dgm
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Why are some salts more toxic than others?
For instance, I'm particularly puzzled by the fact that ferrous chloride is considered to be significantly more toxic than ferrous fumarate (NFPA
level 3 vs level 1), which is used as an iron supplement.
Clearly the body is perfectly capable of handling both Fe2+ and Cl- ions, because we get them from eating foods all the time,
right? So taking FeCl2 in aqueous solution shouldn't be terribly toxic, theoretically?
[Edited on 2013-6-6 by dgm]
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chemcam
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What!? FeCl2 is corrosive, you would be drinking HCl if it was in solution.
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dgm
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So FeCl2 forms HCl in solution, but NaCl does not? If so, why?
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woelen
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FeCl2 is not that toxic, FeCl3 is more so. Indeed, FeCl3 forms HCl in solution and is quite corrosive. This is because iron(III) ions are very prone
to hydrolysis.
Iron(III) ions form a complex with water: [Fe(H2O)6](3+). This better can be written as [Fe(OH2)6](3+), the oxygen atoms coordinate to the iron atom.
The oxygens are fairly tightly bound and electrons are drawn fairly strongly inside this structure, making the outer sphere of this complex ion having
a fairly strong positive charge. This makes the O-H bonds in the water weaker and if another water molecule moves close to this complex ion, then a
H(+) ion easily transfers from the complex ion to the free water molecule:
[Fe(OH2)6](3+) + H2O ---> [Fe(OH2)5(OH)](2+) + H3O(+)
This is a somewhat simplified description of what really happens, but it describes the essential of the mechanism. So, the liquid in which the FeCl3
dissolves become squite strongly acidic.
This corrosiveness exists for ferric nitrate, sulfate, chloride and many other simple anions. With other anions (e.g. citrate, fumarate, acetate,
cyanide) the effect is much weaker or even completely absent, because the iron forms complexes with these ions, which are very tightly bound and hence
no water molecules are connected to the iron atom and no hydrogen ion can transfer from the complex ion to water molecules around.
With iron(II) this effect is weaker than with iron(III).
[Edited on 6-6-13 by woelen]
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dgm
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Interesting! Thanks a lot. I'm sure this will make much more sense to me once I've learned a bit more about chemistry.
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Random
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FeCl2 is not that toxic but I could bet that it's gonna be converted to corrosive FeCl3 in contact with O2 without reducing agent.
Also some salts are more toxic than others just because of their nature. Corrosive chemicals act upon protein tissue for example and denature and
destroy it. While heavy metal salts are also capable of this, some may be inhibitors of some enzymes or processes inside our body. Now where all of
this leads depends entirely on the damage that has been done, mercury for example will often damage nervous system.
Corrosive chemicals are often dangerous by their concentration.
[Edited on 10-6-2013 by Random]
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woelen
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FeCl2 does not produce FeCl3 when it comes in contact with oxygen. Instead, a basic chloride is produced, which is a mixed chloride/oxide, or a mixed
chloride/hydroxide when air is somewhat humid. This basic chloride is insoluble in water and hardly is corrosive.
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AJKOER
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Now, implied in your question on toxicity is toxic to humans specifically.
The point is important and revealing, as for example, soluble copper salts are highly toxic to small animals including cats, dogs, rats, .., fish,
fungus,..., than to humans. Silver salts have been used to treat burns before antibiotics.
So part of the answer to your question may be that the level of toxicity is relative to aspects of the specific biochemistry of the living entity
(where is a biochemist when you need one).
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Random
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Quote: Originally posted by woelen  | | FeCl2 does not produce FeCl3 when it comes in contact with oxygen. Instead, a basic chloride is produced, which is a mixed chloride/oxide, or a mixed
chloride/hydroxide when air is somewhat humid. This basic chloride is insoluble in water and hardly is corrosive. |
I was wrong then, read somewhere that bubbling air through FeCl2 will produce FeCl3. Seems like it was not true. Thanks for the explanation.
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