The acidic, basic or neutral character of any solution can be expressed by expressing its H+ ion concentration. A Danish biochemist Peter Sorensen suggested a method of expressing the concentration of H+ ions in terms of pH. In Danish language, pH stands for protenz de HYDROGEN which means power of H+ ions. pH of a solution is given by

pH = -log [H+] = log 1[H+]

where [H+] = concentration of hydrogen ions in solution.

To report the pH, a SFOR an acidic solution, pH is less than seven.

For a basic/alkaline solution, pH is greater than seven.

For a neutral solution, pH is equal to seven.

The pH of a solution is measured accurately using an apparatus known as pH meter. An approximate value of pH can be obtained by using universal indicator/pH paper.

Indicators: are the SUBSTANCES which change the COLOUR at a certain pH. Some common examples of indicators are litmus, phenolphthalein and methyl orange. Out of these, litmus is a NATURAL indicator while phenolphthalein and methyl orange are synthetic indicators. cale from 0 to 14 was devised.