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Corroding nails lost no weight

hi I am a student in 10th grade in Australia. I have a question

I did an experiment where I had 5 test tubes with saturated salt water in one, tap water in one, sea water in one, distilled water in one and 1g of salt in one. The amount of water in each of the test tube is the same -- 5mL. the nail I put in it to rust weighed 1.01g. After 3 weeks my group and I took the nails out of the water and used steel wool to take off any rust. then we measured the nails and they weighed the 1.01! -- exactly the same as before. Why is this? thank you

George R [surname deleted for privacy by Editor]
student - Sunnybank , QLD , Australia
November 21, 2010

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Possibly the largest mistake that you made was not drying the nails in an oven or heated dessicator.
A 1 gram nail is fairly small and 5 ml of liquid would have covered most of the nail (I think). Since it takes oxygen to form rust, so a lesser amount of water might have worked better. A larger nail that has been steel wooled to remove all oxides. platings and spray on coatings would have been even better. I would have capped the tubes to keep out CO2.
The answer to your question is in the fact that the rust pits steel and even tho you steel wooled the nail to remove surface rust, you had water in the pits and relative to the rust, it is heavy as it fills the pit. Also, a trace amount of the steel wool will become embedded in the nail, adding some weight.

James Watts
- Navarre, Florida
November 22, 2010