JEE Main 2014 · 9 Apr · Shift 1 · Chemistry Q42

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ChemistrySingle correct+4 / -1Question 42 of 90

The gas evolved on heating $\ce{CaF2}$ and $\ce{SiO2}$ with concentrated $\ce{H2SO4}$ , on hydrolysis gives a white gelatinous precipitate. The precipitate is :

hydrofluosilicic acid

silica gel

silicic acid

calciumfluorosilicate

Answer and worked solution

Official answer: C

$\ce{2CaF2 + SiO2 + 2H2SO4 -> SiF4 ^ + 2CaSO4 + 2H2O}$ . Hydrolysis then gives the white gelatinous precipitate, silicic acid:
$\ce{3SiF4 + 4H2O -> H4SiO4 v + 2H2SiF6}.$

Topics:Group 14

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JEE Main 2014 · 9 Apr · Shift 1, Chemistry question 42