Double distilled water: Difference between revisions
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#REDIRECT [[Purified water#Double distillation]] |
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'''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. |
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Modern molecular biology labs typically use water purification systems such as [[Milli-Q]] to create ultra-pure water. |
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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 [[carbon dioxide]] (CO<sub>2</sub>) that is absorbed from the atmosphere. Dissolved carbon dioxide reacts slowly with water to give the [[bicarbonate]] and [[hydronium]] ions. |
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:CO<sub>2</sub> + 2H<sub>2</sub>O <math>\rightleftharpoons</math> HCO<sub>3</sub><sup>-</sup> + H<sub>3</sub>O<sup>+</sup> |
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([[carbonic acid]], H<sub>2</sub>CO<sub>3</sub>, is only formed in strongly acid solutions). 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. |
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==See also== |
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* [[Distilled water]] |
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* [[Deionized water]] |
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[[Category:Liquid water]] |
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[[Category:Distillation]] |
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[[pl:Woda redestylowana]] |
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Latest revision as of 10:41, 29 April 2018
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