Increasing Acidity

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Jacob Afable 3J
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Joined: Fri Sep 25, 2015 3:00 am

Increasing Acidity

Postby Jacob Afable 3J » Sun Nov 29, 2015 8:04 pm

When asked to list HClO3; HCLO; HCLO2; HClO4 from least acidic to most acidic, why does adding more negatively charged Oxygen atoms increase the acidity? I know that a strong acid completely dissociates in water. In these Bronsted acids, what is the conjugate base?

Samantha Geere
Posts: 14
Joined: Fri Sep 25, 2015 3:00 am

Re: Increasing Acidity

Postby Samantha Geere » Sun Nov 29, 2015 8:18 pm

Because the H is always bonded to one of the oxygens in oxyacids, any factor that weakens the O-H bond makes the substance more acidic. As the number of oxygens bonded to the central atom increases, the oxidation number of the central atom increases. This causes a weakening of the O-H bond strength and an increase in the acidity.
Thus, most acidic: HClO4>HClO3>HClO2>HClO

The conjugate base of these acids are:
HClO: ClO-
HClO2:ClO2-
HClO3:ClO3-
HClO4:ClO4-

Meredith Shuffett 2C
Posts: 24
Joined: Fri Sep 25, 2015 3:00 am

Re: Increasing Acidity

Postby Meredith Shuffett 2C » Mon Nov 30, 2015 3:30 pm

^Question about your response, how does increasing the oxidation number weaken the bond?

Samantha Geere
Posts: 14
Joined: Fri Sep 25, 2015 3:00 am

Re: Increasing Acidity

Postby Samantha Geere » Mon Nov 30, 2015 10:19 pm

The tendency of an atom to draw electrons toward itself increases as the oxidation number of the atom increases.
For example, for HClO4, as the oxidation number of the chlorine atom increases, the atom becomes more electronegative. This tends to draw electrons away from the oxygen atoms that surround the chlorine, thereby making the oxygen atoms more electronegative as well. As a result, the O-H bond becomes more polar. The increased dipole moment caused by the electronegative oxygens pulls the electron density away from the hydrogen, which has a low electronegativity. This makes the hydrogen more prone to dissociate. Thus, the compound becomes more acidic.


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