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Measuring rust, chemical formula for rust


I am currently doing a science fair project about rusts forming on metalloids. I already have read about measuring rust by weight. On the bottom of that letter, it read

"Once you know how much rust there is, and the chemical formula for rust, you know how much iron had to rust away to produce that much rust." Is the "how much" part measured in weight? What is the chemical formula for rust?

If someone could please could inform me the answer to these questions, I would much appreciate it.

Thank you,

Samuel J. [last name deleted for privacy by Editor]
student - Glendale, Wisconsin



There are, I was taught, two species of rust. a) Fe203 and b) Fe304 ...

What the difference is, I dinna ken. I sure have forgotten!

This might be of some help, I dunno.

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(It is our sad duty to advise that Freeman passed away April 21, 2012. R.I.P. old friend).

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Red rust is Fe203, and black rust is Fe304.

paul morkovsky
Paul Morkovsky
- Shiner, Texas, USA


I'm just wondering about this question. The student wants to investigate "rusting on metalloids". Technically speaking, rust is formed by the combination of oxygen with iron. Iron is not a metalloid. Did you mean oxidation of the metalloids?


Josephine Demerre
PSJA High School - Pharr, Texas


Good observation, Jodem, but my bet is that Samuel probably meant metals but wrote metalloids.

Ted Mooney,
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Ted Mooney, P.E. RET
Pine Beach, New Jersey



I am currently in 7th grade. I'm doing a science fair project on how rust is formed, and my teacher said that I needed to show her the actual equations.

She doesn't want the formulas like Fe2O3 and Fe3O4, so does anyone know what "equations" she might be talking about?

Please answer A.S.A.P


Kassandra [last name deleted for privacy by Editor]
student - Virginia, United States


I would have thought that chemical equations were beyond your grade level, Kassandra, but maybe you are advanced.

An example of a chemical equation might be:

4Fe + 302 => 2Fe2O3

This means that 4 atoms of iron combine with 3 molecules of oxygen gas to yield 2 parts of Fe2O3 rust. It's an "equation" because an equal number of atoms of iron and oxygen are on each side of the arrow.

Ted Mooney,
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Ted Mooney, P.E. RET
Pine Beach, New Jersey

July 13, 2008

I am a teacher of 5th and 6th grade science and just wanted to share that at a very rudimentary level, understanding balanced chemical equations and how to read them is part of my curriculum. The basic rust statement and water to oxygen & hydrogen are a standard that I use in my teaching. I will give a page of about 20 unbalanced statements for those of my 5th graders who are up to the challenge. It is amazing what an 11-12 year old can do when given the chance. Understandably, this is a very small part of my curriculum as it is definitely above the developmental level of some students. But, to say that it is above today's 7th grader may not be an accurate assumption. Now, if you were talking about when I was a 7th grader, I would have to agree. I don't remember coming close to this until high school chemistry.
Sorry, about the slightly off topic, but I felt it prudent to respond.

Kevin Gallagher
- Northridge, California

July 25, 2008

Responding to the first question above, if you are looking for a measurement based on atoms and atomic weight, most likely you are going to find your measurement in terms of moles. Unfortunately, it's been about 6 or 7 years since college chemistry, so I can't remember how to calculate moles... but you should be able to find information on this either online or at your school.

Dustin Bunch
- Lebanon, Ohio

September 11, 2008

I am currently a student in fifth grade. Just wondering, why isn't there hydrogen in rust?

Ruoqi W [last name deleted for privacy by Editor]
- Miami, Florida

September 18, 2008

Sorry, but I don't quite understand your question. There is no hydrogen in rust, because that's not what rust is. But maybe I don't really understand what you are trying to get at? Maybe we should say that it's not really the water (H2O) that reacts with the iron to form rust; rather it's the oxygen in the air or dissolved in the water that reacts with the iron?


Ted Mooney,
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Ted Mooney, P.E. RET
Pine Beach, New Jersey

December 1, 2008

I'm doing a science fair on the rusting of steel nails, iron nails, and copper nails. Can someone explain what that formula for rust REALLY means because I just don't get it.


Will C [last name deleted for privacy by Editor]
- Cockeysville, Maryland

December 2, 2008

Hi, Will. Your librarian can help you find an age-appropriate book on chemistry and corrosion for your science project. You didn't say what grade you are in, what science or chemistry you've had yet, and what terms and concepts you do understand as a starting point. The internet is great for a lot of things, but not very good as a tutorial learning aid :-(


Ted Mooney,
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Ted Mooney, P.E. RET
Pine Beach, New Jersey

July 4, 2011

I have been led to believe that the chemical equation of rust is 4Fe + 3O2 + 6H2O= 4Fe(OH)3 or is there some form of rust we all have not been told?

Jack S.
- Sydney, NSW, Australia

November 11, 2011

is there any photo for this equation for the makeup of rust? I'm in 6 grade and can't find any atomic resemblance on our textbook.

Daniel L
- Coppell, Texas, US

November 14, 2011

Excellent question, Daniel.

Although the formula for red rust is Fe2O3, that is, a molecule of rust consists of 2 atoms of iron and 3 atoms of oxygen, I wasn't able to find a "stick figure" of the molecule either.


Ted Mooney,
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Ted Mooney, P.E. RET
Pine Beach, New Jersey

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