Rebreather World - View Single Post - Chemistry and Physics in sealed part-used scrubbers

Abbo · 10th January 2008, 23:52

Quote: (Originally Posted by Molecular Products Ltd)

The reaction sequence shown in your note is an oversimplification of the actual chemical reaction sequence that occurs. Sodium carbonate is not formed at the pH of the reactions, it is sodium bicarbonate that acts as the carrier molecule. A better description is:

Overall: CO2 + Ca(OH)2 => Ca(CO3) + H2O made up of the individual stages:

CO2 + H2O <=> CO2 in solution (it just dissolves - it does not form carbonic acid)

CO2 + NaOH => NaHCO2

NaHCO3 + Ca(OH)2 => Ca(CO3)2 + NaOH + H2O

I'm not a chemist, but these equations appear to be wrong - not least because they don't balance. Correct me if I'm wrong, but shouldn't the equations be:

CO2 + NaOH => NaHCO3 (otherwise you have 3 oxygen on the left and only 2 on the right - plus you don't have a bicarbonate ion).
NaHCO3 + Ca(OH)2 => CaCO3 + NaOH + H2O
Otherwise the Cs and Os don't balance and you have the wrong formula for chalk.

10th January 2008, 23:52	#15 (permalink)
Abbo Nicholas Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 449	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) The reaction sequence shown in your note is an oversimplification of the actual chemical reaction sequence that occurs. Sodium carbonate is not formed at the pH of the reactions, it is sodium bicarbonate that acts as the carrier molecule. A better description is: Overall: CO2 + Ca(OH)2 => Ca(CO3) + H2O made up of the individual stages: CO2 + H2O <=> CO2 in solution (it just dissolves - it does not form carbonic acid) CO2 + NaOH => NaHCO2 NaHCO3 + Ca(OH)2 => Ca(CO3)2 + NaOH + H2O I'm not a chemist, but these equations appear to be wrong - not least because they don't balance. Correct me if I'm wrong, but shouldn't the equations be: CO2 + NaOH => NaHCO3 (otherwise you have 3 oxygen on the left and only 2 on the right - plus you don't have a bicarbonate ion). NaHCO3 + Ca(OH)2 => CaCO3 + NaOH + H2O Otherwise the Cs and Os don't balance and you have the wrong formula for chalk.
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