What is #Fe_3O_4#, and how do we represent its formation from iron, and water?

1 Answer
Aug 28, 2017

Answer:

This is a mixed valence oxide of #FeO# and #Fe_2O_3#........

Explanation:

In the original redox reaction, elemental iron is OXIDIZED to #FeO + Fe_2O_3#, i.e. #FeO*Fe_2O_3-=Fe_3O_4#.

And so we write 2 separate oxidation rxns....

#Fe +H_2O rarr FeO+2e^(-) +2H^+#, and....

#2Fe +3H_2O rarr Fe_2O_3+6H^(+) + 6e^(-)#

We adds these together and get.....

#3Fe +4H_2O rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4) +8H^(+) + 8e^(-)# #(i)#

And for every oxidation, electron loss, there is a corresponding reduction, electron gain, and the most likely oxidant is dioxygen gas.....

#1/2O_2 + 2H^+ + 2e^(-)rarrH_2O# #(ii)#

And so we take #4xx(ii)+(i)# to eliminate the electrons from our final redox equation.......

#3Fe +2O_2 + cancel(4H_2O +8H^(+) + 8e^(-)) rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4) +cancel(8H^(+) + 8e^(-)+4H_2O)#

To give finally.......

#3Fe +2O_2 rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4) #

#Fe_3O_4# is a mixed valence iron oxide.....#Fe_2O_3*FeO#