To determine the fluorides present in water.
Fluorides in excessive quantities and absence of fluorides in water, both create problems. A disfigurement in teeth
of humans known as mottled enamel or dental fluorosis is occured in those, who consume waters with fluoride
content in excess of 1.0 mg/L. It has been scientifically established that 0.8-1.0 mg/L of fluorides is essential in
potable water. Thus, absence or low fluoride content may cause dental caries in the consumers.
Fluorides are measured by colorimetric methods. Fluorides are separated out by distillation, if interfering
substances are present. Fluorides are analysed by a method that involves the bleaching of a performed colour by
the fluoride ion. The performed colour is the result of the action between zirconium ion and alizarin dye. The colour
produced is referred to a lake and the intensity of colour produced is reduced if the amount of zirconium present is
decreased. Fluoride ion combines with zirconium ion to form a stable complex ion ZrF6-- , and the intensity of the
colour lake decreases accordingly. The reaction is as follows: