[Nihilist]

My plan is

Add marble chips to some HCl until they stop reacting and there is some left at the bottom of the beaker.

Filter and throw away the excess CaCO₃. The solution should be neutral by now

CaCO₃ + 2HCl --> CaCl₂ + CO₂ + H₂O

Boil the solution down until there is little enough to put into a flat dish and to dry it off in an oven.

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For my electrolysis setup I'm gonna use a 12v adjustable DC adaptor and carbon graphite rods from inside the big square batteries that are used in torches for the electrodes.

There will be about 4/5 cathodes depending on how many I can get and only 1 or 2 anodes. Im using more cathodes so I'm able to pick up more Ca at once.

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Melt the CaCO₃ CaCl₂ (takes near 800ºC) and place the electrodes into it then turn it on.

Do this outside or in a fume cupboard!! Cl₂ gas will be released, this is poisonous and if inhaled. As Cl₂ is heavier than air it will fall towards the ground.

Cathode equation:
Ca²⁺ + 2e -> Ca

Anode equation:
2Cl^- -> Cl² + 2e

Questions:

What would the erosion on the electrodes be like? Would there be a better choice for this experiment? (I wonder how much some platinum rods would cost...)

Are my equations right?

Suggestions and comments welcome


EDIT: Just fixing those sub things

[AWK]

1. To obtain anhydrous CaCl₂ you need at least 260 C.

2. Industrial electrolysis is conducted at 780-800 C in iron vessels with graphite electrodes.
At this temperature calcium chloride is molted (mp 772 C).Mixture with CaF₂ (mp=816 C) is used instead of pure calcium chloride.

3. CaCO3 start decomposing at this temperature (not melting). Electrochemistry is OK. Process should be done in stream of inert gas (eg argon). Chlorine is extremely toxic. You forgot about diffusion of gases.

My comment to questions. Platinum react with chlorine over 500 C and cannot be used as material for electrodes. Iron reacts with chlorine at 350 C giving FeCl₃ which easily sublimes but at 800 C thermodynamically stable is FeCl₂ which does not sublime and corrosion is not too dangerous for vessel.

[Nihilist]

Oops. I didnt mean to say melt the CaCO3   I meant the CaCl2.

Why is CaF₂ added to the CaCl₂?

What would happen if I used Iron nails for the cathodes? Would this affect the amount of Cl₂ gas produced?

[AWK]

CaF₂ is added as fluxing agent. It can also undergo electrolysis if to high oltage will be used.

Yes, iron electrodes after reaction with chlorine will greatly decrease current strenght.

[Donaldson Tan]

What's a fluxing agent? Something that lower the melting point of the molten electrolyte?

Isolation of Ca? They would form near the cathode? I think Ca would have a lower density than molten CaCl₂. If so, u can just tap it off