Potassium hydrogen phthalate
- Potassium hydrogen phthalate
Chembox new
Name = Potassium hydrogen phthalate
ImageFile = Potassium-hydrogen-phthalate-2D-skeletal.png ImageName = Potassium hydrogen phthalate
IUPACName = Potassium hydrogen phthalate
OtherNames = hydrogen potassium phthalate,phthalic acid potassium salt, potassium biphthalate, potassium acid phthalate, 1,2-benzenedicarboxylic acid,monopotassium salt,KHP, KHPh
Section1 = Chembox Identifiers
CASNo = 877-24-7
RTECS =
Section2 = Chembox Properties
Formula = KHC8H4O4
MolarMass = 204.22 g/mol
Appearance = White or colourless solid
Density = 1.64 g/cm3, solid
Solubility = soluble
MeltingPt = ca. 295 °C (568 K)--decomposes
BoilingPt =
Section3 = Chembox Structure
Coordination = tetrahedral
CrystalStruct =
Section7 = Chembox Hazards
ExternalMSDS = [http://ptcl.chem.ox.ac.uk/MSDS/PO/potassium_hydrogen_phthalate.html External MSDS]
MainHazards = Irritant to eyes, skin,
and respiratory system
FlashPt = Non-flammable
RPhrases = R36, R37, R38
SPhrases =
Potassium hydrogen phthalate, often called simply KHP, is a white or colorless, ionic solid that is the monopotassium salt of phthalic acid. The hydrogen 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, however, slightly hygroscopic and is generally kept in a desiccator before use. [ [http://www.jtbaker.com/msds/englishhtml/p5521.htm MSDS for KHP] ] 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.
In water KHP dissociates completely 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 (H3O+) and phthalate ions.
* HP- + H2O ←→ P2- + H3O+
KHP can be used as a buffering agent (in combination with HCl or 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.
ee also
* Clay theory
References
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2010.
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