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Element Index
Hafnium
Holmium
Hydrogen
Nitrogen
Chemical's truth
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Ricin is a natural poison extracted from the castor oil bean with a quoted LD50 of 20,000 ng/kg. |
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Hydrogen fluoride
(anhydrous hydrofluoric acid)
CAS no: 7664-39-3 Formula: HF Molecular weight: 20.006
Physical Data
Appearance: Colorless, highly corrosive gas.
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Melting point: -83.35°C
Boiling point: 19.5°C
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Density: 0.818 g/L
Solubility: very soluble
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Thermodynamic Data (gas phase)
Enthalpy of formation: -273.3 kJ/mol
Gibbs energy of formation: -275.4 kJ/mol
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Entropy: 173.8 J/mol K
Heat capacity: -
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Production and preparation
Can be obtained by the action of concentrated sulfuric acid on fluorspar (> 98% CaF2). The reaction is endothermic and heat is supplied to obtain
good yields.
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Anhydrous HF can be obtained by fractional distillation in steel vessels. The technical requirements to enable the safe manufacture and handling of the substance are considerable. It is usually packaged in steel cylinders or polyethylene-lined
drums holding.
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Behavior and Chemical Properties
Hydrogen fluoride fumes in moist air and is very soluble in water and alcohol but only slightly soluble in ether. Anhydrous HF is one of the most acidic substance known. But in
aqueous solution (hydrofloric acid) it is a weak acid, due to extensive hydrogen bonding among the HF molecules. This also accounts for relatively high boiling point and melting
point when compare with other hydrogen halides.
HF attacks silica that contains in glass and concrete:
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History and Uses
With potassium hydrogen floride, HF is used as electrolyte to produce fluorine gas (Moissan process). HF is also used as fluorinating agents in the aluminium industry (synthetic cryolite) and
nuclear industry (UF4 and UF6), and in chemical industry for manufacture of fluoride salts.
In organic industry, HF fluorinates chloroform to give chlorodifluoromethane. The latter substance is used to make an important synthetic resin, tetrafluoroethylene of more famously known by
its trade name of TEFLON.
HF is also used as glass etching, rocket propellant stabilizers, microelectronic circuits and stain removers.
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Hazard, Storage and Handling
HF is highly irritating, corrosive and poisonous. It should be stored in steel cylinder but not in glassware as HF attacks silica (in glass). Must be separated from
incompatible substances such as cast iron, certain metals and alloys, concrete, alkalis and organic materials (wood, natural rubber, leather etc). Contact with incompatible substances may generate hazardous gas
such as hydrogen.
Can cause severe damage in all routes of exposure: acute corrosive to skin, eyes, mucous membrane and even result in death. Even when clothings are contaminated with small
amount of HF (concentrated or diluted) can result in serious delay effects such as painful skin-ulcers and progressive tissue damage. Quite often the dilute form show no effect for the first few hours.
Area of work must be well ventilated, appropriate acid-resistant protective gear must be worn, such as neoprene gloves, googles, face shields, apron. All protecting clothing must be
washed after each use.
Note: first aid and medical treatment for HF is very specific and critical. Inform medical health officers about HF exposure before sending
the victim to the hospital. Any spillage or exposure, confirmed or suspected, must be treated immediately. Seek immediate medical attention even if the exposure is slight. If come into skin and eye contacts, splash with plenty of water for at least 15 minutes and contaminated clothing must be remove
while flushing. If available, apply calcium gluconate gel to treat burns. Upon ingestion, drink plenty of water and do not induce vomit. After that some milk can be given to soothe the burning effect.
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(Last update: February 2003) |
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