Depronatation

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Natalie Yakobian
Posts: 45
Joined: Fri Sep 25, 2015 3:00 am

Depronatation

Postby Natalie Yakobian » Thu Dec 03, 2015 4:20 pm

Why is the percentage deprotonation of benzoic acid in a benzoic acid solution decreased when hydrochloric acid?

Wouldn't the H30+ interact with the conjugate base of benzoic acid?

Thank you!

Umair Khan 2G
Posts: 32
Joined: Fri Sep 25, 2015 3:00 am

Re: Depronatation

Postby Umair Khan 2G » Thu Dec 03, 2015 4:33 pm

The Equation for Benzoic Acid is :

When Hydrochloric Acid is added, which I'm assuming is the question, there is a 100% disassociation, meaning that HCl splits into a proton and Cl-.
The proton normally would increase the concentration of H3O, but since Benzoic acid acts as a buffer, its conjugate base picks up the proton from HCl and forms benzoic acid again, making sure the pH doesn't change:

So overall, the concentration of Benzoic acid increase, its conjugate base decreases, and the pH stays constant. Because more benzoic acid is produced with the buffer solution, the percentage deprotonation decreases.


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