All about the Carbonic Acid

The magical bumper cleaner, or nail dissolver, or tooth eater.  Did you ever wonder why Coke can clean the rust off a bumper (and not dissolve it) or dissolve a nail in a few days......why not just make the nail shinny like the bumper?

Not going to argue on the health issues of drinking Soda or Pop, as we called it where I grew up.  Anything other that raw vegetables, in excess can cause health issues.  For most of us we like a nice cold coke on a hot summer day, or maybe a glass of root beer with a scoop of ice cream.  It is all about moderation and to be honest no one will get me to stop enjoying a ice cold Pepsi or Coke every once in a while but here is the science as to why it is a myth

That fact you can cook and clean with Coke is relatively meaningless from a safety standpoint: you can use a wide array of common household substances (including water) for the same purposes; that fact alone doesn't necessarily make them dangerous to ingest.

Nearly all carbonated soft drinks contain carbonic acid, which is moderately useful for tasks such as removing stains and dissolving rust deposits (although plain soda water is much better for some of these purposes than Coca-Cola or other soft drinks, as it doesn't leave a sticky sugar residue behind). Carbonic acid is relatively weak, however, and people have been drinking carbonated water for many years with no detrimental effects.

The rest of the claims offered here are specious. Coca-Cola does contain small amounts of citric acid and phosphoric acid; however, all the insinuations about the dangers these acids might pose to people who drink Coca-Cola ignore a simple concept familiar to any first-year chemistry student: concentration. Coca-Cola contains less citric acid than does orange juice, and the concentration of phosphoric acid in Coke is far too small (a mere 11 to 13 grams per gallon of syrup, or about 0.20 to 0.30 per cent of the total formula) to dissolve a steak, a tooth, or a nail overnight. (Much of the item will dissolve eventually, but after a day or two you'll still have most of the tooth, a whole nail, and one very soggy T-bone.) By comparison, the gastric acid in your stomach's digestive fluids is much stronger than any of the acids found in Coca-Cola.

Excerpts from WebMD, Snopes, and my college chem class.