Mechanism of the NO2 Conversion to NO2− in an Alkaline Solution

Abstract

The reaction of NO2 and NaOH aqueous solution at room temperature was studied for elucidating the behavior of gaseous NO2 in an alkaline solution. Experimental runs related to NO2 absorption have been carried out in various pH solutions. The nitrite and nitrate ions formed in these absorption solutions were quantitatively analyzed. In the case of pH 5 -12, both of the nitrite and nitrate ions were formed simultaneously. On the other hand, only the nitrite ion was formed when the pH of the absorption solution was higher than 13. In this paper, a new reaction mechanism was proposed to explain the selective formation of nitrite ion in the 10 M alkaline solution. In order to confirm the new reaction mechanism, H2 18 O was used as part of the absorption solution for detecting oxygen gas production.

Formation of Nitrite- and Nitrate-Ions in Aqueous Solutions Treated with Pulsed Electric Discharges

“…In acidic solutions, nitrates are formed mostly in the disproportioning reaction [3] and, to some extent, in Equations [4-6]. The increased pH results in a greater role of reaction [12] described by Chen et al (2004):…”

Effects of NOX and O2 on the Reaction of Ca(OH)2 with CO2 at Low Temperatures

“…As NO 2 is a much stronger oxidant and more soluble in water than NO and O 2 , more NO 2 would be absorbed into the water layer on the Ca­(OH) 2 surface. NO 2 would react with water to form HNO 2 , HNO 3 , NO 2 – , NO 3 – , and H + . ,, NO 2 molecules would also react with OH – ions produced by the dissolution of Ca­(OH) 2 from the surface underneath the water layer to form NO 2 – . As OH – in the water layer was depleted by reacting with NO 2 and H + , H + would continue to react with Ca­(OH) 2 at the water-solid interface.…”

“…15,18,23 NO 2 molecules would also react with OH − ions produced by the dissolution of Ca(OH) 2 from the surface underneath the water layer to form NO 2 − . 24 As OH − in the water layer was depleted by reacting with NO 2 and H + , H + would continue to react with Ca(OH) 2 at the water-solid interface. Ca 2+ would react with NO 2 − and NO 3 − to form Ca(NO 2 ) 2 and Ca(NO 3 ) 2 ; both salts are deliquescent, and the latter is more soluble in water.…”

“…As mentioned above, for the reaction of Ca(OH) 2 with NO 2 /O 2 , X N1 was much greater than X N2 . The reason may be that the presence of NO in the gas phase would enhance the formation of HNO 2 (the backward reaction of eq 4) and the dissolution of Ca(OH) 2 would keep the water layer in alkaline condition, thus the amount of NO 2 − would be more than that of NO 3 − (see eq 2), 24 resulting in the fraction of Ca(NO 2 ) 2 being much greater than that of Ca(NO 3 ) 2 .…”