MadSci Network: Chemistry

Re: Why does Coke remove rust better than Sprite?

Date: Fri Apr 14 07:35:35 2000
Posted By: Chris Cerrato, Staff, Compounding Dept., C. L. Hauthaway & Sons
Area of science: Chemistry
ID: 955339151.Ch

     To a certain extent, any carbonated beverage will remove rust. This 
is because the gas used, carbon dioxide, when mixed with water, makes 
carbonic acid. To make rust, the iron oxidizes, which is why rust is also 
called iron oxide. What the carbonic acid does is drive the reaction the 
other way, which is called "reduction." If you read the ingredients of 
both Coke and Sprite, now that you know it's an acid doing the work, you 
can see why Coke works better - it also has phosphoric acid as an 
ingredient. Phosphoric acid is what does most of the work in Naval Jelly, 
a commercial product used for rust removal.
     This is also why the rust that isn't dissolved off turns black. It's 
because it's turning back into metallic iron.

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