Nitrogen is a chemical element of the periodic system, denoted by the letter N and having the serial number 7. It exists in the form of an N2 molecule consisting of two atoms. This chemical is a colorless, odorless and tasteless gas; it is inert under standard conditions. The density of nitrogen under normal conditions (at 0 ° C and a pressure of 101.3 kPa) is 1.251 g / dm3. The element is part of the Earth’s atmosphere in the amount of 78.09% of its volume. It was first discovered as an air component by Scottish physician Daniel Rutherford in 1772.
Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at a temperature of 195.8 ° C. Therefore, it can only be stored in isolated vessels, which are steel cylinders for liquefied gases or Dewar vessels. Only in this case can it be stored or transported without much loss due to evaporation. Like dry ice (liquefied carbon dioxide, also called carbon dioxide), liquid nitrogen is used as a refrigerant. In addition, it is used for cryopreservation of blood, germ cells (sperm and ova), as well as other biological samples and materials. It is also in demand in clinical practice, for example, in cryotherapy when removing cysts and warts on the skin. The density of liquid nitrogen is 0.808 g / cm3.
Many industrially important compounds, such as nitric acid, ammonia, organic nitrates (explosives, fuels) and cyanides, contain N2. The extremely strong bonds of elemental nitrogen in the molecule cause difficulties for its participation in chemical reactions, this explains its inertness under standard conditions (temperature and pressure). Including for these reasons, N2 is of great importance in many scientific and industrial fields. For example, it is necessary to maintain in-situ pressure during oil or gas production. Any practical or scientific application requires knowing what the density of nitrogen will be at a particular pressure and temperature. From the laws of physics and thermodynamics it is known that at a constant volume, pressure and gas density will increase with increasing temperature , and vice versa.
When and why you need to know the density of nitrogen? The calculation of this indicator is used in the design of technological processes taking place with the use of N2, in laboratory practice and in production. Using the known value of the gas density, it is possible to calculate its mass in a certain volume. For example, it is known that gas under normal conditions occupies a volume of 20 dm3. In this case, its mass can be calculated: m = 20 • 1.251 = 25.02 g. If the conditions are different from the standard ones and the volume N2 is known under these conditions, you will first need to find (from the references) the nitrogen density at a certain pressure and temperature, and then multiply this value by the volume occupied by the gas.
Similar calculations are carried out in production when compiling material balances of technological installations. They are necessary for the conduct of technological processes, the selection of instrumentation, the calculation of technical and economic indicators and so on. For example, after stopping the chemical production, all devices and pipelines must be purged with an inert gas, nitrogen, before they are opened and taken out for repair (it is the cheapest and most affordable compared to, for example, helium or argon). As a rule, they are purged with such amount of N2, which is several times larger than the volume of apparatus or pipelines, only in this way can combustible gases and vapors be removed from the system and an explosion or fire can be excluded. When planning operations before a stop repair, the technologist, knowing the volume of the system to be emptied and the density of nitrogen, calculates the mass N2, which will be required for purging.
For simplified calculations that do not require accuracy, real gases are equated with ideal gases and the Avogadro law is applied. Since the mass of 1 mol of N2 is numerically equal to 28 grams, and 1 mol of any ideal gas occupies a volume of 22.4 liters, the nitrogen density will be equal to: 28 / 22.4 = 1.25 g / l = 1.25 g / dm3. This method of quickly finding the density is applicable to any gas, not just N2. It is often used in analytical laboratories.