Chemistry of pyrophosphate paths. Copper pyrophosphate, Cu2P2O7•3H2O, dissolved in potassium pyrophosphate, K4P2O7 solution, forms the stable complex ion Cu(P2O7)26- from which copper plates. Potassium is used instead of sodium because it is more soluble and has a higher electrical conductivity. Any pyrophosphate in excess of this ratio is called “free” pyrophosphate. Free pyrophosphate is essential for the operation of the bath, providing conductivity and anode corrosion.