[gavindor]

Looking at this reaction

H2O  + Na2O  --> 2NaOH

Is that a Bronsted acid and Bronsted base..  (a bronsted acid since water is an amphoteric molecule and is an acid here).   And Na2O is a base.

But two interesting things I notice about this.

It seems to me that

- It's not a neutralisation reaction.. Because NaOH has a pH not equal to 7. NaOH's pH is not neutral.

- There's no conjugate acid and conjugate base.

The product is one product 2NaOH,    which could be seen as  NaOH + NaOH   

But to be a conjugate acid and conjugate base, there'd have to be two products, the products would be different, one positive one negative , and those products would have to be  Na2OH+  + OH-

So am I correct that it's a bronsted acid base reaction, but not a neutralisation reaction, and with no conjugate acids/base pairs?
 

[Hunter2]

You have to look to the oxide anion O2-. This is an Proton acceptor, means a base.
H+ + O 2- => OH-
Water is a Proton donator it is the acid.
H2O => H+ + OH-

In sum

O2- + H2O =>  OH- + OH-

The hydoxid two times on product side works  also one as the Proton acceptor what will form water again the other one is the Proton donator to form the oxide ion.

O2- ( base I) + H2O (acid I) =>  OH- ( base II) + OH- ( acid II)

The same we have with equilibrium  of water

2 H2O => H3O+ + OH-

One water is acid, the other one base.

[gavindor]

I know H+ goes from the H2O to the  Na2O     

H2O  + Na2O  --> 2NaOH

so OK it's a bronsted lowry acid base reaction.

I suppose  H2O  + Na2O  --> 2NaOH

is the same as

H2O  + Na2O  --> NaOH + NaOH

So one NaOH is the conjugate acid, and one NaOH is the conjugate base?

[Hunter2]

Correct

[gavindor]

thanks, and would you call it a neutralisation reaction (even) if the salt is not neutral?

[gavindor]

So one NaOH is the conjugate acid, and one NaOH is the conjugate base?

Correct

But doesn't the conjugate acid have to have a positive charge, and the conjugate base a negative charge?

NaOH whether you look at it as Na+(OH)-  or whether you look at it as   H+ NaO  it's neutral. 'cos H is +1,  Na is +1,  O is -2.

So it seems to me that NaOH can't be a conjugate acid or a conjugate base.

Even though it works from the donation of H+ and acceptance of H+ perspective

H2O + Na2O   

becomes  OH- + Na2OH   

=  OH-  + Na +  + NaOH   =  NaOH + NaOH = 2NaOH


So the transfer of H and acceptance of H works.

But I can't see how NaOH is a conjugate acid and/or conjugate base.

I can see how   OH-  and Na2OH+  are   conjugate base and conjugate acid respectively.

And then simplify to 2NaOH

But it seems to me.. The Conjugate base is OH-  ,  and the Conjugate acid is Na2OH+

[Borek]

But doesn't the conjugate acid have to have a positive charge, and the conjugate base a negative charge?

No. They have to differ by one charge as they interconvert by accepting/donating proton, but the definition doesn't say anything about the initial charge value.

I would not call NaOH neither Bronsted acid nor base. Na⁺ is just a spectator, it is OH^- that is reacting.

In this case I would say O^2- is a Bronsted base (accepts a proton), H₂O is a Bronsted acid (donates a proton):

O^2- + H₂O OH^- + OH^-

O^2-/OH^- is one conjugate acid/base pair, H₂O/OH^- is another. Yes, OH^- can be thought as both Bronsted acid and Bronsted base in two different reactions. A bit stretching, but technically correct.

Na2OH+

I doubt something like that exists, making things up is not a way forward. Na₂O is highly ionic.

[gavindor]

But doesn't the conjugate acid have to have a positive charge, and the conjugate base a negative charge?

No. They have to differ by one charge as they interconvert by accepting/donating proton...Na⁺ is just a spectator...

I guess you don't mean to say that the conjugate acid and conjugate base should differ by one..

You mean to say that the (non-conjugate)acid and conjugate base, should differ by 1.  And that the (non-conjugate) base, and conjugate acid, should differ by 1.

It seems to me that the conjugate acid and conjugate base could have the same charge and do in this example. 


e,g. So in Na2O + H2O --> 2NaOH

Given that  Na is just a spectator ion..  (or taking Na as a spectator ion)..

Our "non-conjugate acid" is H2O

Our "non-conjugate base" is O

Our conjugate base is OH-   (H2O minus H)

Our conjugate acid is OH-  (O plus H)


Our "non-conjugate base" and conjugate acid differ by 1

Our "non-conjugate acid" and conjugate base, differ by 1

And that makes sense because it's a transfer of H+   to make a difference of a charge of 1

I notice that here we have conjugate base of OH- and conjugate acid of OH-

That sounds similar to saying NaOH is the conjugate base and NaOH is the conjugate acid.. just excluding the spectator ion. But perhaps more technically correct to exclude the spectator ion, as you do.

Our conjugate acid and conjugate base have the same charge. Not differing by one.

