fusso
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Chalk composition: CaCO3 vs CaSO4
https://www.youtube.com/watch?v=iksYmkSTzmQ
From TKOR's vid their bought chalk don't dissolve in HCl. They also provided a DIY recipe using CaSO4. What's the difference between CaCO3 and CaSO4
chalk?
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RedDwarf
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If you're talking geologically or chemically then chalk is calcium carbonate, but the word chalk is often used to describe other (compressed) powders
such as blackboard/sidewalk chalk, billiard chalk or climbing chalk (normally but not always magnesium carbonate) which can be of different
compositions. Context, as ever in language, is everything!
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fusso
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I'm talking about writing/blackboard chalk.
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PirateDocBrown
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Blackboard chalk is almost always gypsum, CaSO4.2H2O.
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
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zed
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As I recall, gymnasts may utilize CaCO3 chalk.
I'll check!
Well, I checked, and I stand corrected. Seems Gymnast's chalk may be MgCO3.
Plenty of other sources of CaCO3. At least, if you are in the USA.
[Edited on 2-10-2019 by zed]
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hodges
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Years ago, I remember reacting chalk board chalk with an acid and getting CO2. So the chalk I had was definitely a carbonate. I don't know what
chalk board chalk is made of these days. I didn't even realize it was still made given most boards being white boards these days. I guess a few
vendors still have chalk boards with ads on them on sidewalks outside their shops.
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Sigmatropic
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Lime, as in lime stone is also calcium carbonate. Giving quicklime on calcination, in turn giving slaked lime on hydration. Also calcium chloride is
available as a desiccant. At least one of these is bound to be in your local hardware store.
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