Oxidation and reduction in terms of loss/gain of oxygen and hydrogen

We're all familiar with the OILRIG mnemoic which stands for "Oxidation is loss, Reduction is gain" of electrons. I understand these simple definitions as the gain of electrons decreases the charge and thus the oxidation number of atoms. And the reverse is true, also.

However I'm a little unsure why gain of oxygen and loss of hydrogen is oxidation and loss of oxygen and gain of hydrogen, reduction.

(I see this mainly in Biology which I'm currently working on but this is really a chemistry question)

If I had to imagine why, is it because the species to which Oxygen is added donates (an) electron(s) to the oxygen in order to allow it to complete its valence shell? And so Oxygen functions as as a oxidising agent as it accepts those electrons?

And similarly, for the other cases. I don't wish to repeat myself.

Thanks :smile:

(edited 8 years ago)

Reply 1

Plantagenet Crown

20

Original post by Kvothe the arcane

We're all familiar with the OILRIG mnemoic which stands for "Oxidation is loss, Reduction is gain" of electrons. I understand these simple definitions as the gain of electrons decreases the charge and thus the oxidation number of atoms. And the reverse is true, also.

However I'm a little unsure why gain of oxygen and loss of hydrogen is oxidation and loss of oxygen and gain of hydrogen, reduction.

(I see this mainly in Biology which I'm currently working on but this is really a chemistry question)

If I had to imagine why, is it because the species to which Oxygen is added donates (an) electron(s) to the oxygen in order to allow it to complete its valence shell? And so Oxygen functions as as a oxidising agent as it accepts those electrons?

And similarly, for the other cases. I don't wish to repeat myself.

Thanks :smile:

In terms of adding oxygen and hydrogen, I remember reading that they used to be the old definition of oxidation and reduction, possibly before the intricacies of the electron transfers were known. Most chemists find the electron definitions more useful.

(edited 8 years ago)

Reply 2

xylas

21

Original post by Kvothe the arcane

We're all familiar with the OILRIG mnemoic which stands for "Oxidation is loss, Reduction is gain" of electrons. I understand these simple definitions as the gain of electrons decreases the charge and thus the oxidation number of atoms. And the reverse is true, also.

However I'm a little unsure why gain of oxygen and loss of hydrogen is oxidation and loss of oxygen and gain of hydrogen, reduction.

(I see this mainly in Biology which I'm currently working on but this is really a chemistry question)

If I had to imagine why, is it because the species to which Oxygen is added donates (an) electron(s) to the oxygen in order to allow it to complete its valence shell? And so Oxygen functions as as a reducing agent as it accepts those electrons?

And similarly, for the other cases. I don't wish to repeat myself.

Thanks :smile:

Good question, it's not made clear in the national curriculum but fortunately it is very easy!

Oxygen is an oxidising agent. In fact, past chemists used to believe oxidation had to involve oxygen (Re: fire triangle) but there are much more powerful oxidisers out there.

Hydrogen is a reducing agent. That's why compounds with lots of hydrogen atoms in them, e.g. sugars, are also reducing agents (you may have heard the term 'reducing sugar' for the same reason).

In biology, this level of understanding is enough but in chemistry it is better to think in terms of electrons only. Your imagined model is correct in that oxygen likes to accept electrons to become a 2- oxide anion. However, in doing so it has caused the species to lose 2 electrons and a loss of electrons is called oxidation. Remember that oxygen oxidises and you won't go wrong!

(edited 8 years ago)

Reply 3

Kvothe the Arcane

OP

20

Original post by Plantagenet Crown

In terms of adding oxygen and hydrogen, I remember reading that they used to be the old definition of oxidation and reduction, possibly before the intricacies of the electron transfers were known. Most chemists find the electron definitions more useful.

Your memory seems to be correct based upon what the user below you has said. And indeed, we only considered electron transfer when discussing redox reactions in Chemistry :yep:

.

Original post by xylas

Reply

Thanks for your reply :smile:

It was very helpful.

I think I understand now :biggrin:

.

Reply 4

xylas

21

Original post by Kvothe the arcane

Thanks for your reply :smile:

It was very helpful.

I think I understand now :biggrin:

.

Excellent! Glad I could help :h:

Reply 5

User947387

17

Original post by Kvothe the arcane

We're all familiar with the OILRIG mnemoic which stands for "Oxidation is loss, Reduction is gain" of electrons. I understand these simple definitions as the gain of electrons decreases the charge and thus the oxidation number of atoms. And the reverse is true, also.

However I'm a little unsure why gain of oxygen and loss of hydrogen is oxidation and loss of oxygen and gain of hydrogen, reduction.

(I see this mainly in Biology which I'm currently working on but this is really a chemistry question)

If I had to imagine why, is it because the species to which Oxygen is added donates (an) electron(s) to the oxygen in order to allow it to complete its valence shell? And so Oxygen functions as as a oxidising agent as it accepts those electrons?

And similarly, for the other cases. I don't wish to repeat myself.

Thanks :smile:

Oxidation loss of an electron. Given that electrons are ALWAYS negative.... this means there is an increase/gain in oxidation number.

Its like we have lost a debt :smile:

Reply 6

username1445490

9

It has to do with change in oxidation number. If the oxidation number increases (becomes more positive) then oxidation has occurred but if it decreases (becomes more negative) then reduction has occurred. Compare carbon's oxidation number in methanol and methanoic acid: in methanol the C has an ox no. of -2 but in methanoic acid it is +2 so it has been oxidised by adding oxygen. If you reduced the methanoic acid to methanol by adding hydrogen the ox no changes from +2 to -2 which is reduction.

Reply 7

Asad_2015

12

Original post by Kvothe the arcane

We're all familiar with the OILRIG mnemoic which stands for "Oxidation is loss, Reduction is gain" of electrons. I understand these simple definitions as the gain of electrons decreases the charge and thus the oxidation number of atoms. And the reverse is true, also.

However I'm a little unsure why gain of oxygen and loss of hydrogen is oxidation and loss of oxygen and gain of hydrogen, reduction.

(I see this mainly in Biology which I'm currently working on but this is really a chemistry question)

If I had to imagine why, is it because the species to which Oxygen is added donates (an) electron(s) to the oxygen in order to allow it to complete its valence shell? And so Oxygen functions as as a oxidising agent as it accepts those electrons?

And similarly, for the other cases. I don't wish to repeat myself.

Thanks :smile:

Originally anything that had the addition of oxygen was called an oxidation reaction, and since hydrogen was added to remove oxygen, addition of hydrogen was called reduction. But since then the new definition is the loss and gain of electrons one.

Oxidation and reduction in terms of loss/gain of oxygen and hydrogen

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