Acidity and Basicity,

the pH scale.

There are strong Acids and strong Bases. Acids are commonly known to corrode (eat away / burn) materials, Bases have the same effect. However Acids and Bases are opposite, that is an Acid and a Base cancel the effect of each other and become neutral.

The pH of a substance represents its acidity (or basicity). A solution may have a pH of 9, note there are no units. A pH of 1.5 describes the acidity of a solution as 5 meters describes the length of an object.

All acids have a pH < 7 and bases a 7 < pH < 14. The pH scale goes from 0 to 14, 15 steps in total, the middle step 7 is said to be neutral, that is it has very little desire to react with other substances.

Acidity is a function of the amount of hydrogen ions (H+) present in a solution. pH equals the negative logarithm of the hydrogen ion activity (see also detailed description). Most pH measurements are made in solutions where the pH falls between 0 - 14 pH.

The pH of a solution is a very important characteristic. It determines which chemical reactions can occur and how efficiently they will occur.

The only other parameter with such importance is temperature.

H/W pg 221 Exploring Science, Q 1 - 7

The measurement called pH was originally used by the Danish biochemist S.P.L. Sørensen in 1909, while working on beer quality for Carlsberg, to represent the hydrogen ion concentration of an aqueous solution.

the pH of a variety of common substances


Kawah Ijen volcano Crater lake 1km across, and its water has pH of 0.5

We could also use the Hanna pH meters

use this to calibrate them.