Science Buddies: "Ask an Expert"

For my project I put chicken bones, seashells and eggs in coke, diet coke, mug rootbeer and distilled water. I used these because they containe a lot of calcium and I thought the acid in the sodas would cause the objects to loose mass. I checked the pH everyday and weighed the bones, seashell and eggs. From my research I thought that the calcium based objects in the coke would loose the most mass after 10 days. I found that the when I averaged the mass lost for each solution, diet coke caused the greatest loss in mass. Coke caused the fastest change in pH. This is not what my research said would happen. Does anyone know why the coke did not cause more loss of mass than the diet coke? Thanks!

Hello adejong,

I don't know the exact recipe for the various types of Coca Cola. I know the recipe has changed over the years, varies from one bottling location to another, and also varies from one type to another--especially from "Classic" Coke to Diet Coke.

Why did you think that the sugar-based Coke would dissolve Ca fastest? Maybe the Diet Coke has slightly more acid in it or a different type of acid.

WW

My research indicated that Coke was more acidic than either diet coke or mug rootbeer and would therfore dissolve the calcium. I tested the pH of each liquid before I placed the calcum rich subjects in them and that is what I found. Coke was the most acidic followed by diet coke, mug rootbeer and my control distirlled water. I thought the higher acidity would dissolve more calcium causing a greater change in mass. My research implied that is the result I should expect. However, that is not what happened. Diet coke caused the greatest change in mass. I was not looking at the sugar just the acidity. Do you think the sugar would affect the rate of calcium absorbtion? I did not find any reseach to indicate that. Thank you for responding to my previous post.

Have you researched the chemical composition of your calcium sources? The chemical composition may significantly affect which beverage is more reactive with it.

The physical nature of a reaction that disolves a solid isn't likely to come to equalibrium for a very long time. The reaction rates for the various beverages may be significantly different and you may not have waited long enough for an accurate end result.

Some of the beverages that you are using are carbonated so there is also a gas equalibrium reaction going on as well.
Did you research or test how much carbonation was present in your initial beverages? In order for CO2 to be released, there usually are some +ions freed over time which would decrease the pH of the solution and/or participate in another chemical reaction.

Various components of the beverage may (probably) act as buffers which will affect your pH readings and the reaction rates.

Thanks so much!! I didn't think of the carbonation. I observed that when I dropped the seashells into the regular Coke it started to bubble a lot. I will see what I can find!! THANKS!!!!