[JimeNutron]

Hello scientific community, I need help with a practical problem I've encountered while experimenting.

As an exercise in chemistry practices, I decided to use my spare time to recreate the calcium carbonate extraction from eggshell experiment I saw on Cody's Lab ( https://www.youtube.com/watch?v=1Ta1FuesnK0 ).

I bought distilled water from the supermarket as i have no way of distilling my own. I put the distilled water and cleaned (read: rinsed with soft tapwater) eggshell into a plastic bottle which i had rinsed with the distilled water. I then added dry ice and closed the lid after the dry ice was all consumed. After a day, the bottle had lost a noticeable amount of volume. I left the bottle for another 2 weeks but the volume did not change further. I then emptied the water in the bottle into a saucepan through a paper coffee filter. The saucepan had a spot of red/brown rust on the bottom but i had no better alternative. I boiled away the CO2 and water using my kitchen stove. As the CO2 bubbled out of solution, an off-white precipitate formed. However, there was also a very powerful odor, which could be described as rotten egg or "eggfart" as my father put it. The precipitate formed tends to clump together and sinks easily in the water, and is certainly not pure white; it has a yellowish tinge.

With a little bit of online research, i found a source that says that sometimes limestone can smell like rotten eggs due to hydrogen sulphide gas trapped in the stone. Hydrogen Sulphide gas has a very strong rotten-egg odor, while CaCO3 is supposedly odorless. Have I somehow formed sulphides or some other sulphur compound using just dry ice, water and eggshells?

I could really use some help identifying what contaminant/s is/are causing my CaCO3 sample to smell so bad. Are there any household chemicals I could use to test for different possible substances?

Thank you.

[Arkcon]

Hi there.  Welcome to the Chemical Forums.  Can you Google, check Wikipedia or check a textbook in the library for the composition of eggs and their shells for us, and report back what you've learned?

Sorry to answer a question with another question, but that's what we do here on the Chemical Forums.  We like to help you learn to help yourself, we're all better off if you try.  That's in our Forum Rules{click}.  You agreed to follow these rules when you signed up.

[JimeNutron]

Ah, sorry for posting in the wrong section of the forum. I forgot to mention that I am an undergraduate engineering student (so I posted this in undergrad chemistry because I thought "that's the level of chemistry I'm familiar with"), but the question doesn't have anything to do with my course so Citizen Chemist is probably the right place.

My understanding is that eggshells are about 95% CaCO3, with the other 5% being mainly magnesium, phosphates and proteins. I took a 1mL sample of the water that the off-white precipitate was suspended in, after the CO2 was evaporated out and added some NaOH to it to see if it reacted in any way. I didn't notice any reaction, so I guess the water isn't acidic?

As far as I can tell, I've recreated Cody's experiment to the letter; water + dry ice + eggshell, wait some time, filter the water, boiled off the water, collect precipitate. Is it possible that the rotten egg smell is caused by leftover organic material on the eggshells which rotted over the two weeks? Did I not clean the shells well enough? Or is the off colour and smell caused by Magnesium and/or phosphates? What did Cody do differently to get different results?

I'm not looking for the answers to these questions, just ways that i could answer them myself. Any hints on what sort of tests I could perform to determine the presence of different contaminants? I have tried to research this myself but I'm stuck because the only chemical associated with CaCO3 I can find that smells rotten is hydrogen sulphide, but I don't know where the sulphur could have come from. If the way I'm wording my query is against forum rules, then I could use some tips on how to use this forum more effectively.

[Borek]

Rotting leftover albumins, not much you can do about it. With some luck the sample is mostly sterile and rotting is not a problem, but there is no easy way to guarantee that. You can try to boil the eggshell in the distilled water before adding the dry ice (just remember to cool it down in a closed container, or at least in as closed container as possible - with as small opening as possible).

[JimeNutron]

Thanks Borek. I hadn't considered sterilising the shells beforehand, though that should have been fairly obvious in hindsight. I guess I didn't think of doing that because Cody didn't do it, and I was using his video as a guide. I'll have another go at the experiment soon with new eggshells.

[shiffdaddy]

Let us know how trial 2 goes