The gas evolved on heating CaF 2 and SiO 2 with concentrated H 2 SO 4 , on hydrolysis gives a white gelatinous precipitate. The precipitate is:

Step-by-step solution

Reactions involved are CaF 2 + H 2 SO 4 Conc . → Δ CaSO 4 + 2 HF g SiO 2 + 4 HF g → Δ SiF 4 g + 2 H 2 O 3 SiF 4 + 2 H 2 O → 2 H 2 SiF 6 + SiO 2 The mixture after hydrolysis apperas as white gelatinous precipitate.