I moved the following sentence from the main article here:
- In fact, both blood and the planet Mars get their reddish hue from oxidized iron (rust).
I am not sure this is correct. First of all, hemoglobin is red whether it contains oxygen or not. Second, if it contains oxygen, then it contains molecular oxygen (O2) and not oxydized iron. Could somebody with a firmer grasp on these things please confirm? --AxelBoldt
Yeah I think this is correct. Oxygen is bound to the Haem groups in haemoglobin chains to form oxyhaemoglobin (HbO8:
Hb + 4O2 -> HbO8
Although 'oxidized' may not be so chemically correct (I don't know about loss of electrons) they are loosely bound and not in the 02 form.
Do you think the original statement, claiming that blood is red because of oxidized iron, is correct, or that my statement above is correct? --AxelBoldt
original statemen -- sodium
Well, I don't understand your argument. What are you claiming actually causes the red colour of haemoglobin? As far as I know, haematite is red because of the Fe3+ ions. Haemoglobin (both oxy- and deoxy-) has Fe2+ ions - the iron is not oxidized by the binding of oxygen. Fe2+ ions cause a yellow-green colour, I think, so they can't be what makes haemoglobin red. Unless I've got something wrong here, the original statement is at best very misleading. --Zundark, 2001 Oct 8
The color of an ion depends on its environment. In aqueous solution ferric irons (Fe3+) are coordinated with six water molecules and have a yellow color rather than the reddish color of hematite, where they are coordinated with six oxide ions, while the anhydrous chloride is greenish. Fe2+ are green in aqueous solution but that doesn't say much, the presence of nitrogen and oxygen (only oxyhemoglobin is bright red) are going to affect the color significantly. The iron is definitely what is responsible, though, and most brightly colored compounds are made so by coordinated transition metals. Someday we should have an article on ligand field theory.
How about the following statement:
- "Both the red color of Mars and the red color of blood are caused by an interaction of oxygen and iron."
That avoids the term "oxidization" which is not involved in hemoglobin if I understand it correctly. --AxelBoldt
Have some questions about this statement
In most if not all human languages, "red" is the first color name developed after "black" and "white."
I'm not sure what this means. Does it mean that ten thousand years ago, people only talked about black and white and then someone invented the word red? Or does it mean that babies learn to identify red after they identify black and white.
It's not obvious to me that we know enough about the development of language to make the first statement. If the second is true they it should be expanded.
- Here's the story. I don't have a citation right wth me, but it's a fairly standard linguistic thing. A survey of a large number of languages revealed the following:
- -All languages had terms for black and white.
- -If a language had three terms, it had a term for red.
- -If a language had four terms, it had a term for either yellow or green.
- -If a language had five terms, it had terms for both yellow and green.
- -If a language had six terms, it had a term for blue.
- And so forth. I'll try to get a cite and expand on it - it could be an article. - montréalais