Sciencemadness Discussion Board

Combining definition of acids/bases, with oxidizing/reducing agents?

Neal - 17-9-2022 at 05:40

Definitions of acid/bases include proton transfer, and electron transfer.

Definitions of oxidizing/reducing agents also include proton and electron transfer.

Why not just put all the proton transfer as 1, and the electron transfer, as another?

So therefore what is the difference?

1 answer I have is, in Lewis acid/base reactions electrons are transferred, but not necessarily transferred in oxidizing/reducing reactions.

Another is, Lewis acid/base reactions are reversible, whereas in oxidizing/reducing agents reactions, the electrons are irreversibly transferred.

Also, the most contradicting are strong acid and reducing agents, and strong bases and strong oxidizers. For the 1st 1, HI seems to be the only 1, as I- is the reducing agent, and for the 2nd, KO2 will have to do. What other strong acid + strong reducers are out there?

[Edited on 17-9-2022 by Neal]

SplendidAcylation - 19-9-2022 at 02:14

I don't really feel qualified to answer this properly, but I'll give it a go:

As far as I know, the main difference has to do with the change of oxidation state/number.

In acid-base reactions, none of the oxidation states change, for instance:

OH- + HCl --> H2O + Cl-

On the left, the oxidation states, going left to right, are:
O = -2
H = +1
H = +1
Cl = -1

Aaaand on the right-hand side of the equation, the oxidation states are:
O = -2
H = +1
H = +1
Cl = -1

They are the same!
It qualifies as an acid-base reaction because it fits the Bronsted-Lowry theory (base + acid --> conjugate acid + conjugate base, with a proton being transferred)

And it fits the Lewis theory (H+ and OH- react to form the Lewis adduct, water. First the HCl bond has to be polarized by the approaching negative charge, which is what causes the H+ to materialize in the first place)

A more exotic example:

CH3- + HF ---> CH4 + F-

On the left, the oxidation states are:
C = -4
H = +1
H = +1
F = -1

And on the right, they are the same.

However the part which I don't feel qualified to answer correctly is whether or not it is correct to say that some acid-base reactions are also redox reactions, I can think of a few that fit these criteria:

H- + H+ --> H2

A Lewis base (hydride ion) and a proton react forming a Lewis adduct, it looks like an acid-base reaction to me, but it is also redox, as the oxidation states go from -1 and +1 to 0.


H- + HCl --> H2 + Cl-

It seems to be an acid-base reaction, but oxidation states change too.

In the case of HI being a reducing acid, the way I see it is that the two properties are separate, although caused by similar factors.

When HI donates a proton it is behaving as an acid without any redox behaviour, however, reactions like this are redox reactions, but they do not seem to be acid-base reactions:

2HI + O2 --> 2I2 + 2H2O

The only other strong acid/strong reducing agent I can think of is formic acid.

Please, smarter people, correct my probably many errors!

teodor - 19-9-2022 at 03:37

Oxidation state & valency is an older concept failing to adequately describe the bonding in many compounds (like H2 and I2 in your example) so it should be used with an understanding of its limitation. N=O has 2.5 electron pairs participating in the bond but valency is always an integer.
In two complexes [Cr2O2(NH3)10](NO3)4 and [Cr2O2(NH3)10](NO3)5 both Cr atoms have the oxidation state of III which puzzled scientists who were thinking in the terms of oxidation states only.
I would say that changing the orbital configuration deals more with oxidation/reduction and transferring electrons without changing orbitals is more about acid and bases, but I'd like also to hear a more correct answer from somebody who understands the topic.

[Edited on 19-9-2022 by teodor]

DraconicAcid - 19-9-2022 at 08:01

Acid-base chemistry is a useful concept. Redox chemistry is a useful concept. If you try to combine them into one concept, it becomes a lot less useful.

That said, there is a lot of overlap between the two, especially if you use the Lewis definition of acid-base chemistry. A great example (from a textbook written by Hueey, IIRC) is the formation of pyridine oxide. C5H5N: + O --> C5H5N-O
Obviously, the pyridine is acting as a Lewis base, sharing a pair of electrons with the oxygen. And nobody would deny that this is a redox reaction.

Neal - 21-9-2022 at 03:56

I'd like to know if there is a same reactant + reactant -> product, with getting different products on if you treat it as acid/base or redox.

How bout this 1:

HMnO4 + LiAlH4 --> ?

(Acid and oxidizer) + (base and reducer) -> catastrophic reaction.

But even KMnO4 + LiAlH4 is catastrophic.