Hydrofluoric acid

At work we have a large tank that is comprised mostly of hydrofluoric acid, I don't know the dilution factor as I'm not the one making the bath, but I have a question, when emptying the bath we tried to check if acid really is heavier then water, when we insert the pH stick, it comes up "acid", but the stick itself only goes about 2cm into the bath, where theoretically the water would be, we emptied half of the bath so the acid would be emptied and tried again, same result, is the acid mixed completely with water or is it just stronger near the bottom of the tank?




Liquids with unlimited miscibility with water, like ethanol, sulfuric acid and hydrofluoric acid do have different densities than water. This may lead to layered state, if one liquid is intentionally and carefully layered over or under water, or if there was just insufficient mixing.


If mixed properly, what takes quite short time with proper mixing, the solution of such liquid gets homogeneous, without separation tendency. Therefore, there is no reason to expect variation of the acid concentration, unless it was locally and significantly spent due the bath purpose and not mixed afterwards.


If there is such local acid spending then the result depends on how the liquid density changes by the process. If it decreases, it would have tendency to trigger convective raising stream and vice versa.


BTW, people without sufficient knowledge about dangerous chemicals should not be around them. A sudden splash of hydrofluoric acid on skin can painfully kill a person within not many hours. A part of danger is the acid takes its time for skin penetration before the person starts to observe dooming symptoms. Chemistry of fluorine had already too many victims, especially in first decades after the element discovery.


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