Pyrophosphoric acid contains pyrophosphate ions, P2O74−\text{P}_2\text{O}_7^{4-}P2O74−.
Pyrophosphoric acid is completely neutralised by iron(III) hydroxide.
What is the formula of the salt that is produced?
Fe3(P2O7)4\text{Fe}_3(\text{P}_2\text{O}_7)_4Fe3(P2O7)4
Fe(P2O7)3\text{Fe}(\text{P}_2\text{O}_7)_3Fe(P2O7)3
Fe4(P2O7)3\text{Fe}_4(\text{P}_2\text{O}_7)_3Fe4(P2O7)3
Fe3P2O7\text{Fe}_3\text{P}_2\text{O}_7Fe3P2O7