Acetic acid is an organic acid, but behaves in a similar way:
Because acetic acid is so common, it is often given the shorthand
representation HOAc, with Ac- symbolizing
The dissociation is then written
The acid-dissociation equilibrium constant is
In such expressions concentrations of ions and molecules are always
given in units of molarity (M), or moles per liter of solution.
The units of Ka are unmistakable, and ordinarily are
omitted.
Ammonia is an example of a weak base that reacts with water to
yield ammonium and hydroxide ions, but the reaction is far from
complete:
Water is both solvent and reactant in this reaction. For moderately
dilute solutions of ammonia, the concentration of water will not
change appreciably from that of pure water:
For simplicity, the constant H2O concentration of 55.5
moles per liter can be brought to the left side of the equation
and incoroporated into the equilibrium constant: