Determination of the Ionic Association Constants of Na+ with CO32− and HCO3− Ions, in NaCl-NaHCO3-H2O Ternary Systems, at 25 °C
Round 1
Reviewer 1 Report
The manuscript "Determination of Ionic Association Constants of Na+ with CO32- and HCO3- Ions, in NaCl‒NaHCO3‒H2O Ternary Systems, at 25 0C" focuses on determining the association constants of sodium ion and carbonate and hydrocarbonate anions in aqueous medium at different ionic strength values. Authors applied reliable procedure to determine the mean activity coefficients of NaCl in binary system, containing also NaHCO3, and calculated the association constants from the observed deviation of the predicted activity coefficients from the observed ones. The manuscript is clear and sound, however, I feel there is some room for improvement according to the following points:
1. Can a reliable extrapolation of Kc1 and Kc2 to zero ionic strength value be made? It seems that the shape of fitting curves represented on Figs. 4, 5 depends strongly on two left points (the reliability of their determination). What are the errors of fitting parameters?
2. Can the dependecies of Kci on IE be fitted by the following equation (Kci = A + B*IE + C*IE^0.5) instead of quadratic function? The mentioned equation which uses the power of 0.5 for the ionis strength value was successfully used earlier for fitting of the dependencies of rate constants (10.1016/j.marchem.2009.07.004) and formal electrode potential (10.1016/S0039-9140(98)00022-8). Could you test this model as well?
3. What is the yield of associated species at different ionic strength values? I believe the speciation diagrams should be plotted to show it. They can be added to the supplementary materials.
4. If the yield of associated species is significant, their existence can be confirmed using, e.g., IR spectroscopy. Free (or evenly surrounded by water molecules) carbonate is of D3h symmetry group posessing three peaks in IR or Raman spectra. Association leads to decrease in symmetry and increase in spectral lines quantity (see e.g. 10.1016/j.gsf.2020.03.002)
5. In the introduction, among the software packages available for chemical speciation calculation and graphical representation, one more can be noted (10.1016/j.talanta.2019.01.107)
6. I also know of two papers that seem relevant to the research topic (10.1023/A:1022696726873, 10.1021/j100707a026) and two theses (https://thekeep.eiu.edu/theses/3271, https://thekeep.eiu.edu/theses/3208), and, perhaps, there are more. I'd expand an Introduction a little giving more complete data on literature association constants. Perhaps, a comparative table is in order.
7. It is not recommended to calibrate the electrodes using buffer solutions at I>0.1 mol/L because formal potential and protolytic equilibria of buffers are dependent on I; although it had been shown that the influence is negligible in the range of I = 0.1-1.0 mol/L (10.1021/acs.jced.2c00034)
Author Response
Dear Sir/Madame
We would like to thank our reviewer for the time taken to read and analyze our manuscript and for the suggestions given. Thanks to your contribution we consider that our paper is in a much better form. The new manuscript version considers all comments received. Please find in attachment all comments received.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This investigation reports the measurements of the ionic association constants of sodium with carbonate ions and acidic carbonate ions in the ternary system NaCl‒NaHCO3‒H2O. The mean activity coefficients of sodium chloride (in pure solution and in a mixture) were determined using electrochemical cells. Harned's rule is used for the ternary system.
It’s an interesting work, and I have some comments. I think that these comments are meant to be constructive for the quality of the paper.
· Rewrite the introduction by regrouping the sentences.
· Give the broad outlines of the approach and the bases of applied software; more detail and an explanation of speciation software packages should be given.
· All the references are not written in homogenous form.
Some mistakes in the text
Author Response
Dear Sir/Madame
We would like to thank you for the time taken to read and analyze our manuscript and for the suggestions given. Thanks to your contribution we consider that our paper is in a much better form. The new manuscript version considers all comments received. Please find in attachment all comments received.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors have revised a manuscript thoroughly and answered all the questions in the most convincing manner. I support publishing of the paper in its current version.
