Solidification of CaCO3 and CaHPO4

[moshe zaguri]

Hey all,

I Have a powder of CaCO3 which I want to solidify (Hope that the right term)
I don't expect it to be like a lime stone but rather like a cracker that I can hold.

So I tried mixing it with H2O (distilled) and oven-dry it (60c 24h) and I do get a cracker,
The thing is I'm not sure whether it's still only CaCO3 or maybe some reaction have changed it (or part of it).
I followed the previous discussion in PF of CaCO3 reaction with water (https://www.physicsforums.com/threads/reactions-of-calcium-carbonate.420445/) but I can't get what happen when you dry the whole thing and take the water out (does the HCO3 condense back to CO3 and connects with the calcium?)

Further more - I want to do the same with but add also CaHPO4 (1/20 the amount of CaCO3).
So if I'll mix them, add water and then dry it, will I get the same materials or any reaction is expected to happen?

Thanks a lot
Moshe

 

[Hillbillychemist]

Not sure what you are trying to accomplish here, if you just want some solid calcium carbonate (a chunk) just get a piece of chalk. When you mixed your calcium carbonate powder a tiny amount of it dissolved. When you then dried it in the oven you evaporated the water and the dissolved calcium carbonate acted as a glue binding the powder particles together as your cracker. You added nothing but water and removed nothing but water so you still have the calcium carbonate you began with.
The calcium hydrogen phosphate also has a very low solubility (0.0316g/100cc cold water) so will react similarly. Since both are calcium compounds there will be no reactions between them and you will simply have chalk with some calcium hydrogen phosphate added.

 

[DrStupid]

I followed the previous discussion in PF of CaCO3 reaction with water (https://www.physicsforums.com/threads/reactions-of-calcium-carbonate.420445/) but I can't get what happen when you dry the whole thing and take the water out (does the HCO3 condense back to CO3 and connects with the calcium?)

Yes, if the water you used contained CO₂ than CaCO₃ can have been dissolved as HCO₃^- and yes, by heating it turns back into CaCO₃. That's the main source of limescale.