Question

Why do we not use sintered glass frits with hydrofluoric acids? Why do not collect silver halide precipitates on glass frits?

Answer 1

Concentrated `HF` actually dissolves glass, and would make fairly short work of a sintered glass disc.

Explanation:

`SiO_2 + 6HF rarr SiF_6^(2-) + 2H_3O^+`

I have seen this done in a laboratory: someone, unwisely, using a frit with conc. `HF`; it can be done once or twice. Of course, the next time some punter uses that frit, it has been severely weakened, and then breaks - of course, that will be the time when they are trying to filter a small quantity of a compound that they have taken weeks and many steps to prepare.

The above reaction is the reason why hydrofluoric acid is supplied in PLASTIC winchesters rather than glass ones.

Precipitates of silver chloride are usually very finely divided, and it would take a long time (+24 hours) to filter such materials - silver halides are also photosensitive, and would rapidly reduce.