Nitrogen dioxide color

Nitrogen Dioxide a gas (NOj) consisting of one nitrogen and two oxygen atoms. It absorbs blue light and therefore has a reddish-brown color associated with it. 

Some of the substances you work with in general chemistry can be identified at least tentatively by their color. Gaseous nitrogen dioxide has a brown color vapors of bromine and iodine are red and violet, respectively. A water solution of copper sulfate is blue, and a solution of potassium permanganate is purple (Figure 1.14). 

Consider what happens when a sample of N204, a colorless gas, is placed in a closed, evacuated container at 100°C. Instantly, a reddish-brown color develops. This color is due to nitrogen dioxide, NO2, harmed by decomposition of part of the N2O4 (Figure 12.1, p. 324) ... 

We have not yet distinguished the gases nitric oxide, hydrogen, and oxygen. Nitric oxide has its own personality. Immediately upon exposure to air, the colorless nitric oxide becomes reddish-brown—exactly the color of nitrogen dioxide. Neither oxygen nor hydrogen behaves this way. 

The particles, or molecules, of the gas nitric oxide cannot be exactly like those of nitrogen dioxide. There must be differences that account for the fact that one gas is colorless and the other reddish-brown. Yet, when nitric oxide and air are mixed, color appears, suggesting that nitrogen dioxide has been formed. Apparently molecules present in air somehow combine with the molecules of nitric oxide to form molecules of nitrogen dioxide. We would like to develop our picture of molecules so it will aid us in discussing these changes. 

Consider the combination of nitric oxide and oxygen. Nitric oxide (a colorless gas) when mixed with oxygen gas (also colorless) becomes reddish-brown. The color is identical to that of another gas, nitrogen dioxide. All the properties of the nitric oxide-oxygen mixture are consistent with the conclusion that the gas nitrogen dioxide has... 

Nitrogen dioxide, N02 (oxidation number -t-4), is a choking, poisonous, brown gas that contributes to the color and odor of smog. The molecule has an odd number of electrons, and in the gas phase it exists in equilibrium with its colorless dimer N204. Only the dimer exists in the solid, and so the brown gas condenses to a colorless solid. When it dissolves in water, NOz disproportionates into nitric acid (oxidation number +5) and nitrogen oxide (oxidation number +2) ... 

Nitrogen dioxide, a red-brown gas, is stable at room temperature. However, Figure 15-1 shows that reducing the temperature causes a sample of NO2 to become colorless. The color change that happens at low temperature occurs because two NO2 molecules combine to form one molecule of a colorless gas, N2 O4. ... 

Electron-transfer activation. The observation of intense coloration upon mixing the solutions of hydroquinone ether MA and nitrogen dioxide at low temperature derives from the transient formation of MA+ cation radical, as confirmed by the spectral comparison with the authentic sample. The oxidation of MA to the corresponding cation radical is effected by the nitrosonium oxidant, which is spontaneously generated during the arene-induced disproportionation of nitrogen dioxide,239 i.e.,... 

Before 1970, most of the data for nitrogen oxides were obtained by continuous measurements with a colorimetric analyzer that was similar in principle to the colorimetric oxidant analyzer shown in Figure 6-8. The scrubbing agent is a mixture of -(l-naphthyl)ethylenediamine, sulfanilic acid, and acetic acid in aqueous solution. The color is produced when both nitrogen dioxide and nitrites react with this reagent to form an azo dye. The color is not affected by nitric oxide in the air sample. 

Nitrogen dioxide can be identified by color, odor, and physical properties. It is dissolved in warm water and converted to nitric acid. The latter may be measured by acid-base titration or from analysis of nitrate ion by nitrate ion-specific electrode or by ion chromatography. Alternatively, nitrogen dioxide may be passed over heated charcoal to produce nitrogen and carbon dioxide that may be analysed by GC-TCD or GC/MS (See Nitrogen, Analysis). The characteristic masses for N2 and CO2 formed for their identification are 28 and 44, respectively. 

Nitrogen tetroxide may be identified from physical and chemical properties and its ready conversion to NO2 gas which may be identified by its brown red color, pungent odor, and chemical analysis (See Nitrogen Dioxide, Analysis.)... 

When a sample of N2O4, a colorless and poisonous gas, is placed in a closed container, a reddish-brown color develops due to the presence of nitrogen dioxide, NO2. As soon as some NO2 is formed, the reverse reaction can occur simultaneously with the forward reaction. 

At low acid concentrations, nitric oxide tends to form. This evidently may attack nitrosophenol to form diazonium compounds directly. The diazonium salts, in turn, may couple with unreacted phenol to give colored products. Nitrous acid may also produce nitrophenols from phenols. The mechanism of this reaction may involve oxidation of initially formed nitrosophenols, homolytic attack by nitrogen dioxide, or nucleophilic attack by nitrite ions [1]. 

A S320 Nitrogen dioxide 5 TEA coated Molecriar TEA Sieve Color. 3.1-11.5 ppm... 

Nitrogen dioxide is a powerful corrosive agent that acts on metal, stone, and even human tissue. Its brown color is responsible for the brown haze typically seen over a polluted city. 

Whitmore, P.M. and Cass, G.R. (1989) The fading of artists colorants by exposure to atmospheric nitrogen dioxide. Studies in Conservation, 34, 85-97. 

Nitrogen dioxide is a red-brown gas that is very soluble in water. It has an unpleasant odor and is quite poisonous. When nitrogen dioxide is cooled, its brown color fades to a pale yellow. Molecular weight determinations show that this yellow substance has a formula of N2O4 (nitrogen tetroxide) ... 

This means that anhydrous nitric acid should be stored below 0°C to avoid decomposition. The nitrogen dioxide remains dissolved in the nitric acid and creates a yellow color at room temperature and a red color at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors which leads to the common name red fuming acid 53. 

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