relative strength of weak acids

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Karina Kong 2H
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relative strength of weak acids

Postby Karina Kong 2H » Sat Dec 07, 2019 3:05 pm

How do bond length and resulting anion stability determine the strength of weak acids? And when do you use one over the other to determine it?

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Re: relative strength of weak acids

Postby Chem_Mod » Sat Dec 07, 2019 6:25 pm

Use bond length for acids of the motif H-A, like HCl and HBr. Look at the stability of the conjugate base for oxoacids of the form A-O-H like HClO2.
For bond length: stronger acids lose protons more easily, and this is more easily done if the bond between H and A is weaker. Longer bonds are weaker.
For oxoacids: the conjugate base after proton donation is of the form HClO-, where the O is negatively charged. If the negative charge can be distributed more over other atoms so that the there is less electron density concentrated on the O, the conjugate base will be more stable. Thus stronger electron withdrawing groups attached to the O (like Cl) will delocalize the negative charge more and better stabilize the conjugate base

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