Question

hydrofluoric acid is used for etching of glass.why?

Answer 1

Etching is the process of introducing a printed or designed surface on the glass by making the surface little bit rough. This process is possible only if the SiO₂ glass is allowed to have some changes in the amorphous structure. For such process hydrofluoric acid is the best acid as it contain Fluorine atom which is having highest affinity toward electrons i.e it is one of the best electronegative atom known. This electronegativity of fluorine allow it to displace electronegative oxygen atom from Si-O bond by Fluorine atom and change the property of glass.

Reaction involved :

SiO₂ + 6HF > H2SiF₆ + 2H₂O

Formation of complex hydrofluosilicic acid make the surface rough and flexible for the printing and designing using some metal like Cu . Since no such electronegative element have the ability to replace Oxygen atom from Si-O bond. Thus hydrofluoric acid is used for etching of glass