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'''Potassium hydrogen phthalate''', often called simply '''KHP''', is an acidic salt compound. It forms white powder, colorless crystals, a colorless solution, and an ionic ] that is the ] salt of ]. KHP is slightly ]ic, and it is often used as a ] for ]s because it is solid and air-stable, making it easy to weigh accurately. It is not ].<ref>{{cite journal |last= Hendrixson|first= W. S. |year=1920 |title= Further Work on Potassium Hydrogen Phthalate as a Standard in Volumetric Analysis |journal=J Am Chem Soc |volume= 42 |issue= 4 |pages= 724–727 |doi=10.1021/ja01449a008|url= https://zenodo.org/record/1428826 }}</ref><ref>{{cite web |url= http://www.riccachemical.com/Technical-Support/Tech-Tips/Potassium_Hydrogen_Phthalate |title= Potassium Hydrogen Phthalate |publisher= Ricca Chemical Company |location= Arlington, TX |accessdate= 2012-10-03 |archive-url= https://web.archive.org/web/20121130163435/http://www.riccachemical.com/Technical-Support/Tech-Tips/potassium_hydrogen_phthalate |archive-date= 2012-11-30 |url-status= dead }}</ref><ref>{{cite web |url= http://web.clark.edu/nfattaleh/classes/135/Sp05/Labs/NaOHStdSp05.pdf |title= The Standardization Of NaOH and KHP Assay |publisher= Clark College |accessdate= 2012-10-03 |url-status= dead |archiveurl= https://web.archive.org/web/20121119094358/http://web.clark.edu/nfattaleh/classes/135/Sp05/Labs/NaOHStdSp05.pdf |archivedate= 2012-11-19 }}</ref> It is also used as a primary standard for calibrating ]s because, besides the properties just mentioned, its ] in solution is very stable. It also serves as a thermal standard in ].<ref> 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</ref> '''Potassium hydrogen phthalate''', often called simply '''KHP''', is an acidic salt compound. It forms white powder, colorless crystals, a colorless solution, and an ionic ] that is the ] salt of ]. KHP is slightly ]ic, and it is often used as a ] for ]s because it is solid and air-stable, making it easy to weigh accurately. It is not ].<ref>{{cite journal |last= Hendrixson|first= W. S. |year=1920 |title= Further Work on Potassium Hydrogen Phthalate as a Standard in Volumetric Analysis |journal=J Am Chem Soc |volume= 42 |issue= 4 |pages= 724–727 |doi=10.1021/ja01449a008|url= https://zenodo.org/record/1428826 }}</ref><ref>{{cite web |url= http://www.riccachemical.com/Technical-Support/Tech-Tips/Potassium_Hydrogen_Phthalate |title= Potassium Hydrogen Phthalate |publisher= Ricca Chemical Company |location= Arlington, TX |accessdate= 2012-10-03 |archive-url= https://web.archive.org/web/20121130163435/http://www.riccachemical.com/Technical-Support/Tech-Tips/potassium_hydrogen_phthalate |archive-date= 2012-11-30 |url-status= dead }}</ref><ref>{{cite web |url= http://web.clark.edu/nfattaleh/classes/135/Sp05/Labs/NaOHStdSp05.pdf |title= The Standardization Of NaOH and KHP Assay |publisher= Clark College |accessdate= 2012-10-03 |url-status= dead |archiveurl= https://web.archive.org/web/20121119094358/http://web.clark.edu/nfattaleh/classes/135/Sp05/Labs/NaOHStdSp05.pdf |archivedate= 2012-11-19 }}</ref> It is also used as a primary standard for calibrating ]s because, besides the properties just mentioned, its ] in solution is very stable. It also serves as a thermal standard in ].<ref>{{Cite journal |last=Smalley |first=I.J. |last2=Lill |first2=G.O. |last3=Bentley |first3=S.P. |last4=Wood |first4=D.R. |date=1977 |title=Thermogravimetry of potassium hydrogen phthalate and its use as a thermal standard |url=https://pubs.geoscienceworld.org/canmin/article-abstract/15/1/30/11172/Thermogravimetry-of-potassium-hydrogen-phthalate |journal=Canadian Mineralogist |volume=15 |issue=1 |pages=30-35}}</ref>


