How to determine the amount of CO2 sodium hydroxide absorbs?

I first created a solution of $\ce{NaOH}$ and water, 5g of $\ce{NaOH}$, and 100ml of water, with a pH of around 14. I then added $\ce{CO2}$ (mixing baking soda, citric acid, and water) to the solution. The pH then dropped to 11 forming sodium carbonate.


I would like to know how much $\ce{CO2}$ was absorbed by the solution. Can I do this with the data I already have?




No, you cannot determine precisely with the data you collected (for example, a pH value 'around 14'). Some of the generated carbon dioxide gas also may have escaped or not reacted with the high pH solution.


Remember, pH is a log scale and lose of precision can be significant. However, you may argue, within the measurement error of the pH scale, you are approximately correct. Also, you are assuming correct calibration of the pH device. Mention the nature/degree of possible errors in your write-up.


Also, correct procedure matters, so if you did not add pure carbon dioxide gas directly, meaning you added the citric acid plus Baking Soda into the aqueous $\ce{NaOH}$, some neutralization by reactions with the sodium hydroxide by the citric acid and Baking Soda. The latter will skew the presumed amount of $\ce{CO2}$ actually released.


If appropriate, some added work. For example, test by adding dissolved calcium chloride, in excess, to the solution. Proceed to collect, dry and weigh the recovered calcium carbonate. Moles of the latter equate to moles of consumed carbon dioxide, albeit, expect some $\ce{CaCO3}$ collection loss.


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