Nitric Acid 100%

１）都是發煙硝酸
The pure acid tends to give off white fumes when exposed to air, leading to the common name "fuming nitric acid
２）硝酸可以不帶有nitrogen oxides，是透明液體。當帶有nitrogen oxides，才變成黃色的。
Pure anhydrous nitric acid (100%) is a colorless liquid with a density of 1522 kg/m^3 which solidifies at -42 deg C to form white crystals and boils at 83 deg C. When boiling in light, even at room temperature, there is a partial decomposition with the formation of nitrogen dioxide following the reaction:
4HNO3 → 2H2O + 4NO2 + O2 (72 deg C)
which means that anhydrous nitric acid should be stored below 0 deg C to avoid decomposition. The nitrogen dioxide (NO2) remains dissolved in the nitric acid coloring it yellow, or red at higher temperatures.
３）用降氣壓（半真空）的方法，使nitrogen oxides自然排走。
The dissolved NOx are readily removed using reduced pressure at room temperature (10-30 min at 200 mmHg or 27 kPa). Obtained white fuming nitric acid has density 1.51 g/cm^3. This procedure can also be performed under reduced pressure and temperature in one step in order to produce less nitrogen dioxide gas.
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