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I know $\ce{NaOH}$ can absorb $\ce{NO2}$, but I could not find any data of solubility of $\ce{NO2}$ in $\ce{NaOH}$ at room temperature and atmospheric pressure.

I am trying to figure out how much NaOH solution I will need to absorb the $\ce{NO2}$ gas being produced from a result of another reaction. My setup is having $\ce{NaOH}$ solution in a beaker (how much is what I want to calculate) and feed in the $\ce{NO2}$ gas into the solution. Is there any way to theoretically calculate the quantity of $\ce{NaOH}$ I will need to absorb the $\ce{NO2}$ gas without solubility data?

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    $\begingroup$ NO2 reacts with NaOH, forming NaNO2 + NaNO3, so solubility does not make sense. $\endgroup$
    – Poutnik
    Nov 28 '21 at 7:05
  • $\begingroup$ You may find useful these links for text formatting ( not to be applied to titles ): notation , formulas/expressions/equations and upright vs italic $\endgroup$
    – Poutnik
    Nov 28 '21 at 7:46
  • $\begingroup$ @Poutnik Relevant line of argument: chemistry.stackexchange.com/questions/42696/… $\endgroup$ Nov 28 '21 at 9:39
  • $\begingroup$ @NilayGhosh Well, bromine water is in very majority a true solution, with the equilibrium strongly shifted to the left. For NO2/NaOH, it is the opposite. $\endgroup$
    – Poutnik
    Nov 28 '21 at 9:50
  • $\begingroup$ By other words, practically, it is possible to achieve saturated solution Br2(l)<=>Br2(g)<=>Br2(aq), but not NO2(g)<=>[NaOH]NO2(aq). NO2 or NaOH will be spent. $\endgroup$
    – Poutnik
    Nov 28 '21 at 10:31
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A numerous studies have shown that the absorbtion of $\ce{NO2}$ in alkaline solutions is due to the reaction (For example, Ref.1):

$$\ce{2NO2 + 2OH- -> NO2- + NO3- + H2O} \tag1$$

Thus, as Poutnik pointed out, you may use dilute solution of $\ce{NaOH}$ solution, if you preferred. For insterd, Ref.2 has used sodalime, mainly $\ce{Ca(OH)2}$, in its solid form (following is the method in the paper for your benefit):

The test gas containing $\ce{NO2}$ $\pu{57 ppm}$ in high purity nitrogen and a trace of oxygen was passed at a flow rate of $\pu{1 litre min-1}$ through the column filled with soda lime $\pu{120 g}$ (Soda sorb) and the $\ce{NO2}$ concentration was measured continuously at the outlet of the column by an electrochemical fuel cell technique (TM-100, Taiyo-Sanso, Co., Ltd, Osaka). Break point was determined as the time when $5\%$ of the initial concentration of $\ce{NO2}$ was detected.

The authors have used two different varieties of soda limes, Soda sorb (which has the chemical composition of $73\% \ \ce{Ca(OH)2}, 5\% \ \ce{KOH}, 3\% \ \ce{NaOH}$, and less than $19\% \ \ce{H2O}$ with ethyl violet colour indicator) and Wako lime-A (which has the chemical composition of $81\% \ \ce{Ca(OH)2}, 4\% \ \ce{NaOH}$, and $15\% \ \ce{H2O}$ with ethyl violet colour indicator). The difference between these two types is the absence of $\ce{KOH}$ in Wako lime-A. The authors have claimed that they have shown that soda lime completely absorbed $\ce{NO2}$ regardless of the type of soda lime used. Thus, it is safe to suggest that the only necessity is the presence of $\ce{OH-}$ in the system.

Further, according to Ref.2, following equilibrium would establishe in aqeous medium:

$$\ce{2NO2(g) + H2O (l) <=> HNO2 (aq) + NO3- (aq) + H+ (aq)} \tag2$$

The following is the best result of particular experiment measuring the absorption of $\ce{NO2}$ (for example, flue gas used: $\pu{800 ppm}$ $\ce{NO2}$ in $\ce{N2}$ with flowrate of $\pu{1 L/min}$) in caustic aqueous scrubbing solution, which, for example, is $\pu{1 L}$ of $\pu{0.5 M}$ $\ce{NaOH}$ for the best result (all experiments have been conducted at room temperature and pressure). The average percent absorption $(n = 3)$ is reported as $98.1\%$ in $\pu{0.5 M}$ $\ce{NaOH}$ solution. For compartion, it was reported as $89.9\%$ in $\pu{0.1 M}$ $\ce{NaOH}$ solution and $81.8\%$ in $\pu{0.01 M}$ $\ce{NaOH}$ solution. Thus, even though change in absorption varies from different concentration of $\ce{NaOH}$ used, the difference is close enough to say concentration would not be effective if you have increased the time of exposure of gas to the scrubbing solution.

References:

  1. T. Ishibe, T. Sato, T. Hayashi, N. Kato, and T. Hata, "Absorption of nitrogen dioxide and nitric oxide by soda lime," British Journal of Anaesthesia 1995, 75(3), 330-333 (DOI: https://doi.org/10.1093/bja/75.3.330)(PDF).
  2. Chen-Lu Yang, "Aqueous Absorption of $\ce{NO_x}$ Induced by Sodium Chlorite Oxidation," Master's Thesis 1989, New Jersey Institute of Technology, NJ.
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