Why Molasses Gets Rid of Rust
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Question
I have a friend who uses molasses to clean rust off old iron items collected from the bush. The rusty iron article is placed in a jar of molasses solution (nine parts water, one part molasses) and left for two weeks. After this time, the article comes out clean and almost shiny. What is happening here?
Answer
Molasses contains chelating agents. These are made of molecules that are shaped a bit like the claws of a crab--the word chelating comes directly from the Latin word chele, meaning claw. They can envelop metal atoms on the surface of an object, trapping them and removing them. Molasses owes its properties to cyclic hydroxamic acids which are powerful chelators of iron.
More of these compounds are found if the molasses is derived from sugar beet rather than cane sugar. The plants from which molasses is made presumably use these chelating agents to help them extract minerals from the soil. Interestingly, there are aerobic microorganisms that use similar cyclic hydroxamic acids to scavenge iron. So plants and microbes appear to use the same chelation strategy to obtain their daily ration of iron.
The same process is at work when you clean old coins with Vegemite or cola. The power of chelating agents also explains why the insides of tomato tins need to be lacquered. The citric acid in the tomatoes would dissolve the metal of the container if the lacquer were not present. Household cleaning agents, especially detergents and shampoos, also rely on chelation. These soften water to make it more effective during the cleaning process.
Chelation has its uses in medicine, too. EDTA or ethylenediamine tetraacetic acid is used as a chelating agent to control levels of calcium in the body and can reduce the effects of mercury or lead poisoning.
Ben Selinger, Department of Chemistry, Australian National University. Ben Selinger is the author of Chemistry in the Marketplace and Why the Watermelon will not Ripen in your Armpit (Allen & Unwin)
petrol tank dipped in molasses as described earlier in post #9. Prior to treatment the whole tank was as bad as the rusty part, which remained rusty because my molasses tank was not deep enough to submerge the whole petrol tank. Looking at this picture, why would anyone not use molasses?
