbonate and organic proteinous matter. But
no satisfactory yields