corrosion rate experiment

Question

i am doing a science experiment on how different liquids affect the corrosion rates on a steel nail in water and salt water. After a couple days the nail had a orange substance layered on it ( i thought it was rust). By day 7 it would layer on the nail and fall off ( wasn't stuck on). when i weighed the nails they don't drop by much in mass ( 0.04 g ) . most of the substance fell off and collected at the bottom . What do you think the orange substance on the nails were? how did it form when not much mass was lossed by the nails?

i also want to ask what the chemical formula of corrosion with steel ? and what metals are steel made out of?

Answer 1

The orange stuff is indeed rust, Fe₂O₃^. H₂O. Since you have a surface reaction and not a reaction in solution, it will take a while to react the entire nail. The iron content in the rust is 62.85% by mass, so a little over half. Losing .04 g of the Fe off the surface of the nail means you created about 0.064 g of rust.

 

Most nails are not made of high quality steel. Some nails are treated with zinc (galvanized by dipping in molten zinc) to slow down corrosion. I wouldn't think yours was, although most of them at least have a thin coating of oil to keep them from developing corrosion before they can be sold.