Science Fair Project Encyclopedia
Hydrofluoric acid
| General | |
|---|---|
| Name | Hydrogen fluoride |
| Chemical formula | HF |
| Appearance | Colorless gas |
| Physical properties | |
| Formula weight | 20.1 amu |
| Melting point | 190 K (-83 °C) |
| Boiling point | 294 K (19.5 °C) |
| Density | 0.97 ×10³ kg/m³ (liquid) |
| Solubility | miscible with water |
| Thermochemistry | |
| ΔfH0gas | ? kJ/mol |
| ΔfH0liquid | ? kJ/mol |
| ΔfH0solid | ? kJ/mol |
| S0gas, 1 bar | ? J/mol·K |
| S0liquid, 1 bar | ? J/mol·K< |
| S0solid | ? J/mol·K |
| Safety | |
| Ingestion | Toxic, most likely fatal. |
| Inhalation | Extraordinarily toxic, most likely fatal in concentrations >200ppm, non-fatal doses can result in pulmonary edema. |
| Skin | Absorbs through skin to cause nerve, bone and organ damage. The affected area may have to be cut away to prevent the acid spreading. Can be fatal. |
| Eyes | Extremely dangerous, high chance of blindness. |
| SI units were used where possible. Unless otherwise stated, standard conditions were used. | |
Hydrofluoric acid is a highly corrosive solution of the chemical compound hydrogen fluoride in water. Pure hydrogen fluoride is often called anhydrous hydrofluoric acid. Paradoxically, though in chemical terms hydrofluoric acid is a weak acid. This is because it does not dissociate completely in water due to the relatively high strength of hydrogen-fluorine bonds. Hydrofluoric acid is notoriously known to react with glass (SiO2):
- SiO2(s) + 6 HF(aq) → H2[SiF6](aq) + 2 H2O(l)
Consequently, it must be stored in plastic containers, though ideally it should be stored in Teflon bottles. It also has the unique ability to dissolve almost all inorganic oxides. In the human body, hydrofluoric acid reacts with calcium and damages nerves, bone, and several organs including the heart and kidneys.
Initial treatment to hydrofluoric acid exposure usually involves applying calcium gluconate gel to the exposed areas. If exposure is high, or too much time has passed, a calcium solution may be injected directly into a local artery or surrounding tissues. In all cases, hydrofluoric acid exposure requires immediate professional medical attention.
Production
Industrially, hydrofluoric acid is produced from the mineral fluorspar, also known as calcium fluoride (chemical formula CaF2) and concentrated sulfuric acid. When combined at 250°C, these two substances react to produce hydrogen fluoride according to the chemical equation
- CaF2 + H2SO4 → 2 HF + CaSO4
The vapors from this reaction are a mixture of hydrogen fluoride, sulfuric acid, and a few minor byproducts, from which hydrogen fluoride can be isolated by distillation.
Uses
Hydrofluoric acid's ability to dissolve oxides makes it important in the purification of both aluminium and uranium. It is also used to etch glass, to remove surface oxides from silicon in the semiconductor industry, as a catalyst for the alkylation of iso-butane and butene in oil refineries and to remove oxide impurities from stainless steel in a process called pickling.
Hydrofluoric acid is also used in the synthesis of many fluorine-containing organic compounds, including teflon and refrigerants such as freon.
Safety
In the body, hydrofluoric acid reacts with calcium and magnesium ions and can disable organs whose proper function depends on these metal ions. Exposure to hydrofluoric acid may not be initially painful, and symptoms may not occur until several hours later, when the acid begins to react with calcium in the bones. If left untreated, hydrofluoric acid exposure can result in severe or even lethal damage to the heart, liver, kidneys, and nerves.
Exposure of less than 10% of the body can be fatal, even with immediate medical treatment. Highly concentrated solutions may be fatal in at least 2% body exposure[1]
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