Potassium hydrogen phthalate
From Wikipedia, the free encyclopedia
| Potassium hydrogen phthalate | |
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| 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] |
| Properties | |
| Molecular formula | KHC8H4O4 |
| Molar mass | 204.22 g/mol |
| Appearance | White or colourless solid |
| Density | 1.64 g/cm3, solid |
| Melting point |
ca. 295 °C (568 K)--decomposes |
| Solubility in water | soluble |
| Structure | |
| Coordination geometry |
tetrahedral |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | Irritant to eyes, skin, and respiratory system |
| R-phrases | R36, R37, R38 |
| Flash point | Non-flammable |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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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.[1] 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.
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.
