How do you measure rust on nails?

Question

I am not sure on how to measure the rust on nails. Is it possible to scrape the rust off and measure the rust on a scale? Also does the weight of a nail increase or decrease when rust forms on it?

Answer 1

The best way would be to weigh the clean, unrusty nail first; then re-weigh periodically as it gets rusty. The new weight will be larger as it will be the weight of the nail + the weight of the combined oxygen in the rust.

Note this will only work in cases where all the rust stays attached to the nail (light rusting) If you are measuring heavy rust which is scaling off, have the nail in a small, light weight container so you don't loose anything.

If you are trying to monitor the oxidation of steel, you might get better results using steel wool; because of the higher surface area, the weight change will be much larger in proportion to initial sample weight, so easier to observe changes. Just remember steel wool is usually coated with oil (to avoid rusting) so clean it with hexane or other solvent first.

Answer 2

Since a metal combines with oxygen when it rusts, the metal should get heavier.

The easiest way to perform your experiment is to simply weigh the nail at different time intervals to see how much weight it gains. You need to have an analytical balance, since the weight gain for a single nail is going to be very tiny over the short term. Maybe you might consider taking a bunch ( 20 or so) nails to make the weight gain more detectable.

Answer 3

If you want to know how much of the nail's iron was lost to rust you should weigh the unrusted nail, then weigh it again after it has rusted and finally scrap off as much rust as possible and weigh again. The difference between the new nail and the scraped nail tells you how much of the iron was "lost". The difference between that figure and the weight of the rust will tell you how much of the rust's weight is from oxygen.