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I have a Chemistry question
Peter Principle
Registered User regular
Registered User regular
This may be a bone headed question, but it's something that I've always wondered about.
NaF dissolved in water is poisonous, but not nearly as bad for you as HF dissolved in water (hydrofluoric acid). In both cases, it's the Fluorine anion running around doing its thing, but why does it have such a different effect when the cation is H, as opposed to Na? Shouldn't an F- in solution be an F- in solution?
NaF dissolved in water is poisonous, but not nearly as bad for you as HF dissolved in water (hydrofluoric acid). In both cases, it's the Fluorine anion running around doing its thing, but why does it have such a different effect when the cation is H, as opposed to Na? Shouldn't an F- in solution be an F- in solution?
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Na is just Na, we eat that stuff like candy in our nasty American diets.
Maybe this is in reference to their states, though. HF is only distributed as a solution or a buffered mixture (a liquid), and if you get a little on your skin it's going to burn like an acid and get adsorbed pretty quick. NaF is a solid, is easier to weigh out and handle, and won't be as readily adsorbed through skin - but it's still something you DON'T want to touch!
In terms of ingestion, or even dissolution in water, HF's a pretty potent acid and NaF is fairly soluble in aqueous media. Both are going to liberate the fluoride ion quickly, the only difference being the acidity of HF vs. aqueous NaF - Which doesn't make a lick of difference in the body, considering the natural buffers / acids you'll encounter there will overpower small doses.
Not to disagree, but I'm fairly sure that Sodium Fluoride used to be used to fluoridate water and is sold as tablets to prevent cavitys.
edit:
I think it's the corrosiveness of HF which makes it a lot worse than NaF (fatal dose appears to be 5-10g according to the MSDS). So whilst the Fluorine might poison you, you'll get horrible chemical burns first.
Aside from the acidity hazards, I always thought the danger of Fluoride ions stemmed from two things. 1 - It's tendency to screw up your nerves. It's more dangerous than other acids in this regard not due to potency, but mostly because you don't even know it's hurting you because you can't feel it. 2 - It makes insoluble stuff in your blood. CaF2 and MgF2 aren't fun to have deposited in your tissues. Plus, your body is 'robbed' of these vital ions in the process.
Via wikipedia:
More seriously, once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. Burns with areas larger than 25 square inches (160 cm2) have the potential to cause serious systemic toxicity from interference with blood and tissue calcium levels. In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity. In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel or special rinsing solutions. However, because it is absorbed, medical treatment is necessary; rinsing off is not enough. In some cases, amputation may be required.
Hydrogen fluoride is generated upon combustion of many fluorine-containing compounds such as products containing Viton and polytetrafluoroethylene (Teflon) parts. Hydrogen fluoride converts immediately to hydrofluoric acid upon contact with liquid water.
HF is omgwtfbad because the HF bond is quite strong and thus it spends some time non dissociated. This allows it to dissolve through (penetrate) alot of the bodies non-polar fatty tissues etc. In comparision, NaF is purely ionic, and pretty much won't dissolve/penetrate the bodies fatty tissues.
HF's bond is small enough in 3-D space that it can just permeate through your outer tissue, whereas other acids would have to saponify your fatty tissues before reaching bone and bloodstream.
It's not necessarily the Ka value that allows HF to be so dangerous, but it certainly does help.
Wait, what? Can acids saponify?
I confused base-skin reactions and acid-skin reactions.