Sciencemadness Discussion Board

bronsted-lowry vses lewis quick Q

SunriseSunset - 20-10-2015 at 18:01

My question is: Can Lewis acid/base and bronsted-lowry acid/base definitions and mechanisms be used in place of one another interchangeably for any acid base reaction? depending on which you prefer, or does bronsted-lowry only work on some, and lewis work on the other ones?

I think I'm answering my own question. I'm working on learning mechanisms and I feel like I understand the bronsted-lowry so far. And I like it

blogfast25 - 20-10-2015 at 18:15

Quote: Originally posted by SunriseSunset  
My question is: Can Lewis acid/base and bronsted-lowry acid/base definitions and mechanisms be used in place of one another interchangeably for any acid base reaction? depending on which you prefer, or does bronsted-lowry only work on some, and lewis work on the other ones?

I think I'm answering my own question. I'm working on learning mechanisms and I feel like I understand the bronsted-lowry so far. And I like it


They are definitely related but not the same.

BL is limited to solution chemistry and is quite exact. Solvents need themselves to be acids or bases in BL theory.

Lewis is not restricted to solvated chemistry and is not as exact (no definitive quantitative models) as BL.

There is overlap as well as clear distinctions between BL and L and you really need to study both theories to appreciate that. Do it because it's very rewarding. :):)

Related: quantum chemistry:

http://www.sciencemadness.org/talk/viewthread.php?tid=62973&...


[Edited on 21-10-2015 by blogfast25]

SunriseSunset - 20-10-2015 at 19:42

I'm starting to understand it. Just takes step by step practice until the painting starts to fill in more. Thank you again!

deltaH - 20-10-2015 at 20:15

There's an interesting overlap between a Bronstead acid and a Lewis acid, that is when you mix the two to make a stronger acid or superacid. For example, antimony pentafluoride, SbF5, is a strong lewis acid. Hydrogen fluoride is a weak Bronstead acid making the fluoride ion a strong lewis base. When you mix the two, the strong lewis acid will bond to the strong lewis base, strongly and you end up with hexafluoroantimonic acid, HSbF6, the strongest Bronstead acid in the world because the proton is very nearly fully ionised in any solvent because the equilibrium towards forming the SbF6- anion is very much favoured.

This can also happen within the same acid, for example, dilute solutions of hydrogen fluoride in water are weak lewis acids but the fluoride ion is a strong lewis base, so in concentrated solutions you will form high concentrations of bifluoride ions, HF2- and much higher concentrations of H3O+ and so the weak acid starts to behave like a strong acid by itself.

SunriseSunset - 21-10-2015 at 19:50

Is the reaction H2O2 with Formic acid to yield Performic acid a acid base reaction?

I'm understanding so far that due to pKa values, H2O2(BL-Acid) + H2O(BL-Base) -> H-O-O(-)(conjugate base) + H3O(+)(conjugate acid), they should dissociate and the same for Formic acid in water,

Formic acid + water -> Formate(-) and Hydronium(+).

So I get the mechanism on how they dissociate in water this far. But does this reaction go to completion by just plain acid and base chemistry alone, What do I not yet have understood? or is the final part that brings together formate(-) and H-O-O-(-) a redox reaction?

I'm going to study redox reactions tomorrow