Question

Why is HF not stored in plain glass bottles?

Answer 1

HF is a weak acid still it is capable of reacting with glass. This is because of the fact that HF reacts with SiO₂ to form [SiF₆]^2- ions which is quite stable.
Hence, in order to store HF we use wax coated glass bottles.
The equation for above reaction is as follows:

SiO₂ + 6HF → [SiF₆]^{2 -} + 2H⁺ + 2H₂O