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I'm looking into conducting an experiment on the adsorption of fluoride (for my International Baccalaureate Extended Essay). As I will be investigating the role of $\mathrm{pH}$ in adsorption capacity, I will be dealing with $\ce{NaF}$ solutions of varying $\mathrm{pH}$. Could hydrofluoric acid be created by this process, and could it be dangerous in the dilute concentrations I am dealing with (<$0.5\ \mathrm{g\ L^{-1}}$)?

My reasoning is that added $\ce{H+}$ will move the equilibrium of the buffer $\ce{F^{−}(aq) +H3O+(aq) <=> HF(aq) + H2O(l)}$ to the right, and the $\mathrm{pH}$ will hardly change until the buffer capacity is exceeded. I'm still not sure whether this poses a health risk, though.

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    $\begingroup$ related chemistry.stackexchange.com/questions/51223/… $\endgroup$
    – Mithoron
    May 26, 2016 at 21:36
  • $\begingroup$ (Soluble) fluorides are always poisonous, only the undissociated, relatively non-polar HF (i.e. fluorides under acidic conditions) quickly penetrates the skin. $\endgroup$
    – Karl
    May 27, 2016 at 11:49

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Your reasoning is correct. Solutions containing dissolved fluoride salts can form HF under acidic conditions. I personally would not take any chances with exposure, because even dilute concentrations of HF can cause severe burns if enough of your skin area is exposed to it. Standard PPE would include goggles, faceshield and neoprene gloves. PVC sleeves and lab apron are recommended as well.

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    $\begingroup$ HF does NOT cause visible or even tangible burns on the skin, unless highly concentrated, and even then much less than ordinary hydrochloric acid. The effect is one of intoxication of the body parts below the affected skin part, followed by systemic intoxication. $\endgroup$
    – Karl
    May 27, 2016 at 11:38

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