Intermediate Topic 662 of 1102 Inorganic Chemistry
Hydrofluoric Acid
A weak acid that is dangerously toxic and etches glass.
In-depth explanation of Hydrofluoric Acid
Hydrofluoric acid is an aqueous solution of hydrogen fluoride, HF, and although it is a weak acid with a pKa of about 3.2, it is extremely dangerous. Its weakness arises from the strong H-F bond and from hydrogen-bonded ion pairs. Fluoride ions bind calcium and magnesium strongly, so HF penetrates skin and deep tissue and can cause severe toxicity even from dilute solutions. It attacks glass because the Si-F bond formed is very strong: SiO2 + 4HF giving SiF4 + 2H2O. This property is used to etch glass. Calcium gluconate gel is used as an antidote for skin exposure.
Going deeper: Hydrofluoric Acid
Key ideas: HF is weak in dilute solution (pKa 3.2) but forms strongly bonded F- with HF2- (bifluoride), so concentrated acid is stronger. It dissolves glass: SiO2 + 4HF gives SiF4 + 2H2O, used for etching, so keep in plastic (polyethylene, Teflon). Toxic through skin because F- binds Ca2+ and Mg2+ and causes hypocalcemia, treated with calcium gluconate gel. Used to make Teflon, refrigerants, UF6.
Common mistakes and connections: Students assume weak acids are safe; HF is among the most dangerous, since it penetrates tissue painlessly at first. Do not store in glass. HF is a weak acid because of the strong H-F bond and high hydration enthalpy of F-, not because it is poorly soluble. Links to hydrogen bonding, equilibrium and enrichment chemistry.
Visualization of Hydrofluoric Acid
Titration of a weak acid with pKa 3.2 like HF: it is only partly ionized, yet the fluoride and HF remain dangerous. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Hydrofluoric acid etches the surface of a glass container, leaving a frosted pattern.
Frequently asked questions about Hydrofluoric Acid
What is Hydrofluoric Acid?
A weak acid that is dangerously toxic and etches glass.
Is Hydrofluoric Acid a beginner, intermediate or advanced topic?
Hydrofluoric Acid is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Hydrofluoric Acid?
Study these earlier topics in Inorganic Chemistry first: Halogens, Halogen Reactivity Trend, Hydrogen Halides.
What comes after Hydrofluoric Acid?
The next topics in Inorganic Chemistry are Interhalogen Compounds and Oxoacids of Chlorine.
Can I practise Hydrofluoric Acid with quizzes?
Yes. The interactive lesson includes a self-check question on Hydrofluoric Acid, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Hydrofluoric Acid fits in Inorganic Chemistry
Hydrofluoric Acid is topic 47 of 113 in Inorganic Chemistry.