Primary standard 200069 225665328 2008-07-14T20:19:51Z Chetvorno 1030826 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]]