Letter 11013

Do coins corrode more in salt or fresh water?

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I need to know if coins corrode more in salt or in fresh water.

Is an emergency. I appreciate if you could answer me as fast as you can.

Thank you.

Andrea V [name deleted for privacy]
- Miami, Florida, USA

An emergency, Andrea? Is someone choking on a coin and you want to know which kind of water to pour down their throat to dissolve the coin?   :-)

Seriously, this is a public forum and a good reply may not come until next month, or after you graduate. Sorry! But explain your science project or patiently apply the search engine -- the question is answered many time on this site. Good luck!

Ted Mooney, P.E.  finishing.com Brick, NJ

How can I find research on coins rust faster in salt water or fresh water? For my daughter's project she's in 6th grade.

Thanks,

Tina S [name deleted for privacy]
- Jacksonville, Florida

Check the town library (maybe the reference section) for a book on "Corrosion", Tina; the issue of salt water vs. fresh water corrosion will be covered, although maybe at a level beyond her grade. The librarian can help with age-appropriate stuff.

Salt water conducts electricity because it has salt ions dissolved in it that can transport electrical charge. This means that larger galvanic corrosion currents can flow. If a coin is made of two metals, like post-1982 pennies (which are copper plated zinc), the chemical reactions between copper and zinc will go faster.

Also chlorides (salt is sodium chloride) are corrosive. You've probably heard that cars corrode faster in the industrial belt where salt is applied to icy roads. Good luck!

Ted Mooney, P.E. 
finishing.com
Brick, NJ

My mom and I have been working on a corrosion project. we have the cups set up with salt and coins in them and we have been documenting them for the past 2 weeks. And now the teacher is asking for wbesites on where we are getting my information.. funny thing is I have been doing this experiment with no computer. And now that I need websites that have more information on this we can not find them. I was hoping someone out there would have an insite on some websites that we could look at?? Thanks for anyones help in guiding us to more knowledge.

CHARLES [name deleted for privacy]
6TH GRADER - WPB FL

There are dozens of threads on the subject on this site, Charles. We hope they'll help. But what were your results? What "hypothesis" did they support or tend to disprove?. Because the real purpose of this exercise is not to prove that salt water corrodes a coin faster or not, but to get you to practice the methods of conducting an experiment.

Now here's the thing. If your results were like mine -- that is, that the salt water did not corrode the coin faster -- yet your research says that salt water is more corrosive, what is your project going to say? Being in sixth grade I don't think you are prepared to explain the science behind that conflict; rather, I think you will say that it is widely reported that salt water is more corrosive than fresh water but your experiment did not demonstrate it. That is an interesting result because you can justifiably say "prove it! -- my results don't support that claim". Good luck!

Ted Mooney, P.E. 
finishing.com
Brick, NJ

Mr. Me and a couple of friends are doing a 9th grade science project and we want to know, were to get information on this question "Do coins rust faster in saltwater or freshwater?" we need as much help as possible this is counted for 5 grades and we need help!

Desera M [name deleted for privacy]
Student - Dallas Tx United States

Here are the two different approaches you could take, Desera:

1. Do the research first or
2. Do the experiment first

The first leads to "junk science" (deciding what you want the result to be, then doing the experiment again and again, as wacky as necessary until it finally comes out the way you were led to expect. Then you cross your fingers and hope it would come out the same way next time.)

The second approach leads to 'the scientific method', i.e., "This is found we found and proved (at least for our limited circumstance). Now, let's see how the science explains our results or warns us to avoid misinterpreting our results and jumping to the wrong conclusion". So tell us the results you got and we'll try to help you explain them. Good luck.

Ted Mooney, P.E. 
finishing.com
Brick, NJ

I am conducting an expirement concerning the rate of corrosion versus the amount of salt in water. I did my research and concluded that metal should rust faster in relation to the salt content of the water. However, the opposite is true. I have several jars set up. the first being pure distilled water, then a series with 2 tsp, 4 tsp, and 8 tsp of salt in 4 oz of water. While trying to answer why my experiment came out opposite of what I thought, I found several confusing answers all written for more advanced students. Can someone offer an easy to understand reason. I am going to give my experiment two more days, then repeat it to see if it comes out the same.

Thanks,
Courtney
5th grade

Courtney J [name deleted for privacy]
- Fort Bliss, Texas

Your results are your results, Courtney; if they do not support the theory that more salt leads to faster rusting, that's fine.

Science is based on experiment, not consensus! If you read that "The majority of scientists believe . . .", what that really means is everyone is still just guessing.

But I think that once you have 2 tsp of salt in 4 ounces of water, it's plenty salty. I would not expect more salt to have any effect. In fact, when you see any salt "sludge" in the bottom of your bowl, you've passed the "solubility limit" and any extra salt isn't dissolving anyway.

If you were in high school and the laboratory had an analytical balance (a very precise scale), you might be able to weigh the metal after immersion to determine which piece had the greatest weight loss, but just going by eye on the amount of rusting, my results were the same as yours. It is true that salt water is more corrosive than fresh water, but the experiment apparently needs to be conducted differently to prove it, and I don't know how a 5th-grader can prove it. I'd suggest that when the test is done you rub all the rust off the metal onto the inside of a coffee filter, then pour the remaining water through the coffee filter and display these rusty coffee filters as your evidence of which solution caused the most rusting. Good luck.

Ted Mooney, P.E. 
finishing.com
Brick, NJ

I'm doing a science experiment for 6th grade and I'm trying to figure out the corrosive effects of fresh versus salt water over time on various steel surfaces, from untreated, to brass plated, zinc plated, painted, etc, to see what happens to such common building materials with exposure to elements over time.

So far, my results completely contradict the information I've read in books. My materials are completely under either fresh or salt water kept at a constant temperature. I didn't use a cover. They are exposed to air, like regular building materials would be. They seem to be corroding at the same rate yet I know that's not possible.

Can someone please give me some advice on what I'm doing wrong?

Francesca L [name deleted for privacy]
Student - New York, NY

Please help me find which coin will corrode faster in fresh or salt water!!!please today!!!!!!!! I have no sotuation.

Jazmine S [name deleted for privacy]
student - Houston, Texas, USA

I am in 6th grade with a science fair that counts for much of my grade. I am required to have 2 research sources (1 print based)and am wondering how to get them. My project is about corroding coins in freshwater, salt water, and chlorinated water. This is the only site I could find that really helps me. Please post your response soon. Thanks!

Ray B.
6th Grade Student - Boone, NC, USA

I want to post a question or inquiry of my own.

 

I want to answer or follow-up on this question publicly (in non-commercial fashion).