What is the pH of a solution of 40.0 g acetic acid, HAc, in 2.00 L of
water? Acetic acid has a
Ka of 1.76 x 10-5.
Because acetic acid is a weak acid, we can make the assumption that x is
much smaller than the initial
concentration of HAc.
Problem :
Explain why HClO4 is more acidic than HClO3.
According to the Pauling-Ricci rule, pKa = 8 - 9f + 4n,
f for
HClO4 is 3
whereas HClO3 has f = 2. Conceptually we can understand why
HClO4 has the lower pKa: the central atom Cl
becomes more electronegative when it is adjoined to more electron-withdrawing
oxygen atoms, and therefore the Cl atom withdraws electron density away from the
oxygen holding the acidic proton. This weakens the bond between the oxygen and
the proton.
Problem :
Why do you suppose H2S is a stronger acid than H2O?
The S-H bond in H2S is much weaker than the O-H bond in
H2O
because O is more electronegative than S. The weakly bonded proton is a mark of
a stronger acid.
