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Topic: Ca2+ ion concentration when dissolving CaCO3 in lactic acid  (Read 3132 times)

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Offline phuayijing

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Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« on: March 05, 2015, 03:12:07 AM »
I would like to know how much Ca2+ ions will be produced in a solution containing CaCO3 and lactic acid at equilibrium.

Lets say I am dissolving 1g of CaCO3 in 1ml lactic acid (200mM), how much Ca2+ ions are there in the solution at equilibrium state? How if I increase the acid volume to 2ml? (given that other parameters such as acid molarity, temperature, pressure are in constant).

I spent a lot of time in literature review but I still haven't managed to figure out how should I calculate it. Hopefully someone here can help me. Thank you. ^^

Offline Borek

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Re: Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« Reply #1 on: March 05, 2015, 03:44:57 AM »
You will need constants for all equilibria present in the solution. Can you try to list them? (IOW: start by listing all reactions taking place).
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Offline phuayijing

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Re: Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« Reply #2 on: March 05, 2015, 04:28:10 AM »
You will need constants for all equilibria present in the solution. Can you try to list them? (IOW: start by listing all reactions taking place).

Thank you for your reply. These are the details that you requested:

CaCO3 (s)  ::equil:: Ca2+ +CO3 2-       Ksp = 5.0x10-9

CH3CH(OH)CO2H    ::equil::  H+  +  CH3CH(OH)CO2-    Ka=1.38 × 10-4

Hydrolysis of carbonate ions occurred during the dissolution:
HCO3-  ::equil:: H+ + CO32-       K=4.8x10-11

Offline Borek

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Re: Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« Reply #3 on: March 05, 2015, 05:37:41 AM »
That's not all yet - carbonic acid is diprotic. Also I guess lactic acid is a complexing agent, so there is an equilibrium between calcium and lactate present in the solution. Not to mention water autodissociation.

Do you know what are mass and charge balance equations? You will need them as well.
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Offline phuayijing

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Re: Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« Reply #4 on: March 05, 2015, 07:05:21 AM »
That's not all yet - carbonic acid is diprotic. Also I guess lactic acid is a complexing agent, so there is an equilibrium between calcium and lactate present in the solution. Not to mention water autodissociation.

Do you know what are mass and charge balance equations? You will need them as well.

Wow... sounds so complicated.  :( I am sorry that I do not have chemistry background (I am working on material engineering), but the research I am carrying out now requires the understanding of the CaCO3 dissolution. I will try to google the mass and charge balance equations, hopefully I can find any.

Thanks again ^^

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Re: Ca2+ ion concentration when dissolving CaCO3 in lactic acid
« Reply #5 on: March 05, 2015, 08:16:52 AM »
The principle is quite simple. Mass balance means that whatever was put into the system stays there (nothing else but a mass conservation), charge balance is a way of expressing the fact solution is electrically neutral (sum of all positive charges equals sum of all negative charges). These plus all equilibria describe the system - it typically means you have a system of n unknowns and n independent non-linear equations. Solving them manually is a nasty thing, it is better to use some kind of solver.
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