Often they can differ by two, which they would if the conjugate acid is + and the conjugate base is -   like HCl + NH3 <-->  NH4+ + Cl-

But you make an interesting point that the conjugate acid and base don't have to be + and - respectively. And in the Na2O + H2O example they're the same.  OH-  so same charge.  I can see that if the charges of the non-conjugate acid and non-conjugate base are neutral, then you get + and - with the conjugate acid and conjugate base. And that supports what you show about not counting the Na+.

[Borek]

I guess you don't mean to say that the conjugate acid and conjugate base should differ by one.

That's exactly what I am saying.

Looks to me like you are confused about what conjugate acid and base are - these are things that react directly by transferring a proton between them. They always come as conjugate pairs. We do have two pairs of conjugate acid/base here, OH^-/O^2- and H₂O/OH^-, in each pair their charges differ by one. None of these substances is "non-conjugate".

It is perfectly possible for something to be both conjugate acid and conjugate base in different pairs. In such cases there is no way to tell whether something is a conjugate base or conjugate acid without stating the context (typically just mentioning the other conjugate of the pair is enough). That's what OH^- does here.

[gavindor]

I guess you don't mean to say that the conjugate acid and conjugate base should differ by one.

That's exactly what I am saying.

Looks to me like you are confused about what conjugate acid and base are - these are things that react directly by transferring a proton between them. They always come as conjugate pairs. We do have two pairs of conjugate acid/base here, OH^-/O^2- and H₂O/OH^-, in each pair their charges differ by one. None of these substances is "non-conjugate".

It is perfectly possible for something to be both conjugate acid and conjugate base in different pairs. In such cases there is no way to tell whether something is a conjugate base or conjugate acid without stating the context (typically just mentioning the other conjugate of the pair is enough). That's what OH^- does here.

Here is how i've seen the terms used.




So certainly a conjugate pair would differ by one

But a conjugate pair involves a (non-conjugate) acid and conjugate base,  or a  (non-conjugate) base and conjugate acid

A conjugate acid and conjugate base, wouldn't be a conjugate pair.

A conjugate pair is one from the left and one from the right. (an acid from the left and corresponding base from the right). Or a base from the left and corresponding acid from the right).

If you say "conjugate acid and conjugate base should differ by one."

Then I think you are using the terms differently than the examples of usages of terms in that image.

'cos a pair that should always differ by one, wouldn't be composed of two on the right.

You seem to be considering O2-  , which is on the left, to be a conjugate base, and then the OH- on the right, a conjugate acid.  So then you can say that the conjugate acid and conjugate base differ by one. But it doesn't seem to be standard usage looking at that image, to refer to a formula unit or ion or atom on the left to be a conjugate acid or conjugate base.  Based on the image i've shown, those terms seem to be reserved for that which is on the right of the equation.

[Borek]

Just because sometimes one "conjugate" is omitted doesn't mean acid and base of a pair are not both conjugate. There is a full symmetry. What you suggest is that sometimes one of the pair (selected at random) is not "conjugate" for no apparent reason.

[gavindor]

Just because sometimes one "conjugate" is omitted doesn't mean acid and base of a pair are not both conjugate. There is a full symmetry. What you suggest is that sometimes one of the pair (selected at random) is not "conjugate" for no apparent reason.

It's not for no reason, I think they're saying the one on the right is derived.

This one for example doesn't just not use the word conjugate for those on the left, but it marks the ones on the left as the parent.

https://courses.lumenlearning.com/suny-mcc-organicchemistry/chapter/bronsted-lowry-acids-and-bases/



Looking on google images, most examples don't have the word conjugate on the left. I think because the word conjugate can suggest it's a derivation..

But you could look at the ones on the left as conjugates.. in the sense of being alike.

And I did find two images  on google images that use your approach in labelling.. plus an entry on marriam webster. https://www.merriam-webster.com/dictionary/conjugate  "The acid NH4+ and the base NH3 are conjugate to each other."

https://www.chemistrystudent.com/acidsandbases.html



https://www.researchgate.net/figure/Examples-of-acid-base-conjugate-pairs_fig1_352039113




From what I understand there might be some technicality with arrows in a reaction, whether the arrows are making a statement about the equilibrium or the reversibility or even perhaps both.. If they're making a statement about reversibility then I suppose you could say that both the LHS and RHS are derived. 

[Borek]

It's not for no reason, I think they're saying the one on the right is derived.

And how do you select which one is "original" and which one is "derived"?

[gavindor]

And how do you select which one is "original" and which one is "derived"?

well it's a bit flawed 'cos the reaction is reversible so while they want to say the products are derived, one could also say the reactants are derived.

[gavindor]

So for Na2O + H2O --> 2NaOH, we have the conjugate acid-base pairs.   

OH^-/O^2- and H₂O/OH^-

So we have the  conjugate base on the left of the equation  O2-,  gaining an H+ and becoming the conjugate acid OH-

And we have the conjugate acid on the left of the equation  H2O, losing an H+, and becoming the conjugate base OH-


Does that apply to all metal oxides, that the metal oxide is not a bronsted lowry base, only the oxide anion is. And the metal is a spectator ion?

So likewise for CaO + 2HCl --> CaCl₂ + H₂O?

Would you say the conjugate pairs are  O²⁻ / H2O.   And  HCl/Cl

One possible issue I have with those pairs, is that O²⁻ receives -two- Hydrogen cations to become H2O. But I suppose that's ok?