1) Describe of properties, technology of production and analysis of Кrypton.

Krypton is chemical element number 36 on the periodic table of the elements. It belongs to the group of elements known as the noble gases. Under normal conditions, krypton is a colorless, tasteless, odorless gas. Its density at normal temperature and pressure is about 0.5 oz per gallon (3.7 g per liter), making it nearly three times heavier than air. At extremely low temperatures, krypton may exist as a liquid or a solid. The boiling point of krypton is -243.81° F (-153.23° C), and its freezing point is only slightly lower at -251.27° F (-157.37° C).

Natural krypton is a mixture of six stable isotopes. The isotopes of krypton all have 36 protons and are named for their atomic weights. Krypton-84, which has 48 neutrons, is the most common isotope and makes up 57% of natural krypton. The other stable isotopes of krypton are krypton-86 (50 neutrons, 17.3%); krypton-82 (46 neutrons, 11.6%); krypton-83 (47 neutrons, 11.5%); krypton-80 (44 neutrons, 2.25%); and krypton-78 (42 neutrons, 0.35%)

Krypton can also exist as an unstable, radioactive isotope. These isotopes are created during nuclear reactions. About 20 radioactive isotopes of krypton have been produced. All of these isotopes except krypton-85 are very unstable, with half-lives of a few hours or less. (The half-life of a radioactive substance is the time required for half of the atoms in a sample of the substance to undergo radioactive decay.) Krypton-85, which has 36 protons and 49 neutrons, is much more stable, with a half-life of 10.73 years.

Krypton is used with argon in fluorescent lights to improve their brightness and with nitrogen in incandescent lights to extend their lifetime. It is also used in flashbulbs to produce a very bright light for a very short period of time, for use in high-speed photography. Radioactive krypton-85 can be used to locate small flaws in metal surfaces. The gas tends to collect in these flaws and its radioactivity can be detected.

Although traces of krypton are found in various minerals, the most important source of krypton is Earth's atmosphere.

Krypton can also be obtained from the fission of uranium, which occurs in nuclear power plants. Unlike air, which contains only the stable isotopes of krypton, this process produces both stable isotopes and radioactive isotopes of krypton.

The Manufacturing Process

Making liquid air

1 Air is first passed through filters to remove particulate matter such as dust. The clean air is then exposed to an alkali (a strongly basic substance), which removes water and carbon dioxide.

2 The clean, dry air is compressed under high pressure. Because compression raises the temperature of the air, it is then cooled by refrigeration.

3 The cooled, compressed air passes through coils winding through an empty chamber. A portion of the air, which is compressed to a pressure about two hundred times greater than normal, is allowed to expand into the chamber. This sudden expansion absorbs heat from the coils, cooling the compressed air. The process of compression and expansion is repeated until the air has been cooled to a temperature of about -321 F (-196° C), at which point most of the gases in the air are transformed into liquids.

Separating the gases

4 Gases with very low boiling points are not transformed into liquids and can be removed from the others directly. These gases include helium, hydrogen, and neon.

5 A process known as fractional distillation separates the various elements found in liquid air. This process relies on the fact that the different substances will be transformed from liquid to gas at different temperatures.

6 The liquid air is allowed to warm slowly. As the temperature increases the substances with the lowest boiling points become gases and can be removed from the remaining liquid. Argon, oxygen, and nitrogen are the first substances to be transformed into gases as the liquid air warms. Krypton and xenon have higher boiling points and remain in the liquid state when the other components of air have become gases.

Separating krypton from xenon

7 The liquid krypton and xenon are absorbed onto silica gel or onto activated charcoal. They are then once again subjected to fractional distillation. The liquid mixture is warmed slowly until the krypton is transformed into a gas. The xenon has a somewhat higher boiling point and remains behind as a liquid.

8 The krypton is purified by passing it over hot titanium metal. This substance tends to remove all elements except noble gases.