Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Schwarz107 on October 05, 2017, 10:05:30 AM
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I am showing some kids how vinegar can dissolve an egg shell, which begs the question if any acid (which loosely defined is just a liquid with a rather high concentration of H+ ions?) can dissolve an egg shell?
What is it about acids, or more specifically the H+ions, that makes them able to dissolve things?
Let's say you have a solution with a pH of 0, meaning many H+-ions – why would that cause such damage to i.e. skin?
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Yes any acid will dissolve egg shell. Check which material egg shells made from. Acids also harm human and animals, because the living material is made by proteins an and amino acids, which can be dissolved easily.
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I am showing some kids how vinegar can dissolve an egg shell, which begs the question if any acid (which loosely defined is just a liquid with a rather high concentration of H+ ions?) can dissolve an egg shell?
What is it about acids, or more specifically the H+ions, that makes them able to dissolve things?
Why not look up the reaction, and write it out. Its a good thing for the kids to be exposed to, learning the "Why?" beyond "Zomg. Watch this. Watch this. Watch this. This is so kool! Ke ke. ke"
Let's say you have a solution with a pH of 0, meaning many H+-ions – why would that cause such damage to i.e. skin?
Now that's a more complex problem. It will be harder to understand the chemical reactions involved. I that case, we sometimes defer to general rules for laboratory safety. You can look those up, too. Also a good lesson for kids. Sometimes, a child or even a grownup has to just accept rules.
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Thanks for the replies. I've bought a chemistry kit for children 12+, but I haven't had chemistry myself, so I'll have to teach myself before I teach the kids (two boys).
What I am curious about is really why solutions with many H+ ions can "destroy" so many things.
Say, you have a liquid with a pH of zero, and you put it in contact with any organic material, the result would be hazardous. How come?
@chenbeier. You mention that many H+ ions can harm humans because we are in part made by proteins and amino acids. But wouldn't a solution with many H+ ions also destroy teeth?
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Simply put, is the answer that H+ ions are lacking an electron, and therefore bond quickly, and as they bond quickly they are highly reactive?
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@chenbeier. You mention that many H+ ions can harm humans because we are in part made by proteins and amino acids. But wouldn't a solution with many H+ ions also destroy teeth?
Of course they do almost everybody has problem with caries.
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Simply put, is the answer that H+ ions are lacking an electron, and therefore bond quickly, and as they bond quickly they are highly reactive?
I am afraid you are trying to find an oversimplified answer to a much more complicated reality. It is a dangerous approach - easy to introduce misconceptions that are later difficult to fight.
Better put it as "H+ is highly reactive" without going into details.
Reaction with proteins is very different from the reaction with egg shells and metals, so while yes, acids do tend to destroy the skin, I would not put it into the same basket as CaCO3 reaction.
Perhaps you will better keep to separate facts for now, without trying to generalize.
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@Borek. I like the proverb that "A model is a lie that helps you see the truth", but of course, I don't want to create misleading and lasting models. What do you think about this simplification. Is it stretching it too far?
They are young boys, and I wonder about saying something like that: «When a hydrogen atom is stripped of its electron, it's like someone would strip them of their pants: They would do anything to get back their pants back, and so would the hydrogen atoms. So therefore H+ ions bond with many substances.»
I am a neophyte myself, so I try to learn as I go. Input and suggestions are much appreciated.
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The issue is that introduction of an acid can degrade a material different ways depending on the substrate and the acid choice. A carbonate salt is going to dissolve pretty much the same way in all acids due to direct protonation of the carbonate anion.
However an water insoluble protein is not going to dissolve very well in aqueous acetic acid. It will dissolve in hydrochloric acid because the bonds between individual peptide units are being cleaved, and each unit is pretty water soluble. If you instead use nitric acid, it is a powerful oxidizer in addition to being a strong acid, so it will cleave individual units as well as perform oxidizing reactions and tear the individual peptides apart even!
Does this help you see why we have so much trouble generalizing for you?
I do like your analogy, but it really only works for solubility swings that depend on protonation.
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If you hydrolyze a protein, you need to work at very high concentration of HCl, to heat to over 100 °C, and to wait about 24 hours. This will convert the protein to amino acids. Some amino acids (tryptophan, glutamine, and asparagine come to mind) are sensitive to acid, but others are not.
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«When a hydrogen atom is stripped of its electron, it's like someone would strip them of their pants: They would do anything to get back their pants back, and so would the hydrogen atoms. So therefore H+ ions bond with many substances.»
To build on that analogy: you have to remember pants are not the only solution. You can put on briefs, you can wrap yourself with a towel and so on. Many ways of hiding what you want to hide, many ways for H+ to react with different substances.
Plus - while H+ definitely is reactive, there are things that make it look pale, so don't leave your boys with a feeling they have just meet the reactivity king!