Does rusting increase or decrease the object's weight?

 I've often wondered about this myself, could you get a container and put salt water and a nail in it and post back in three days? I can wait for the answer.

 Ed. note: We especially like that one, Sheldon :-)

A. Corrosion by liquids is usually reported as metal weight loss per surface area per unit time (after cleaning off the corrosion). Use a household rust remover, as these contain inhibitors which prevent any additional loss of metal. See also letter #45169.

Many metallic materials are sold with coatings (varnish, metal plating, paint) which minimize corrosion. Corrosion testing can compare the efficacy of such coatings. When bare metal samples (usually flat panels, known area, uniform surface) are corrosion tested, a polished and cleaned initial surface is generally required to obtain data valid for comparisons.

A. If you remove the nail from the salt water, and somehow remove any remaining salt water, it will weigh more. Now you have the weight of the iron, plus the weight of the oxygen that combined with it to make the rust.

If you remove the rust, leaving only bare metal, it will weigh less. Now you have only the unreacted iron on the nail, that which combined with the oxygen to make the rust will have been removed.

Good luck with your project!

Cheers,

! If the test only takes 3 days why don't you try it yourself. In the time it's taken to receive this answer you could have had a result.

A. Priya,

The answer is to take a nail, weigh it, immerse it in salt solution for three days, remove it from the solution, dry it very carefully and reweigh it. That way you will have carried out the experiment yourself, would have worked out whether it loses or gains weight and so wouldn't have to crib off other people.

Once you have your result you will need to work out why you see either a gain or loss in weight. I don't know what year you are in (it sounds like somewhere between year 6 and 8) so I don't know how far you have got with chemistry but you need to look at what reactions are happening, that will then tell you why the nail gains or loses weight.

If, after you have done the experiment, you are still stuck then post your results and I will try to help, but I won't do your homework for you.