May 24, 2024, 04:04:02 PM
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Topic: Burnt boiled egg in water = shiny, mirror-like appearance. Why does this happen?  (Read 5514 times)

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Offline violin_chic_05

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My mom showed me this mini chemistry experiment I could use in my classroom, but I don't quite know what the chemistry is behind it. I want to be able to explain it to my students.

You carefully burn a boiled egg, over a candle or another open flame (not sure if a Bunsen burner would be too hot, I haven't tried it yet - could just make the egg crack because of the heat). I just use some regular BBQ tongs to hold it over the flame to avoid getting burned. You also want to wave the egg around, not hold it right over the flame for too long, otherwise it will crack. Naturally, it turns black. You want it completely black, not just lightly burnt. It works the best if the WHOLE egg is black (you may need to rearrange how you're holding the egg to get all parts).

You carefully place it in a glass full of water (a jar of some kind would work the best - something with a wide mouth so you can easily place the egg in. Don't drop the egg - all of the carbon around the egg will come flaking off). The egg ends up looking like a mirror, with a very shiny coating. When you remove the egg, it is still dry (where the carbon hasn't flaked off).

I know that carbon is non-polar, and water is polar, so that's why there is a sort of protective covering of air around the egg in the water, and why it's dry when you pull it out of the water. My question is, why a boiled egg? Would this work with anything else that was burnt? I don't think I've seen this effect with anything else that has been burnt and placed in water. Is there something about the proteins in the egg shell that cause this effect? Would this work with a raw egg?

Offline violin_chic_05

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It does work with a regular egg. Just tried it. Guess it's just easier to deal with messes caused by a boiled egg. And if you let your students try this, there's bound to be someone who drops their egg.

Offline vmelkon

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The egg gets coated with amorpheus carbon, a non crystalline form of carbon. The surface of that carbon is very rough.
When you dip it in water, the water is unable to displace the thin amount of air that is on the surface.
So, once the egg is in, the at the air-water boundary, you get total internal reflection if your viewing angle is right.

All that is in the domain of physics : the physical properties of amorpheus carbon. The physical properties of water. The properties of light (reflection and total internal reflection).

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My question is, why a boiled egg?
Because of its curvature. Try it with a flat object.

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Is there something about the proteins in the egg
No.

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