Derivation .... The "acidity ladder" gives a visual representation of the relative acidity of common organic functional groups and provides an alternate method to recalling pKas rather than memorising the numbers in a table. The position on the ladder can be helpful in rationalising or predicting the reactions of acids and bases. We will talk about how to use the ladder in the next few pages... We will also investigate the factors that contribute to the relative acidity of the groups represented on the ladder.

Rather than memorising absolute values, having a good knowledge of the general order of pKas can often be good enough, more than enough in fact..... and fortunately, the most important pKa values can often be rounded off to the nearest "5".... (the rungs of the ladder)

The ladder shows the approximate pKa of the corresponding acid, for example, the pKa of water is about 15 (actual value = 14) corresponding to the reaction H2O <=> H+ + HO-.

When using the "ladder" make sure that you are considering the right acid (especially for systems like water and amines) since they have two equilibria and both appear on the ladder. -

There are (of course) other functional groups that could be included. Feel free to print it out and add more values if you feel the need.

The functional groups represented on this version of the acidity ladder are the more common ones and help reveal some of the key general trends based on structural factors.