1. IES Auringis. Jaén.
José Cayetano Bautista Expósito
4º ESO. Physics and Chemistry. Unit 8 (II).
pH.
● pH is used to measure the acidity or basicity of a solution. The pH
measurement represents the tendency of hydrogen ions to interact
with other components of a solution.
●
Pure water(25ºC)
,considered neutral (not an acid and not base), is
pH=7 .
● Acids have pH numbers lower than 7.
● Basic (alkaline) solutions have pH numbers higher than 7.
● pH measurements are important in many fields as biology, chemistry,
medicine, civil engineering (concrete behaviour), etc.
● Measured pH values are between 0 (strong acid) and 14 (strong
alkali).
● Accurate measurements of pH can be obtained by electronic devices
called pH-meters, that measure the pH values using the electricity of
the ions in a solution.

2. IES Auringis. Jaén.
José Cayetano Bautista Expósito
4º ESO. Physics and Chemistry. Unit 8 (II).
pH.
● And approximate measure of
pH can be done using
different types of chemical
indicators that change its
colour according to the acidity
or basicity of a solution.
● Universal indicator paper is
paper that have been
impregnated with a mixture of
indicators to achieve a
continuous colour change
from about pH 2 to pH 10.