Primary standard
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2008-07-14T20:19:51Z
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Minor wording change, first sentence
In [[metrology]], a '''primary standard''' is a [[standard (technical)|standard]] that is accurate enough that it is not calibrated by or subordinate to other standards. A '''primary standard''' in [[chemistry]] is a reliable, readily quantified substance. Features of a primary standard include:
<p>1. High [[purity]]
<br>2. Stability (low [[reactivity]])
<br>3. Low [[hygroscopicity]] and [[efflorescence]]
<br>4. High [[solubility]] (if used in [[titration]])
<br>5. High [[equivalent weight]]
<p>Some examples of primary standards according to the [[European Pharmacopoeia]] 5, ch. 4.2:
*[[Arsenic trioxide]] for making [[sodium arsenite]] solution for standardisation of [[sodium periodate]] solution (until Ph. Eur. 3, Appendix 2001 also for [[iodine]] and [[cerium(IV) sulfate]] solutions, since Ph. Eur. 4, 2002 standardised by [[sodium thiosulfate]])
*[[Benzoic acid]] for standardisation of [[waterless]] basic solutions: [[ethanol]]ic [[sodium hydroxide|sodium]] and [[potassium hydroxide]], [[tetrabutylammonium hydroxide|TBAH]], and [[alkali methanolate]]s in [[methanol]], [[isopropanol]], or [[DMF]]
*[[Potassium bromate]] (KBrO<sub>3</sub>) for standardisation of [[sodium thiosulfate]] solutions
*[[Potassium hydrogen phthalate]] (usually called KHP) for standardisation of aqueous base and [[perchloric acid]] in [[acetic acid]] solutions
*[[Sodium carbonate]] for standardisation of [[aqueous]] acids: [[hydrochloric acid|hydrochloric]], [[sulfuric acid]] and [[nitric acid]] solutions (but not [[acetic acid]])
*[[Sodium chloride]] for standardisation of [[silver nitrate]] solutions
*[[Sulfanilic acid]] for standardisation of [[sodium nitrite]] solutions
*[[Zinc]] powder, after being dissolved in sulfuric or hydrochloric acid, for standardisation of [[EDTA]] solutions
==External links==
*[http://www.chemistry.adelaide.edu.au/external/soc-rel/content/standard.htm Analytical Standards]
Primary standard is used in titration.
A primary standard must contain the following,
1. high purity
2. atmospheric stability
3. absence of hydrate water
4. modest cost
5. reasonable solubility
6. reasonably high molar mass
Source : Skook, West, Holler, Crouch "Fundamentals of Analytical Chemistry" Brooks/ Cole. California, 2004
==Source==
*Skoog and West. Fundamentals of Analytical Chemistry. (3rd ed.) Holt, Rinehart, and Winston, 1976.
[[Category:Analytical chemistry]]
[[de:Urtitersubstanz]]
[[es:PatrĂ³n primario]]