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topic 43606

Do coins rust faster in salt water or fresh water

A discussion started in 2007 & continuing through 2017


Q. Hi, my name is Donald and I in the 3rd grade. I want to known because I did it. I put a nickel in a cup of salt and another one in fresh water for about five days and I don't see nothing happening so I want make sure I didn't do nothing wrong.

Donald C [last name deleted for privacy by Editor]
- Brooklyn, New York


A. Hi, Donald. I don't think you did anything wrong.

Nickels probably will not corrode in either fresh water or salt water in a reasonable time. I'm not quite sure what lesson they are trying to teach you in your science class with this experiment, but the first principle in science projects is "the scientific method" -- you do a controlled experiment and try to honestly record the results (which apparently was that nickels won't visibly corrode in 5 days in either salt water or fresh water. You did good.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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January 3, 2008

Q. I am doing a Science experiment . My problem is does saltwater have an effect on coins. I will have 5 cups. 4 will be filled with saltwater and the last will be filled with freshwater. In one cup I will put 5 pennies, in another cup I will put 5 nickels, in another cup I will put 5 dimes, and in another one I will put 5 quarters. In the cup with freshwater I will put 5 pennies. I want to know when I should start the experiment and how long it would take for the coins to start rusting.

Alaa E [last name deleted for privacy by Editor]
- Metairie, Louisiana

January 4, 2008

A. Alaa, you've told us what you will do, and the next step is to do it. You don't need to know the expected results; actually, it's much better if you don't because you won't be tempted to fudge things ("junk science"). Run the experiment for as many days as practical, keeping notes about your observations at least once a day, then give us your results and we'll be happy to comment.

Actually, none of the coins will "rust", because rust is iron oxide, the corrosion product of iron and steel, and none of your coins are iron or steel. Hopefully some of the coins will start to corrode though; I'm betting on the pennies. Good luck!

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

April 15, 2008

Q. I only have 2 weeks. I need to find out if salt water will rust a dime faster then fresh water. If I can't do this in 2 with results I will have to do something new or fail. I need help

Gabrielle R [last name deleted for privacy by Editor]
- Battle Creek, Michigan, USA

April 15, 2008

A. Hi, Gabrielle. Please see our FAQ on Cleaning Pennies. Most of it is completely applicable to your project on "rusting dimes". Dimes can't rust (they're not iron or steel), but they can corrode or at least tarnish, but they probably won't very much in 2 weeks. Pennies are a better bet.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 29, 2008

Q. I'm in 7th grade, and I am doing a science fair project, and my question is Does coins rust faster in salt water, or fresh water?

Aleah H. [last name deleted for privacy by Editor]
- Lancaster,Virginia, United states

October 1, 2008

A. Hello, Aleah. Very few coins are steel or iron (1943 steel pennies are the only American coin that I've ever heard of that is steel), and only steel and iron can rust, because rust is the corrosion product of iron :-)

So the coins are not going to "rust". Almost as bad, I don't think any coins but pennies will measurably corrode in a reasonable period of time. But give it a try, and best of luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

November 4, 2013

Q. Hi I am in the 7th grade and need some help with my science fair project. I am doing the corrosion effect of salt water on copper pennies and was wondering if you could help me.
Thank you

Noah [last name deleted for privacy by Editor]
- Elk Park, North Carolina, North America

November 6, 2013

A. Hi Noah. I'd say get 6 pennies, all 1983 or later (because these will be zinc pennies clad with copper, whereas earlier pennies are solid copper). Try to find six that have relatively the same shine. Put one each in six non-metallic cups or bowls. Add a few measured ounces of tap water to all 6 bowls. Add a measured amount of salt to 3 of the bowls. Stir all 6 so the stirring or lack of stirring isn't a variable. Look at the pennies each day and see if anything is happening. Take pictures if convenient. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

December 28, 2017

Q. Hello my 3rd grader is doing a project on will iron rust faster in salt water than fresh water. We have done the question, hypothesis, variables, materials, procedures, now it's time for data collection don't know what the data collection needs to be. Please help

Tamara Mccallum
- Owings mills

December 2017

A. Hi Tamara. The project is about whether iron will rust faster in salt water than fresh water, so data collection means collecting any evidence that it does or doesn't. This would mean notes and possibly pictures of anything s/he observes having to do with the amount of rusting; maybe any paper towels or coffee filters which were used to wipe away rust, or filter rusty water, etc. In third grade s/he may not have weighed the iron before and after, but if s/he did, then the weights. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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