Question

Hydrolysis of SiF4 in alkaline medium produces

Answer 1

The most characteristic reaction of silicon tetrafluoride is that with water, by which gelatinous silica and hydrofluosilicic acid (H2SiF6) are formed. The first reaction is one of hydrolysis: 

SiF4 + 3H2O = H2SiO3 + 4HF; 

but this hydrolysis is not perfect, for silicon tetrafluoride combines with hydrogen fluoride to form hydrofluosilicic acid, H2SiF6, which can exist in aqueous solution: 

2SiF4 + 4HF = 2H2SiF6; 

consequently the complete reaction is 

3SiF4 + 3H2O = H2SiO3 + 2H2SiF6. 

Hence it will be understood that when silicon tetrafluoride is passed into a concentrated solution of hydrogen fluoride, hydrofluosilicic acid is formed without separation of silicic acid. 
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