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Do coins rust faster in salt water or fresh water

(2007)

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


(2007)

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. RET
finishing.com
Pine Beach, New Jersey

January 3, 2008

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

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

April 15, 2008

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

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.

Regards,

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

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September 29, 2008

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

Hi, 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.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
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 varible. Look at the pennies each day and see if anything is happening. Take pictures if convenient. Good luck.

Regards,

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