• Acids with one or more ionizable proton are polyprotic acids. In this acid, one
proton at a time dissociates from the acid molecule, and each dissocation steps has
a different Ka.
• For every polyprotic acid, the first proton comes off to a much greater extent than
the second and where applicable the second does to a much greater extend than
• It is more difficult for an H+ ion to leave a singley charged anion such as H2PO4
– than to leave a neutral molecule such as H3PO4 and more difficult still for it
leave a double charged anion HPO4 2.
• A base is any species that accepts a proton; to do so the base must have a lone
• The strength of an acid depends on its ability to donate a proton, which depends in
turn on the strength of the bond to the acidic proton.
• Trends in Acid Strength of nonmetal hydrides:
o 1. Across a period nonmetal hydride acid strength increases. Across a
period the electronegativity of the nonmetal E determines the trend. As E
becomes more electronegative the electron density around H is withdrawn.
o 2. Down a group nonmetal hydride acid strength increases.
• Trends in Acid Strength of Oxoacids
o All oxoacids have a the acidic H atom bonded to an O atom, so bond
strength is not a factor in their acidity as it is with the nonmetal hydrides.
o 1. For oxoacids with the same number of oxygen’s around E, acid strength
increases with the electronegativity of E.
o 2. For oxoacids with different numbers of oxygen’s around a given E, acid
strength increases with number of O atoms. The electronegative O atoms
pull electron density away from E, which makes the OH bond more polar.
• A salt consiting of the anion of a strong acid and the cation of a strong base yields
a neutral solution because the ions do not react with water.
• A salt consisting of the anion of a strong acid and the cation of a weak base yields
an acidic solution because the cation acts as a weak acid and the anion does not
• A salt consisting of t