KHP dissociates completely in water, giving the potassium cation (K<sup>+</sup>) and hydrogen phthalate anion (HP<sup>−</sup> or Hphthalate<sup>−</sup>) KHP dissociates completely in water, giving the potassium cation (K<sup>+</sup>) and hydrogen phthalate anion (HP<sup>−</sup> or Hphthalate<sup>−</sup>)

Latest revision as of 19:10, 17 April 2024

"KHPh" redirects here. For the radio station KHPH in Hawaii, see List of radio stations in Hawaii. "KHP" redirects here. For other uses, see KHP (disambiguation).
Potassium hydrogen phthalate
Potassium hydrogen phthalate
Potassium hydrogen phthalate
Potassium hydrogen phthalate
Potassium hydrogen phthalate
Potassium hydrogen phthalate
Names
Preferred IUPAC name Potassium 2-carboxybenzoate
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
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.011.718 Edit this at Wikidata
EC Number
  • 212-889-4
PubChem CID
UNII
CompTox Dashboard (EPA)
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-1Key: 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-1Key: IWZKICVEHNUQTL-REWHXWOFAT
SMILES
  • .O=C(O)c1ccccc1C()=O
Properties
Chemical formula C8H5KO4
Molar mass 204.222 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 (pKa) 5.4
Structure
Coordination geometry tetrahedral
Hazards
Occupational safety and health (OHS/OSH):
Main hazards Irritant to eyes, skin,
and respiratory system
GHS labelling:
Pictograms GHS07: Exclamation mark
Signal word Warning
Hazard statements H315, H319, H335
Flash point Non-flammable
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkY verify (what is  ?) Infobox references
Chemical compound

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)

KHP → H 2 O {\displaystyle {\ce {->}}} K + HP

and then, acting as a weak acid, hydrogen phthalate reacts reversibly with water to give hydronium (H3O) and phthalate ions.

HP + H2O ⇌ P + H3O

KHP can be used as a buffering agent in combination with hydrochloric acid (HCl) or sodium hydroxide (NaOH). The buffering region is dependent upon the pKa, and is typically +/- 1.0 pH units of the pKa. The pKa of KHP is 5.4, so its pH buffering range would be 4.4 to 6.4; however, due to the presence of the second acidic group that bears the potassium ion, the first pKa also contributes to the buffering range well below pH 4.0, which is why KHP is a good choice for use as a reference standard for pH 4.00.

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 analysts 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

  1. "104874 | Potassium hydrogen phthalate". Archived from the original on 2014-08-21.
  2. "Lincoln Public Schools" (PDF).
  3. "C&L Inventory". echa.europa.eu.
  4. Hendrixson, W. S. (1920). "Further Work on Potassium Hydrogen Phthalate as a Standard in Volumetric Analysis". J Am Chem Soc. 42 (4): 724–727. doi:10.1021/ja01449a008.
  5. "Potassium Hydrogen Phthalate". Arlington, TX: Ricca Chemical Company. Archived from the original on 2012-11-30. Retrieved 2012-10-03.
  6. "The Standardization Of NaOH and KHP Assay" (PDF). Clark College. Archived from the original (PDF) on 2012-11-19. Retrieved 2012-10-03.
  7. 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 (1): 30–35.
  8. "pH Metrology". Projects/Programs. National Institute of Standards and Technology. Retrieved 4 August 2022.
  9. Buck, R.P.; Rondinini, S.; Baucke, F.G.K.; Brett, C.M.A.; Camoes, M.F.; Covington, A.K.; Milton, M.J.T.; Mussini, T.; Naumann, R.; Pratt, K.W.; Spitzer, P.; Wilson, G.S. (2002). "Measurement of pH. Definition, Standards, and Procedures; IUPAC Recommendation" (PDF). Pure Appl. Chem. 74: 2169–2200. doi:10.1351/pac200274112169. hdl:2434/195966. S2CID 96759529. Retrieved 4 August 2022.
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