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  4. The gas evolved on heating CaF2 and SiO2 with concentrated H2SO4, which on hydrolysis gives a white gelatinous precipitate. The precipitate is:

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Q. The gas evolved on heating $CaF_2$ and $SiO_2$ with concentrated $H_2SO_4$, which on hydrolysis gives a white gelatinous precipitate. The precipitate is:

JIPMERJIPMER 2018The p-Block Elements

Solution:

Reactions:
$H _{2} SO _{4}+ CaF _{2} \rightarrow Ca \left( HSO _{4}\right)_{2}+ H _{2} F _{2}$
$2 H _{2} F _{2}+ SiO _{2} \rightarrow SiF _{4}+2 H _{2} O$
$SiF _{4}+ H _{2} O \rightarrow H _{2}\left[ SiF _{6}\right]$
$H _{2} SiF _{6}$ is hydrofluorosilicic acid.