Lectures on pH calculation

Contrary to what many textbooks do I decided to make an experiment and to start from the most general cases down to more and more simplified. I wanted to underline the fact that all equations used for pH calculation are in fact simplified cases of the general approach. Whether I succeeded I have no idea. Your comments are welcomed.

English is my second language. Preparing these materials I felt like carving concrete with a stick. If you spot any language errors please feel free to drop me a line.