# conjugate pairs, Brønsted-Lowry theory

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Brønsted-Lowry denotes that Acids are proton doners and bases are Proton acceptors....fine:

So why is it that a weak acid like HCLO4 can be made by its conjugate pairs H+ and CLO4-

but a strong acid like H2SO4 or HNO3 will not

i.e.

a strong acid can be split in the following way

HCL >>> (H+)(Cl-)

but

(H+)(Cl-) will not join to give HCL

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Brønsted-Lowry denotes that Acids are proton doners and bases are Proton acceptors....fine:

So why is it that a weak acid like HCLO4 will split in to its conjugate pairs H+ and CLO4-

but a strong acid like H2SO4 or HNO3 will not

i.e.

a strong acid can be made in the following way

(Cl-)+(H+) >>> HCL

but

HCL will not split to give (CL-) and (H+)

$HCl$ will split to give $H^+ + Cl^-$ if placed into water. The fact that it completely ionizes means its conjugate base $Cl^-$ is a weaker base than the $H_2O$. This is because the $H_2O$ is able to attract the $H^+$ ions more than the $Cl^-$ ions can. In other words, the stronger the acid, the weaker its conjugate base, and the weaker the acid, the stronger it conjugate base. Since the $HClO_4$ you spoke of is a stong acid, it will have a weak conjugate base. If it were a weak acid, it would have a strong conjugate base. This means it will not completely ionize, and thus you'll have a reversible reaction on your hands. Conversely, the HCl placed into water will completely ionize, and the recation will not be a reversible one. I hope that helps.

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thanks for the answer hotcommodity im sorry the question i posted was screwed up, i have edited it and the correct one is now at the top

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thanks for the answer hotcommodity im sorry the question i posted was screwed up, i have edited it and the correct one is now at the top

Don't sweat it. Understand that $HCl$ is a strong acid, and strong acids completely ionize in water. Both $HCl$ and $H_2O$ are polar, which is to say they have both strong negative and positive portions associated with each molecule. When the partial positive portion of the $H_2O$ molecules cling to the partial negative portions of the $HCl$ compound, and the partial negative portions of the $H_2O$ molecules cling to the partial positive portions of the $HCl$ compound, the$HCl$ compound is pulled apart. We know that since $HCl$ is a strong acid, it will have a weak conjugate base $Cl^-$. That weak conjugate base is considered weak because it can't hang on to the $H^+$ ion. If you still have questions feel free to come back.

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thats great, thanks Hotcommodity, you really helped clear that up! it was really bugging me

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Er?

"So why is it that a weak acid like HCLO4 can be made by its conjugate pairs H+ and CLO4- "

??

HClO4 is an exceptionally strong acid.

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Er?

"So why is it that a weak acid like HCLO4 can be made by its conjugate pairs H+ and CLO4- "

??

HClO4 is an exceptionally strong acid.

The site construction screwed up the LaTex, grrrr >:|

HClO4 is not a weak acid. When placed in water, it completely ionizes, and never returns to its old form, just as all other strong acids do.

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