That formula seems wrong to me, in that the blank value should be subtracted from the sample value - a typo perhaps? As Steven Larson says, it will depend on the volume and molarity of the absorbing solution and the titrant. You can refer to Section 3.1 of the Rothamsted Lab Manual on my ResearchGate page for more information on this method (or one version of it anyway).

Dear Larson,

Thank you for your response. The HCl solution used for titration is 0.5 M, and the trap solution of KOH is also 0.5 M. In that case, what do the numbers of 1 and 6 mean or how should I continue to the calculation?

Thanks.

Dear Hart,

Thank you for make me re-check the formula. Again it does not seem false though. Since, the volume spent for blank samples is always higher than the amount spent for the samples. In the reverse situation, the result would be negative which does not make sense. Maybe this may give you a chance to re-check and correct the formulation given in your manual report.

Thanks.

First, some correction to the Steve post, CO2 is interacting with alkali, not with acid (agree?) and the molar ratio CO2:HCl should be NOT 1:1 but 2:1 if NaOH solution is concentrated. Second, the number '6' is probably related to the concentration of acid used for titration. Third, this archaic CO2-absorbtion technique could be subjected to systematic errors caused by kinetic factors (e.g. slow exchange rate at gas-liquid interface or leakage of jar seal), therefore my recommendation to Baris is to run simple calibration: inject known amount(s) of CO2 into your jar without soil, all other conditions being exactly the same. Then use simple proportion to find your CO2 amount evolved from soil.

Dear Mr Tercimen,

I am probably missing a lot of context, but your blanks will be just empty jars yes? In which case the CO2 absorbed by your KOH solution will be very small compared to the CO2 evolved from the soil samples. The HCl needed to titrate your blanks will also therefore be much smaller than that from the vials from your soil treatments.