Potassium hydrogen phthalate

Structural formula
General
Surname	Potassium hydrogen phthalate
other names	Potassium acid phthalate 1,2-benzenedicarboxylic acid, monopotassium salt
Molecular formula	C 8 H 5 KO 4
Brief description	white solid
External identifiers / databases
CAS number 877-24-7 EC number 212-889-4 ECHA InfoCard 100,011,718 PubChem 23676735 ChemSpider 12839 Wikidata Q424699
properties
Molar mass	204.22 g mol −1
Physical state	firmly
density	1.64 g cm −3
Melting point	295–300 ° C (decomposition)
solubility	moderate in water (80 g l −1 at 20 ° C) moderately in ethanol
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	> 3200 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium hydrogen phthalate (also called potassium acid phthalate) is a salt of o -phthalic acid . The colorless, crystalline solid is soluble in water.

properties

In water dissociates potassium hydrogen phthalate completely to form a potassium - cation (K ⁺ ) and a Hydrogenphthalat- anion (H P ^- ). As a weak acid, hydrogen phthalate reacts reversibly to a small extent with water to form oxonium (H ₃ O ⁺ ) and a doubly negatively charged phthalate ion (P ²⁻ ).

${\displaystyle \mathrm {H{\mathit {P}}^{-}+\ H_{2}O\ \rightleftharpoons \ {\mathit {P}}^{2-}+\ H_{3}O^{+}} }$

use

Potassium hydrogen phthalate is used as a standard reference material for pH measurement (pH 4.01) and as a buffer substance (in combination with hydrochloric acid or sodium hydroxide ). It is also used as a concentration standard for measurements of organically bound carbon (TOC) and related sum parameters of the organic pollution of water.

See also

• Primary substance
• Secondary standard
• Customized solution

Individual evidence

1. ↑ ^{a b c} data sheet potassium hydrogen phthalate (PDF) from Carl Roth , accessed on August 24, 2017.
2. ↑ ^{a b c} data sheet Potassium hydrogen phthalate from Sigma-Aldrich , accessed on August 24, 2017 ( PDF ).
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 89th edition. (Internet version: 2009), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-438.
4. ↑ Data sheet pH buffer solution pH 4.01 (PDF) from Carl Roth , accessed on December 14, 2010.