|Molar mass||58.0967 g/mol (anhydrous)
94.1273 g/mol (dihydrate)
|Melting point||858 °C (1,576 °F; 1,131 K) (anhydrous)
41 °C (dihydrate)
19.3 °C (trihydrate)
|Boiling point||1,502 °C (2,736 °F; 1,775 K)|
92 g/100 mL (18 °C)
102 g/100 mL (25 °C)
349.3 g/100 mL (18 °C)
|Solubility||soluble in HF
insoluble in alcohol
|EU classification||Toxic (T)|
|S-phrases||(S1/2), S26, S45|
LD50 (Median lethal dose)
|245 mg/kg (oral, rat)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide and occurs naturally as the rare mineral carobbiite. Aqueous solutions of KF will etch glass due to the formation of soluble fluorosilicates, although HF is more effective.
Potassium fluoride is prepared by dissolving potassium carbonate in excess hydrofluoric acid. Evaporation of the solution forms crystals of potassium bifluoride. The bifluoride on heating yields potassium fluoride:
- K2CO3 + 4HF → 2KHF2 + CO2↑ + H2O
- KHF2 → KF + HF↑
The salt must not be prepared in glass or porcelain vessels as HF and the aqueous solution of KF corrode glass and porcelain. Heat resistant plastic or platinum containers may be used.
Applications in organic chemistry
In organic chemistry, KF can be used for the conversion of chlorocarbons into fluorocarbons, via the Finkelstein reaction. Such reactions usually employ polar solvents such as dimethyl formamide, ethylene glycol, and dimethyl sulfoxide.
Like other sources of the fluoride ion, F−, KF is poisonous, although lethal doses approach gram levels for humans. It is harmful by inhalation and ingestion. It is highly corrosive, and skin contact may cause severe burns.
- Vogel, A. I.; Leicester, J.; Macey, W. A. T. "n-Hexyl Fluoride". Org. Synth.; Coll. Vol. 4, p. 525
- Han, Q.; Li, H-Y. "Potassium Fluoride" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons,New York. doi:10.1002/047084289X.rp214
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