Rust in test-tubes of HCl FeO or Fe3O4?

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Experiments involving steel nails in hydrochloric acid (HCl) solutions with a pH of 1.5 to 2 reveal that the rust formed is black and settles at the bottom of the test-tube, suggesting the presence of FeO or Fe3O4. The difference in rust color and attachment to the nails when using salt solutions, where the rust appears red and adheres to the nails, is attributed to the oxidation state of iron ions. In HCl, higher concentrations of Fe2+ ions may not have sufficient time to oxidize to Fe3+, resulting in the formation of black rust. In contrast, salt solutions likely promote the oxidation to Fe2O3, which is red and adheres to the surface. The discussion highlights the role of coordination chemistry and Crystal Field Theory in explaining the color variations based on the ligands surrounding the iron ions.
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rust in test-tubes of HCl FeO or Fe3O4??

I am doing experiments on steel nails in HCl solutions with a pH of about 1.5 - 2.
The rust is black in colour, and is not attached to the surface of the nails. It stays at the bottom of the test-tube. Is this FeO or Fe3O4. Why is it that the rust I am getting in solutions of just salt is not the same colour?. And why is it red and attaching to the nail?
 
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prime-factor said:
I am doing experiments on steel nails in HCl solutions with a pH of about 1.5 - 2.
The rust is black in colour, and is not attached to the surface of the nails. It stays at the bottom of the test-tube. Is this FeO or Fe3O4. Why is it that the rust I am getting in solutions of just salt is not the same colour?. And why is it red and attaching to the nail?

It has a lot to do with coordination inorganic chemistry which depends on quantum mechanical explanations which relate the iron to the " field " of ligands around it to explain the color , you may want to start off with Crystal Field Theory.
 


prime-factor said:
I am doing experiments on steel nails in HCl solutions with a pH of about 1.5 - 2.
The rust is black in colour, and is not attached to the surface of the nails. It stays at the bottom of the test-tube. Is this FeO or Fe3O4. Why is it that the rust I am getting in solutions of just salt is not the same colour?. And why is it red and attaching to the nail?
Maybe with HCl you get more Fe2+ ions, that don't have enough time to be oxidized by air oxygen into Fe3+. In the first case you would get FeO (black), in the second Fe2O3 (red).
 

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