Ask A Scientist Chemistry Archive

  
name         Donald M.
status       educator

Question -   I was asked a question from  one of my 6th grade science
students concerning elements and I wasn't sure how to explain. He wanted
to know what the difference is in Iron that is on your automobile and the
Iron that you take as a vitamin or mineral supplement? Are these two
substances derived from the same natural element Iron (Fe)?
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Iron is used in the steel that goes into the car parts.  Humans also require
iron for our bodies to function properly.  They are both the element iron.
they might be bound differently to other things in steel vs. food, but it is
still iron.  If you want to have some fun, crush some iron-fortified cereal
and pass a magnet over the crumbs---tiny iron filings!  I did this when I
taught seventh grade science several years ago---you might find a lab at a
teacher web site.  It is a lot of fun and the kids are amazed!  Unless cereals
have changed since then, this should work.  I THINK I used Cheerios, but I am
not sure.
Pat Rowe
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In most cases, one is not talking about iron in its natural state (charge 
= 0). The iron in mineral supplements come in some formulation that is 
considered to be easily absorbed by the body (i.e. soluble, fits into 
biochemical cycles). The iron in a car is also a formulation (steel = Fe + 
C + other additives).

Greg (Roberto Gregorius)
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Absolutely they are the same element.
But the metal-elements look very different in compounds than they do in 
pure metallic form.
You have 3 states to consider: pure iron metal, mineral iron compounds, 
and biological iron compounds.

The iron in a car is about 100% Fe neutral atoms.  Certainly >90%, and the 
other elements mixed with it are also neutral atoms.
When iron is burned (possible, though not so easy) or rusted, it reacts 
with oxygen to become rust, Fe2O3, which is orange-red.
Oxygen is greedy for electrons, so this mineral compound is partially 
ionic: (Fe+3)2(O-2)3.
A (+) ion is an atom with some electrons stolen from it.  ("It does not 
bother me too much." some atoms say.)
A (-) ion is an atom that has more than its share.  ("So sue me." oxygen 
says.)
With its outer electrons stolen by the oxygen, the iron no holder has free 
electrons to trade with its neighbors,
so it cannot conduct electrically, so it can no longer be a shiny metal.
The native color of pure iron bulk ("Fe", with no + or -) is "70% 
reflective with no color bias",
  shiny metal color but noticeably a little darker than a silvered mirror.

The heart of each Fe+3 ion happens to have a natural red color,
because given white light, it likes to reach out and absorb blue and green 
light, but it leaves the red light travelling freely.

The iron in vitamins is in a compound, meant to add to the iron in 
hemoglobin molecules your red blood-cells.
Blood looks red for the same reason rust looks red: both have Fe+3 ions.

Black iron is the color of compounds with Fe+2 ions instead of Fe+3;
these are iron-oxide compounds not quite completely reacted to the 
finishing point.
Similarly, blood with less oxygen stops being red, is instead dark dull 
bluish.

The Fe+3 ions in some iron compound in your vitamins is present in only a 
few percent concentration.
And it's a compound, like salt or ash, instead of an electrically 
conductive mass of 100% neutral iron atoms.
Such a low percentage might not be enough to give the inside of the pill a 
reddish tint.

A couple of reasonable sensory demonstrations might be to burn steel wool, 
or burn soda-pop cans.
Such cans are aluminum metal, very shiny and cool.  After burning they are 
a very flaky white ash.
Both require applying extra heat with a flame.  Perhaps a propane torch 
would do.

Jim Swenson
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