Redox Reactions (1 Viewer)

[ghuy]

Hey everyone,

These questions are driving me insane, (especially thanks to my teacher ) anyways, how do I go about doing these types of questions:

"In each of the following equations, state which (if any) element has been oxidised and which has been reduced:"

4Fe +3O2 -> 2Fe2O3


I understand that Fe is oxidised 4Fe->4Fe^(3+)+12e-
but I don't get why the reduction part:
3O2 + 12e^- ->6O^2-

How do I approach these questions?

Thanks!

 

[QZP]

Hey everyone,

These questions are driving me insane, (especially thanks to my teacher ) anyways, how do I go about doing these types of questions:

"In each of the following equations, state which (if any) element has been oxidised and which has been reduced:"

4Fe +3O2 -> 2Fe2O3


I understand that Fe is oxidised 4Fe->4Fe^(3+)+12e-
but I don't get why the reduction part:
3O2 + 12e^- ->6O^2-

How do I approach these questions?

Thanks!

Oxidation is the loss of electrons; reduction is the gain of electrons.
In your half equations you have clearly expressed iron losing electrons and oxygen gaining the electrons. Thus it follows that iron is oxidised and oxygen is reduced.

 

[ghuy]

Oxidation is the loss of electrons; reduction is the gain of electrons.
In your half equations you have clearly expressed iron losing electrons and oxygen gaining the electrons. Thus it follows that iron is oxidised and oxygen is reduced.

Sorry, I don't think I was very clear, but I meant why is it 12e- forming 6O2- ??

 

[study1234]

Sorry, I don't think I was very clear, but I meant why is it 12e- forming 6O2- ??

Like QZP said above, oxidation is the loss of electrons and reduction is the gain of electrons. A good way of remembering this is OIL RIG (Oxidation Is Loss; Reduction Is Gain).

However, another way of looking it is comparing oxidation state. The oxidation state is the charge of a species (ion, atom, molecule, etc). For example 6O2- has an oxidation state of 2-, while 4Fe3+ has an oxidation state of 3+. Using this, oxidation is the INCREASE in oxidation state (i.e. 4Fe->4Fe^3+ + 12e-), while reduction is the DECREASE (or REDUCTION) in oxidation state (i.e. 3O2 + 12e- ->6O^2-).

So in this case,

Oxidation: 4Fe->4Fe^3+ + 12e-
Reduction: 3O2 + 12e- ->6O^2-

To answer your question, the 12e- are given to O2 so it 'gains' electrons (i.e. reduction).

 

[anomalousdecay]

Sorry, I don't think I was very clear, but I meant why is it 12e- forming 6O2- ??

The oxygen atoms gain extra electrons to form the ions O2-.