Hydrofluoric acid is an aqueous solution of hydrogen fluoride gas, which is a clear, colorless, smoky and corrosive liquid with a strong pungent smell. Melting point -83.3℃, boiling point 19.54℃, flash point 1 12.2℃, density 1 150kg/m? . Soluble in water and ethanol, slightly soluble in ether. It is a weak acid.

Hydrofluoric acid is a weak acid, because hydrogen atoms and fluorine atoms have strong binding ability in aqueous solution, and hydrogen bonds exist between hydrogen fluoride molecules, so hydrofluoric acid cannot be completely ionized in water. Extremely corrosive, it can strongly corrode metals (metals prior to hydrogen), glass and silicon-containing objects. Inhalation of steam or contact with skin can cause incurable burns. Laboratories are generally made of fluorite (mainly calcium fluoride) and concentrated sulfuric acid, which need to be sealed in plastic bottles and kept in a cool place.

Hydrofluoric acid is a weak acid, which is partially ionized into hydrogen ions and fluorine ions. Strong corrosiveness, serious damage to teeth and bones. It is very corrosive to silicon compounds. It should be kept in a closed plastic bottle.

Hydrofluoric acid is a mixture obtained by dissolving hydrogen fluoride in water, which is used for carving glass, cleaning residual sand on castings, controlling fermentation, electropolishing and cleaning corroded semiconductor silicon wafers (mixed acid plus nitric acid). Hydrofluoric acid can not be completely ionized in water, because the binding ability between hydrogen atoms and fluorine atoms is relatively strong.

Hydrofluoric acid can dissolve many glasses (main component: silicon dioxide) that other acids cannot dissolve, and the reaction equation for generating gaseous silicon tetrafluoride is as follows:

SiO 2(s)+4HF(AQ)= = si F4(g)↑+ 2H2O(l)

The generated SiF4 can continue to react with excess HF to generate fluosilicic acid;

si F4(g)+2HF(AQ)= = H2[si F6](AQ)

Fluorosilicic acid is a binary strong acid.

For this reason, it must be kept in plastic (theoretically, it is best to put it in a container made of PTFE), wax or lead. Hydrofluoric acid has no reducibility. If it is to be stored for a long time, it is necessary not only to seal the container, but also to exhaust the air in the container as much as possible.

It reacts with silicon and silicon compounds to produce gaseous silicon tetrafluoride (which can corrode glass), but has no corrosive effect on plastics, paraffin, lead, gold and platinum. It is miscible with water and ethanol. The mass fraction of commercially available hydrofluoric acid solute is 40%, equivalent to 22.5 mol/L, and 35.35% hydrofluoric acid is a * * * boiling mixture. Highly toxic, the minimum lethal dose (rat, abdominal cavity) is 25mg/kg. Corrosive, can strongly corrode metal, glass and silicon-containing objects. Such as inhalation of steam or contact with the skin can form an ulcer that is difficult to heal.

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