Hydrofluoric Acid (HF): Properties, Uses, Storage & Effect On Skin

Overview

Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water and is a precursor to almost all fluorine-containing compounds. It is a colorless solution that is highly corrosive, capable of dissolving many materials especially oxides. Hydrogen fluoride also shows moderate reactivity toward many metals and has the ability to dissolve glass. Due to its moderate reactivity toward many metals and high reactivity towards glass, hydrofluoric acid is usually stored in plastic containers.

Hydrofluoric acid is mainly used for semiconductor and electronic fabrication, mineral processing and glass etching. In addition to its useful properties, hydrofluoric acid also poses severe health risk upon exposure.

Physical And Chemical Properties

The exact physical and chemical properties of hydrofluoric acid (boiling point, melting point, density and reactivity) depend on the concentration of hydrogen fluoride in the aqueous solution. The physical and chemical properties include:

• Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water.
• Hydrofluoric acid is a colorless fuming gas
• The molar mass of hydrofluoric acid is 20.0063g/mol
• Hydrofluoric acid is a gas at temperatures above 19.5^oC
• The boiling point of hydrofluoric acid is -83.55^oC
• It has a density of 1.15g/cm³
• Hydrofluoric acid is a very strong and highly corrosive.
• Hydrofluoric acid readily reacts with bases, acids and oxidants
• The acid has a dissolving effect on glass and ceramics.
• The acidity of hydrofluoric acid solutions varies with concentration owing to hydrogen-bond interactions of the fluoride ion.

Preparation

Hydrofluoric acid is prepared industrially by treatment of mineral fluorite (CaF₂) with concentrated sulphuric acid at a high temperature (256^oC). This reaction produces hydrogen fluoride and calcium sulphate.

CaF_2(s) +H2SO_{4 (aq)}―> 2 HF_(g) +CaSO_{4 (S)}

The hydrogen fluoride is eventually dissolved in water to yield the hydrofluoric acid, in the required concentrations.

Storage

Store hydrofluoric acid in a cool dry place away from incompatible materials. Hydrofluoric acid reacts with many materials therefore avoid contact with glass, concrete, metals, water, other acids, oxidizers, reducers, alkalis, combustibles, organics and ceramics.

Store in containers made of polyethylene or fluorocarbon plastic, lead or platinum. Place storage bottles in polyethylene secondary containment trays.

Uses

• It is used in the semiconductor industry to clean silicon wafers.
• It is also used for many industrial purposes such as glass etching, metal cleaning and rust removal
• It is widely used in the preparation of many useful fluorine compounds such as Teflon (PTFE plastic), Freon (refrigerant), fluorocarbons and many medications such as fluoxetine (Prozac).
• It is used in preparation of inorganic fluorides such as sodium fluoride, uranium hexafluoride, aluminum trifluoride etc.
• Hydrofluoric acid is useful to dissolve rock samples (generally powdered) because of its ability to dissolve most of the silicates and the oxides.
• It is used to polish and frost glass.
• It is used in preparation of a catalyst used in oil refinery process referred to as alkylation.
• In metalworking, it acts as a pickling agent to remove oxides and other impurities from carbon steels and stainless steel.

Hazards Associated With Hydrofluoric Acid

• Upon exposure, hydrofluoric acid is similar to other acids in that the initial extent of a burn depends on the concentration, the temperature and the duration of contact with the acid.
• Hydrofluoric acid (HF) differs from other acids because the fluoride ion readily penetrates the skin, causing destruction of deep tissue layers, including bone.
• Hydrofluoric acid and hydrogen fluoride vapor can cause severe burns to the eyes, which may lead to permanent damage and blindness.
• Ingestion may result in vomiting and abdominal pain
• Inhalation of hydrofluoric acid vapor may cause severe throat irritation, cough, dyspnea and pulmonary edema resulting in death.

Summary Of  What You Need To Know Hydrofluoric Acid In Tabular Form