Summary for rusting increase or decrease weight Discussion
Rusting increase or decrease the object's weight is the core question here: Priya P. asked whether an iron nail left in salt water for three days would weigh more or less after rusting. Several replies did not answer directly, instead urging her to run the experiment herself. Brian Terry gave the clearest guidance: weigh the nail, immerse it in salt solution, remove it after three days, dry it very carefully, and reweigh it so she can see whether it gains or loses mass. He also said she should then think through the chemistry of the reactions involved to explain the result, and offered to help if she posted the outcome. The thread does not give a definitive measured answer, but it emphasizes that the result depends on the experiment and on careful drying before weighing.
Q. Hello,
I was wondering if somebody weighed a iron nail before it corroded, left it in salt water for 3 days, and weighed it again after it had rusted, how would the weight change? I thought that it would either decrease as the nail has been eaten away by rust or increase as there is also a coating of rust on the nail … help me please, I don’t know which is right!
Priya P.
student – London
2007
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2007 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. Ken Vlach [deceased]
– Goleta, California 2007 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,
2007 ! 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. John Martin 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. Brian Terry |
A. Some of the iron is converted into iron oxide-rust. The oxide will weigh more than the iron did.
Some of the iron will become ferric or ferrous ions in the water giving you a slight loss.
The biggest problem will be the amount of water that the rust hydrates or mechanically retains. This will require drying at say 180 °F for 24 hours, then cooled and weighed.
It is going to take a good balance to be able to weigh to a tenth of a milligram and still be able to weigh the nail.
James Watts
– Navarre, Florida
Well just like to say thanks to whoever actually asked the question so I could find all your guys’ answers. And sometimes we don’t have 3 days… SO… yeah!
Sydney Carpenter
– Palmer, Alaska, USA
April 4, 2018