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.
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.
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.