Ch 16 question about acidity and structure - Part 2

[Zellmer, Robert]

I got the following question from a couple of students and I've had it before.

"In a series of acids that have the same central atom, acid strength increases with the
number of hydrogen atoms bonded to the central atom."

I don't understand why this statement is false because H2SO4 is a stronger acid than
HSO4-.  And lots of other acids also become weaker acids after they lose one
hydrogen.

This part is true, the Ka for the 1st proton coming off is bigger than the Ka for the 2nd
proton coming off, and so forth.  Look at the statement closely.  I'll bold the impt.
part.

"In a series of acids that have the same central atom, acid strength increases
with the number of hydrogen atoms bonded to the central atom."

You're confusing what we covered concerning acid strength and structure and this.
For the same central atom the acid strength increases with increasing numbers of
 atoms, e.g. H2SO4 is stronger than H2SO3.

The statement is "number of hydrogen atoms bonded to the central atom".  For
oxyacids the acidic H atoms are NOT bonded to the central atom in general.  They
are normally bonded to the O atoms.  The main exception to this is H3PO3 in
which one of the H atoms is on the P.

Wed and Thur, I sent out a couple of e-mails addressing acid structure and strength
and which H atoms are acidic in various types of acids.

Dr. Zellmer
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