shae05
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*URGENT* Acetic Acid Affect on Shells

Postby shae05 » Wed Mar 27, 2019 3:36 pm

I have done the Swimming in Acid/Ocean Acidification project and gotten some pretty good results, AND I am advancing in my science competition. However, it would really, really help my presentation if I knew why you guys used acetic acid to lower the pH of the saltwater and not something else. I need this pretty quick. Thank you!!

SciB
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Re: *URGENT* Acetic Acid Affect on Shells

Postby SciB » Sat Mar 30, 2019 5:41 pm

The only reason I know of is that everyone has access to acetic acid in the form of vinegar, which makes it much more convenient to do the experiment.

In seawater, the acid is carbonic which forms from dissolved carbon dioxide from the air. As CO2 levels rise from burning fossil fuels and other sources, more dissolves in the oceans which lowers the pH and can adversely affect creatures that have shells.

So, ideally, the way you should do this experiment is to use carbonic acid and shells of some marine creature. This is not practical for a high school science fair, so that's why we substitute eggshells for mollusk shells and vinegar for carbonic acid. It is really a demonstration and not an actual experiment. The dissolving of eggshells in vinegar is not equivalent to changes in marine shells in seawater.

If you have more questions, please post again.

Sybee

SciB
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Joined: Fri Feb 01, 2013 7:00 am
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Re: *URGENT* Acetic Acid Affect on Shells

Postby SciB » Sat Mar 30, 2019 6:12 pm

My mistake. I should have checked the project description. I see that you used mussel shells which ARE a marine organism, so the demonstration is closer to reality. But it is still not necessarily true that acetic acid (did you use distilled white vinegar?) would have the same effect as carbonic acid. Mussel shells are formed from calcium carbonate and dissolving more CO2 in the ocean can reduce the amount of carbonate which acetic acid would not be able to do. The pH of the vinegar-acidified seawater, 7.5, will be equivalent to that of the projected pH of seawater in the year 2100 if CO2 levels continue to increase at current levels.

The experiment could have been repeated using hydrochloric acid instead of vinegar to make acidified seawater at pH 7.5 and that would have made the results more convincing if both acids gave the same results. Then you could conclude that it was the pH that was responsible for the effect and not the type of chemical acid used.

I hope this explanation helps. If you have more questions, let me know.

Sybee


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