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#REDIRECT [[Purified water#Double distillation]]
'''Double distilled water''' (abbreviated "ddH<sub>2</sub>O" or "Bidest. water") is prepared by double [[distillation]] of water. It is used, among other things, when single distillation does not lead to sufficiently pure water for some applications in [[biochemistry]].


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Bidest. water is used when pure, sterile water is essential. Whereas distilled water is enough for most chemical reactions, a [[molecular biologist]] attempting to create sterile, [[enzyme]]-free media might use bidest. water to ensure sterility.

Modern molecular biology labs typically use water purification systems such as [[Milli-Q]] to create ultra-pure water.

The theoretical pH of distilled water is 7.0. In practice, however, most distilled water will have a pH that is slightly acidic (less than 7.0) due to the presence of dissolved carbon dioxide (CO<sub>2</sub>) that is absorbed from the atmosphere and which forms carbonic acid (H<sub>2</sub>CO<sub>3</sub>) in water. During distillation, the dissolved CO<sub>2</sub> will be driven out of the liquid. However, during condensation the water will re-absorb the CO<sub>2</sub> again resulting in a pH that is less than 7.0.

==See also==
* [[Distilled water]]
* [[Deionized water]]

[[Category:Liquid water]]
[[Category:Distillation]]

[[pl:Woda redestylowana]]

Latest revision as of 10:41, 29 April 2018