Chemical Forums

Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: rwooduk1 on November 03, 2019, 02:27:38 PM

Title: Making a calcium carbonate saturated solution
Post by: rwooduk1 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 CaCO_3(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?

Title: Re: Making a calcium carbonate saturated solution
Post by: AWK on November 03, 2019, 03:15:52 PM

Check calcium bicarbonate in Wikipedia

Title: Re: Making a calcium carbonate saturated solution
Post by: rwooduk1 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.

Title: Re: Making a calcium carbonate saturated solution
Post by: AWK on November 04, 2019, 05:50:32 AM

Wiki gives solubilities of calcium hydrogen carbonate. That's enough for a chemist.

Title: Re: Making a calcium carbonate saturated solution
Post by: rwooduk1 on November 04, 2019, 07:19:24 AM

I see, okay thank you again for your help.