Quick organic chem question - about acid/base strength

[hs2013]

Why is it that the more stable a conjugate base is, the stronger it's acid?

Would this apply not just to conjugate base but also base and conjugate acid?

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[mehc012]

Why is it that the more stable a conjugate base is, the stronger it's acid?

Would this apply not just to conjugate base but also base and conjugate acid?

Something that is a stable conjugate base doesn't 'need' the proton for stability. It is perfectly fine on its own. Its resistance to losing the hydrogen, therefore is low, meaning that the bond is weak and the proton can disassociate easily.

Now, to reverse it...if something is a strong base, that means that it is strongly attracted to the proton and is more stable in protonated form than without. That means that the conjugate acid is more strongly bonded to the proton and will resist losing it, making it a weaker acid.

Note that I reversed it by switching from 'stable' base to 'strong' base...these two terms do not mean the same thing. In fact, they are rather opposite. A stable base does not tend as strongly towards protonation, and can persist in an unprotonated state. A strong base tends to accept protons quickly, and has a higher affinity for protons than neutral water.

 

[CitrusJ]

Yes, the more stable a base the stronger it's conjugate acid is. Make sure you are correctly defining "stronger acid/base" and "more stable conjugage base/acid"

 

[grivacobae]

Here goes what I was just taught - Strong acids relate to -DeltaG (spontaneity), Ka > 1. Entropy is pretty much # of available energy levels; more energy levels, lower in energy, so therefor a conjugate base with more resonance (there are 3 other factors of course) increases the entropy of the compound, which in turn, stabilizes it more. A more stable conjugate base means it was a strong acid (spontaneous) before being deprotinated. Hope this makes sense!

EDIT: Barely makes sense to me when I read my explanation. Will clearly have a rough time writing my PS.

 

[hs2013]

Something that is a stable conjugate base doesn't 'need' the proton for stability. It is perfectly fine on its own. Its resistance to losing the hydrogen, therefore is low, meaning that the bond is weak and the proton can disassociate easily.

Now, to reverse it...if something is a strong base, that means that it is strongly attracted to the proton and is more stable in protonated form than without. That means that the conjugate acid is more strongly bonded to the proton and will resist losing it, making it a weaker acid.

Note that I reversed it by switching from 'stable' base to 'strong' base...these two terms do not mean the same thing. In fact, they are rather opposite. A stable base does not tend as strongly towards protonation, and can persist in an unprotonated state. A strong base tends to accept protons quickly, and has a higher affinity for protons than neutral water.

So a stable conjugate base means the conjugate base is weak because it doesn't need the proton, therefore it's acid is strong because it would give up it's proton to be in the conjugate base state(product favored vs reactant)?

For the reverse example you gave, in a reaction with a strong base and weak conjugate acid, the conjugate acid would be favored because since the base is strong it is very likely to attach to a proton thus making the reactant side favored because compound would be more stable in the conjugate acid state vs in the base?


Man I hate acids/bases right now, but I ended up getting an A in gen chem and understanding them, just happened to forget it all and now need to learn it all over again.

 

[hs2013]

Here goes what I was just taught - Strong acids relate to -DeltaG (spontaneity), Ka > 1. Entropy is pretty much # of available energy levels; more energy levels, lower in energy, so therefor a conjugate base with more resonance (there are 3 other factors of course) increases the entropy of the compound, which in turn, stabilizes it more. A more stable conjugate base means it was a strong acid (spontaneous) before being deprotinated. Hope this makes sense!

EDIT: Barely makes sense to me when I read my explanation. Will clearly have a rough time writing my PS.

Oh God, after you said deltaG I wanted to shoot myself, I was able to understand that stuff well enough to get A's in gen chem exams, but damn I forgot it all and will eventually have to re-learn it all for the admissions test... suicide.jpg

 

[grivacobae]

Oh God, after you said deltaG I wanted to shoot myself, I was able to understand that stuff well enough to get A's in gen chem exams, but damn I forgot it all and will eventually have to re-learn it all for the admissions test... suicide.jpg

you and me both, when she pulled that little "extra knowledge" into the lecture, I got a few flashbacks the rest of the day

 

[Ismet]

SDN is not for homework help. Closing thread.