Distilled water is water purified from mineral salts, organic substances and other impurities dissolved in it by distillation [1] . According to Russian GOST 6709-72, the mass concentration of the residue after evaporation of distilled water should be no more than 5 mg / dm 3 , the pH should be in the range of 5.4-6.6, the electrical conductivity at 20 ° C should be no more than 5 · 10 −4 S / m [2] (corresponds to a specific electrical resistance of 2 kΩ⋅m).
Content
Features
Distilled water in the Russian Federation is standardized on the basis of GOST 6709-72 "Distilled water."
Physical Properties
The electrical conductivity of distilled water is small (GOST 6709-72 requires no more than 0.5 mS / m [3] ).
Atmospheric gases are dissolved in distilled water: oxygen, nitrogen, argon, carbon dioxide and a small amount of others. Due to dissolved carbon dioxide, distilled water has a slightly acidic environment and its pH is 5.4–6.6. To obtain completely neutral water, it is boiled until carbon dioxide is completely removed (within 30 minutes) and stored in an airtight container.
Features
Being very clean, in the absence of extraneous mechanical impurities it can be overheated above the boiling point , or supercooled below the freezing point without effecting a phase transition . The phase transition occurs intensively with the introduction of mechanical impurities or shaking.
Usage
The main use of distilled water is chemical laboratories, where it is used for the preparation of solutions, analysis and rinsing of chemical dishes after washing
Distilled water itself is potable. In 2011, the World Health Organization noted that there is not enough data to establish lower (and upper) limits of water hardness [4] . However, since drinking water can be an important source of calcium and magnesium for some categories of the population (for which other sources of these minerals are limited), when using demineralized water in water sources, it is recommended to add calcium and magnesium salts to the levels observed in natural water in a given area [4] .
They are used to adjust the density of electrolytes , safe operation of batteries , flushing liquid cooling systems, diluting concentrates of various liquids and for other household needs. For example, for adding to steam irons (completely exclude the appearance of scale), for adjusting the freezing temperature of non-freezing glass washer fluid and for color photo printing .
Water that meets the requirements for distilled water can be obtained, in addition to distillation, also by ion exchange methods, reverse osmosis, a combination of these methods, or some others.
History
Drinking water has been distilled from seawater since at least about 200 g. e., when the process was clearly described by Alexander of Aphrodisia . Aristotle in his treatise Meteorology (II.3, 358b16) also speaks of distillation of water [5] .
Double-distilled water
Double-distilled water - twice purified water. Obtained by distillation of distilled water in a quartz apparatus - redistillator. Its properties are close to chemically pure water. Due to the high degree of purification during storage and use, special precautionary measures must be taken to eliminate the possibility of contamination of bidistilled water. Used when working with substances of high purity.
Further Cleaning
For further purification (from volatile organic impurities), bidistillates are irradiated with gamma radiation . After irradiation, water is purged with purified argon to remove radiolysis products (primarily carbon dioxide ).
See also
- Deionized water
Notes
- ↑ Chemical encyclopedia. - M .: Soviet Encyclopedia. Ed. I. L. Knunyantsa. 1988. - article "Distilled water"
- ↑ GOST 6709-72
- ↑ Chemical and physical indicators of distilled water according to GOST 6709-72 .
- ↑ 1 2 Hardness in Drinking-water . World Health Organization 2011. (English)
- ↑ Aristotle. Meteorology - Book II (PDF). University of Adelaide. .