How does silicon dioxide react with NaOH and HF ?

Explanation

(a) With NaOH : Silicon dioxide reacts reacts with NaOH to form sodium silicate (Water glass)
` SiO_(2) + 2 Na OH overset ("Heat") to underset ("sodium silicate") (Na_(2) SiO_(3)) +H_(2) O`
(b ) With HF : Silicon dioxide reacts with hydrogen fluoride to form silicon tetra fluoride .
`SiO_(2) + 4HF to underset ("Silicon tetrafluoride ") (SiF_(4)) + 2 H_(2) O`