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Topic: Making a calcium carbonate saturated solution  (Read 656 times)

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Offline rwooduk1

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Making a calcium carbonate saturated solution
« on: November 03, 2019, 02:27:38 PM »
Hello,

I came from another well knowN forum to this forum to get some more chemistry help on my experiment. Basically, I want to make a saturated calcium carbonate solution, then use an electrochemical method to form calcium carbonate deposits on a surface. I understand the electrochemical method now, but am unsure how to make the initial calcium carbonate solution.

Most of the papers simply say to put CaCO3(s) into deionised water then bubbling CO2 into the solution causing it to dissolve. Then, when the CaCO3 is fully dissolved (no visible particles) to keep the solution "at rest" until excess CO2 is released and pH reaches a value of close to 7. At this pH supersaturation is too weak to cause spontaneous nucleation of CaCO3. So then I will have my saturated CaCO3 solution.

I understand the process, but I am unsure of how much CaCO3 will dissolve in my volume of water, how much CO2 will I need? Is there some sort of calculation I can make? For my experiments I will have to have the same saturation level of CaCO3 in each test solution, how will I ensure that they are the same?

Lastly, when electrochemical deposition happens the oxygen in solution is reduced forming hydroxyl radicals, increasing the pH and causes scale deposit on the working electrode. Would a diffusing O2 into solution increase the deposition rate?


Offline AWK

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Re: Making a calcium carbonate saturated solution
« Reply #1 on: November 03, 2019, 03:15:52 PM »
Check calcium bicarbonate in Wikipedia
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Offline rwooduk1

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Re: Making a calcium carbonate saturated solution
« Reply #2 on: November 04, 2019, 05:47:48 AM »
Hi, thank you for your help. The Wiki page doesn't give information on the amounts. I have been looking at The Langelier Saturation Index as a method for potential measurement, where LSO < 0 would indicate no potential to scale and LSI > 0 indicates there would be precipitation. It uses a method of pH measurement. Is anyone familiar with this method, or other methods I could use, such as the supersaturation index (SI)?

I guess a visual inspection of the solution when saturation is complete (i.e. large particles present in solution) may be adequate, but just trying to see if there is anything more precise.


Offline AWK

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Re: Making a calcium carbonate saturated solution
« Reply #3 on: November 04, 2019, 05:50:32 AM »
Wiki gives solubilities of calcium hydrogen carbonate. That's enough for a chemist.
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Offline rwooduk1

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Re: Making a calcium carbonate saturated solution
« Reply #4 on: November 04, 2019, 07:19:24 AM »
I see, okay thank you again for your help.

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