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For an experiment we're trying to measure the amount of gas produced in this reaction. But we always find less gas then expected, then a colleague told me that it could be because some of the CO2 produced might get dissolved in the water/HCl solution. This reactions takes place at 310K. The reaction takes place under normal pressure in closed containers, when the pressure in the container reaches over 100mbar the container will release ~50mbar of pressure.

We add 0.2 grams of CaCO3 to 100ml of 0.1M HCl. The 0.1M HCl is dissolved in pure water. This should generated 0.002M of CO2, and if I did my calculations right that should be about 51.02ml of gas. But everytime we measure we get around 30% less. Is the difference there because of the CO2 that has dissolved in the water or is there anything wrong with my calculations? Tips and advice are welcome.

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    $\begingroup$ You have not shown any calculations yet... It should not be a problem to involve easily found solubility of CO2, which is 1.45 g/L at 25 °C (77 °F), 100 kPa. $\endgroup$
    – Poutnik
    Commented Aug 14, 2023 at 14:34
  • $\begingroup$ I have found that solubility, but I couldn't figure out how to calculate the solubility for 37C and pressure between 50 and 100 mbar. I found something about Henry's Law, but I couldn't get my head around it. I'll try to formulate my problem better next time. Chemistry is not my subject of expertise. $\endgroup$
    – Thomas
    Commented Aug 16, 2023 at 12:32
  • $\begingroup$ I assume there can be found data of solubility at different temperatures see this. Even if not, you can see significant portion of CO2 would dissolve. // Exact portion cannot be calculated, as due reaction dynamic, solution can be locally saturated, forming bubbles, while rest is yet not saturated. // Gas solubility is proportional to pressure. $\endgroup$
    – Poutnik
    Commented Aug 16, 2023 at 12:46
  • $\begingroup$ Thank you, that is a useful table. I think the best I can do is try to saturate the water before the reaction to make sure it's as accurate as possible in gas production. Thank you for your help. $\endgroup$
    – Thomas
    Commented Aug 16, 2023 at 13:01

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Certainly $\ce{CO2}$ dissolves in water, and the experiment design allows an over-pressure of 50 mbar, so cannot go to completion, since $\ce{CO2}$ is still present. You've made club soda, or seltzer, if you prefer. Considering the temperature and dissolved solids, this might be a fair model of $\ce{CO2}$ in mammalian body fluids, e.g., ~25 millimoles per liter (mmol/L) in human blood. Ah! Read Michael Crichton's Andromeda Strain.

To find how much is dissolved in the solution, look at tables such as this. Note that the bicarbonate ion is important: "Calcium carbonate reacts with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate. $\ce{CaCO3 + CO2 + H2O -> Ca(HCO3)2}$. $\ce{CO2}$ solubility is influenced by the carbonate-bicarbonate buffer system.

However, check molar quantities of reactants and see if one limits the reaction!

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  • $\begingroup$ There is 10 mmol HCl and 2 mmol CaCO3, 6 mmol HCl, resp 0.06 M HCl would left. Not much of HCO3- there. $\endgroup$
    – Poutnik
    Commented Aug 14, 2023 at 15:12
  • $\begingroup$ Thanks for the sources, I wil look those up. The experiment is designed to have an abudance of HCl so that most/all CaCO3 will react. As I'm not a chemist but a Biotechnician, can I ask if the Calcium Bicarbonate will also eventually react and produce CO2, or are those innert? $\endgroup$
    – Thomas
    Commented Aug 16, 2023 at 12:40
  • $\begingroup$ Unless one or more of the products are removed, e.g., CO2 going into air, or a solid precipitating out, reactions can proceed in both directions, eventually reaching equilibrium where the amount of reactants going equals the amount of product reverting to the reactants. So, yes, the bicarbonate only exists in solution, in equilibrium with carbonate, bicarbonate and dissolved CO2. See en.wikipedia.org/wiki/Calcium_bicarbonate That 50 mbar CO2 pressure prevents it's complete loss. This seems like a good but simple model of body CO2 chemistry! $\endgroup$
    – DrMoishe Pippik
    Commented Aug 16, 2023 at 13:54

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