Hydrofluoric acid
A corrosive acid used in etching, cleaning, and fluoride production.
Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. It is colorless, acidic, and highly corrosive. It is also a by-product of phosphoric acid production from apatite and fluoroapatite.
- prepared_by
- Carl Wilhelm Scheele
- common_concentration
- 49% (48–52%)
- chemical_formula
- HF in water
- primary_mineral_source
- fluorite (CaF2)
- storage_material
- fluorinated plastic (often PTFE)
Lore & Background
The acid is also recovered as a by-product during the production of phosphoric acid from apatite and fluoroapatite. Because of its high reactivity toward glass, it is stored in fluorinated plastic containers, often PTFE.
Reader's Guide
Hydrofluoric acid is a critical reagent in both laboratory and industrial settings. In industry, it is used to produce high-volume inorganic fluorides such as cryolite (Na3AlF6) and aluminium trifluoride (AlF3), which serve as solvents for metallic aluminium production. It also yields sodium fluoride and uranium hexafluoride. In the semiconductor industry, it is a major component of Wright etch and buffered oxide etch for cleaning silicon wafers. It etches glass by reacting with silicon dioxide to form gaseous or water-soluble silicon fluorides. Dilute hydrofluoric acid is used in dental restoration etching, household rust stain removers, wheel cleaners, and pre-commissioning boilers for high-pressure steam. It is also employed to dissolve rock samples and extract organic fossils from silicate rocks. Despite being a weak acid in dilute solution (pKa ≈ 3.18), concentrated solutions are highly corrosive and strongly acidic, with a Hammett acidity function comparable to that of pure sulfuric acid. Health risks are severe: it penetrates tissue, can cause delayed symptoms, and interferes with nerve function, making burns initially painless. Treatment includes calcium gluconate gel or hexafluorine.
Did You Know?
- In dilute solution, hydrogen fluoride behaves as a weak acid with pKa = 3.17, but concentrated solutions are as acidic as pure sulfuric acid.
- It is stored in fluorinated plastic (often PTFE) containers because of its high reactivity toward glass.
Frequently Asked Questions
Who is Hydrofluoric acid?
Hydrofluoric acid is a colorless, highly corrosive liquid formed when hydrogen fluoride gas dissolves in water. Fans typically encounter it as a roughly 49 % aqueous solution, with commercial concentrations falling between 48 and 52 percent.
What are Hydrofluoric acid's powers and role?
Its signature ability is dissolving glass and silica, which makes it indispensable for etching, surface cleaning, and large-scale fluoride manufacturing. It also appears as a secondary product when apatite or fluoroapatite is processed into phosphoric acid.
How does Hydrofluoric acid's story end?
Because it attacks virtually every common container material, its final chapter is spent stored in fluorinated plastics such as PTFE, where it remains stable until a chemist puts it to work. Once consumed in a reaction, it simply becomes fluoride ions dispersed in solution.
Why is Hydrofluoric acid important to the canon?
It is the go-to reagent for breaking down silicate minerals, a feat no other common acid can accomplish effectively. Without it, glass etching, semiconductor cleaning, and industrial fluoride production would all grind to a halt.
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