Potassium hydrogen phthalate - wikipedia Potassium hydrogen phthalate `` KHPh '' redirects here. For radio station KHPH in Hawaii, see List of radio stations in Hawaii. Potassium hydrogen phthalate Names IUPAC name Potassium hydrogen phthalate Other names hydrogen potassium phthalate ; phthalic acid potassium salt ; potassium biphthalate ; potassium acid phthalate ; 1, 2 - benzenedicarboxylic acid, monopotassium salt ; KHP ; KHPh Identifiers CAS Number 877 - 24 - 7 3D model ( JSmol ) Interactive image ChemSpider 12839 ECHA InfoCard 100.011. 718 PubChem CID 13413 InChI InChI = 1S / C8H6O4. K / c9 - 7 ( 10 ) 5 - 3 - 1 - 2 - 4 - 6 ( 5 ) 8 ( 11 ) 12 ; / h1 - 4H, ( H, 9, 10 ) ( H, 11, 12 ) ; / q ; + 1 / p - 1 Key : IWZKICVEHNUQTL - UHFFFAOYSA - M InChI = 1 / C8H6O4. K / c9 - 7 ( 10 ) 5 - 3 - 1 - 2 - 4 - 6 ( 5 ) 8 ( 11 ) 12 ; / h1 - 4H, ( H, 9, 10 ) ( H, 11, 12 ) ; / q ; + 1 / p - 1 Key : IWZKICVEHNUQTL - REWHXWOFAT SMILES ( K+ ). O = C ( O ) c1ccccc1C ( ( O - ) ) = O Properties Chemical formula C H KO Molar mass 204.22 g mol Appearance White or colorless solid Density 1.636 g / cm Melting point ~ 295 ° C ( decomposes ) Solubility in water 80 g / L ( 20 ° C ) Solubility slightly soluble in alcohol Acidity ( pK ) 5.4 Structure Coordination geometry tetrahedral Hazards Main hazards Irritant to eyes, skin, and respiratory system Safety data sheet External MSDS R - phrases ( outdated ) R36 R37 R38 Flash point Non-flammable Except where otherwise noted, data are given for materials in their standard state ( at 25 ° C ( 77 ° F ), 100 kPa ). Y verify ( what is ? ) Infobox references Potassium hydrogen phthalate, often called simply KHP, is an acidic salt compound. It forms white powder, colorless crystals, a colorless solution, and an ionic solid that is the monopotassium salt of phthalic acid. KHP is slightly acidic, and it is often used as a primary standard for acid - base titrations because it is solid and air - stable, making it easy to weigh accurately. It is not hygroscopic. It is also used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very stable. It also serves as a thermal standard in thermogravimetric analysis. KHP dissociates completely in water, giving the potassium cation ( K ) and hydrogen phthalate anion ( HP or Hphthalate ). As a weak acid hydrogen phthalate reacts reversibly with water to give hydronium ( H O ) and phthalate ions. HP + H O ⇌ P + H O KHP can be used as a buffering agent ( in combination with hydrochloric acid ( HCl ) or sodium hydroxide ( NaOH ) depending on which side of pH 4.0 the buffer is to be ) but should not be used as a buffer for decarboxylation reactions, as these will degrade the KHP and mop up the conjugation groups. KHP is also a useful standard for total organic carbon ( TOC ) testing. Most TOC analyzers are based on the oxidation of organics to carbon dioxide and water, with subsequent quantitation of the carbon dioxide. Many TOC analyzers suggest testing their instruments with two standards : one typically easy for the instrument to oxidize ( KHP ), and one more difficult to oxidize. For the latter, benzoquinone is suggested. References Jump up ^ http://www.merckmillipore.com/INTL/en/product/pharmaceutical-ingredients/potassium-hydrogen-phthalate,MDA_CHEM-104874 Jump up ^ Hendrixson, W.S. ( 1920 ). `` Further Work on Potassium Hydrogen Phthalate as a Standard in Volumetric Analysis ''. J Am Chem Soc. 42 : 724 -- 727. doi : 10.1021 / ja01449a008. Jump up ^ `` Potassium Hydrogen Phthalate ''. Arlington, TX : Ricca Chemical Company. Retrieved 2012 - 10 - 03. Jump up ^ `` The Standardization Of NaOH and KHP Assay '' ( PDF ). Clark College. Archived from the original ( PDF ) on 2012 - 11 - 19. Retrieved 2012 - 10 - 03. Jump up ^ Smalley, I.J., Lill, G.O., Bentley, S.P., Wood, D.R. 1977. Thermogravimetry of potassium hydrogen phthalate and its use as a thermal standard. Canadian Mineralogist 15, 30 - 35 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Potassium_hydrogen_phthalate&oldid=833107098 '' Categories : Carboxylic acids Phthalates Potassium compounds Hidden categories : Articles without EBI source Articles without KEGG source Articles without UNII source ECHA InfoCard ID from Wikidata Chembox having DSD data Articles containing unverified chemical infoboxes Talk About Wikipedia تۆرکجه Deutsch Español فارسی Français Italiano עברית Nederlands Português සිංහල Српски / srpski Srpskohrvatski / српскохрватски Türkçe 中文 5 more Edit links This page was last edited on 29 March 2018, at 18 : 19 ( UTC ). About Wikipedia

Question: characteristics of khp that make it qualify as a primary standard
Answer: because it is solid and air-stable, making it easy to weigh accurately