Do soft drinks corrode metal?

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A. I saw this experiment on TV. Here's how you do it: You place a corrosive metal such as iron, steel, or zinc into the liquid. Then place a non corrosive metal such as copper or graphite into the liquid with it. Very important: MAKE SURE THE METALS ARE NOT TOUCHING! That would ruin the experiment. After a couple of days or weeks (longer the better) the corrosive metal should be smaller or have holes in it. This experiment works best if you are using acids like citric (citrus juice) or acetic (vinegar). The soda might not work as well but give it your best shot. I've done this experiment with ascorbic acid and it worked great. Good Luck!

Paul C. Gianni
- Redding, California

Q. I am gonna perform an experiment about steel corrosion and how it is affected by different types of liquid. I was thinking of using water, salt water and a soft drink. Do you think I made the right choice of liquids?

January 29, 2012

A. Hi, Kai. Teachers and school books apparently often suggest soft drinks. I think there are two main reasons that they do so: 1) because soft drinks are safe and non toxic (especially important for younger kids); 2) to try to show children that soft drinks are bad for them (don't fall into a junk-science trap though).

Personally, I think soft drinks are not a very good choice:

1) They are carbonated; upon opening the bottle, the carbonation rapidly fizzes away, so the effect upon steel may be rapidly varying. Is the corrosivity primarily due to the fully carbonated, or fully de-carbonated liquid, or is there a critical carbonation level where most of the corrosion took place? Or is the effect of the carbonation irrelevant? Who knows, but maybe you could shake heck out of the soda before exposing the steel to it?  :-)

2) All soft drinks are proprietary, i.e., the ingredient list is secret and changeable. How can we learn much science if we don't know what is in them that may be causing the corrosion, and if they are free to change the ingredient list tomorrow? I think vinegar and fresh squeezed fruit juices are better choices for very young children, and that real chemicals (carefully identified acids and bases of labeled normality) are required for high school chemistry. Best of luck!

Regards,

Ted Mooney, P.E. finishing.com Brick, New Jersey

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