The Prussian blue is a component of black and bluish inks for printing. The precipitate formed upon — Physical Chemistry Chemistry Question
The Prussian blue
The Prussian blue is a component of black and bluish inks for printing. The precipitate formed upon the dropwise addition of potassium ferrocyanide to the ferric chloride solution contains 34.9 % (mass) of iron.
Give a formulae of the precipitate and write the chemical equation. (Use 55.8 for atomic mass of iron).
Model Answer
The precipitate is Fe7(CN)18 · 14.5 H2O.
4 Fe3+ + 3 [Fe(CN)6] 4− → FeIII[FeIIIFeII(CN)6]3
Using the crystal field theory show the d-orbital splitting pattern for all Fe atoms in the Prussian blue.
What causes the intense color of the pigment?
Model Answer
Most inorganic pigments contain ions that produce colors by selective absorption of specific wavelengths of electromagnetic radiation due to the electron transitions.
The intense blue color of Prussian blue is associated with the energy of the transfer of electrons from Fe(II) to Fe(III) via the bridging cyanide group.
What product initially forms from potassium ferrocyanide and ferric chloride solution in the inverse-mixing-order route? Give the equation.
Model Answer
In the inverse-mixing-order route a "soluble" colloidal Prussian blue forms:
K+ + Fe3+ + [Fe(CN)6] 4− → K[FeIIIFeII(CN)6]
Soluble Prussian blue contains interstitial K+ ions instead of interstitial water, that is present in the insoluble form.