Redox half reactions

I would like to ask if MnO2 -> Mn2+ is oxidation or reduction. Im confused if we look at Oxygen it is reduction but if we look at electrons it will be added on the product side so it will be oxidation.
Please advice..
Thanks

Reply 1

jjeeeeeea

Both looking at oxygen and at electrons suggest reduction.
2 electrons are gained by MnO2, the full reaction being:
MnO2 + 4H+ + 2e- --> Mn2+ + 2H2O

MnO2 contains ions Mn4+ and O2-, so Mn4+ must gain electrons to form Mn2+ = reduction
so you are basically looking at Mn4+ +2e- -> Mn2+

(edited 11 months ago)

Reply 2

charco

Study Forum Helper

Original post by Mereani Bati

You must also look at where the oxygen goes to consider whether or not it is oxidised or reduced.

In this case it ends up in water, with an oxidation state of -2, the same as in MnO₂, so it is neither oxidised nor reduced.

The only element changing its oxidation state is manganese from +4 to +2