So far we have said nothing about how pH is detected and measured.
Acids have a sharp taste, and bases have a bitter taste, but this
method is both inexact and dangerous.
Bases feel slippery because they saponify, or make soap from the
oils of your fingertips, but testing for bases in this way can be
dangerous and is strongly not recommended.
Elaborate and convenient pH meters using glass electrodes provide
the most accurate means of measuring pH. The most common detectors,
however, are the color changes of acid-base indicators.
Methyl orange is red in acid
and yellow in base. The color tint shows the different extent of
delocalization of electrons in the two pH forms of methyl orange.
The extent of delocalization affects the wavelengths of light absorbed
and the color produced, as described in Chapter 9.