Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Polleke on December 26, 2012, 01:16:38 PM
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Fe2+ vs Fe3+
I wonder why Fe3+ is not as soluble as Fe2+?
Is there an explenation for this or is it something that has been demonstrated but net yet explained why this is the case?
thanks in advance.
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It probably has something to do with acidity since Fe+3 is more acidic than Fe+2, and Fe+3 salts are only soluble below a certain pH (water's pH of 7 exceeding this certain pH) while Fe+2 is more basic and is soluble below a higher pH.
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This is something you would not need to understand at the freshman level. If you take inorganic chemistry, you will learn an important formula z^2/r, where z is the charge and r is the radius of the atom. We use this ratio to determine acidity. You can look up this information online if you are interested and you will find the one with the larger ratio is the most acidic. If it is more acidic, it will dissolve more (least acidic will remain relatively unchanged as a hydrated ion) and hydrohalic acids, oxo acids, and oxo anions will form. Again, not something you really need to understand at the freshman level... probably more of a memorization thing for you.
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This is something you would not need to understand at the freshman level. If you take inorganic chemistry, you will learn an important formula z^2/r, where z is the charge and r is the radius of the atom. We use this ratio to determine acidity. You can look up this information online if you are interested and you will find the one with the larger ratio is the most acidic. If it is more acidic, it will dissolve more (least acidic will remain relatively unchanged as a hydrated ion) and hydrohalic acids, oxo acids, and oxo anions will form. Again, not something you really need to understand at the freshman level... probably more of a memorization thing for you.
I am not a chemistry student, so I need to look it up myself, if I want to understand it or at least know why one will dissolve and the other not.
Do you perhaps know a good website where I can find more information?
Are there for example websites that show you the charge and radius of the atoms?
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http://periodictable.com/Properties/A/AtomicRadius.v.html
that link shows atomic radii of atoms.
The charge is given to you since it's an ion... Ex: Fe 2+, the charge is 2+, and Fe 3+, the charge is 3+. If they don't give you a charge, it's not an ion so the charge is 0.
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http://periodictable.com/Properties/A/AtomicRadius.v.html
that link shows atomic radii of atoms.
The charge is given to you since it's an ion... Ex: Fe 2+, the charge is 2+, and Fe 3+, the charge is 3+. If they don't give you a charge, it's not an ion so the charge is 0.
The charge part, ok, I did not need to ask that lol ;D
The websites gives the radium of the neutral element I see, but how can you know the charge of the ions?
The more electrons are gone, the smaller the radium, but how can you know this radium (the exact number) ? Is there a way to calculate this or ?
I see iron has 156pm, but how much is that for Fe2+ or Fe3+?
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Try looking up the ionic radii. There should be something on the internet that gives the radii for the most common ions of each element. They usually give lists in textbooks if you have one.
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But for the formula z^2/r, you're not using the ionic radii... you're using the radii of the free element.
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But for the formula z^2/r, you're not using the ionic radii... you're using the radii of the free element.
Oh ok,so for both Fe2+ and Fe3+ I need to use the same radii, 156pm, in the formula you gave me?
Correct?
If this is the case, then its +- doubling the acidity.
I can not really imagine this is such a big difference?
2^2/156 compared with 3^2/156 is 0,025 vs 0,057
I do find it strange that you would use the radii of the free element and not the radii of the ions, since do you want to calculate the acidity of the ions.
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Oh ok,so for both Fe2+ and Fe3+ I need to use the same radii, 156pm, in the formula you gave me?
Correct?
I am not entirely sure what butlerw2 means. Each ion has its own radius and I would assume you have to use those.
Thing is, it will give the same general result, as radius of the cation goes down with the positive charge (so the ratio will grow even faster than if used with the same radius value).
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Oh ok,so for both Fe2+ and Fe3+ I need to use the same radii, 156pm, in the formula you gave me?
Correct?
I am not entirely sure what butlerw2 means. Each ion has its own radius and I would assume you have to use those.
Thing is, it will give the same general result, as radius of the cation goes down with the positive charge (so the ratio will grow even faster than if used with the same radius value).
Indeed, perhaps thats why you need to use the radius of the free element.
It seems its harder that I assumed to say something about why an element is less/more soluble.