Question

The $H{{F}_{2}}^{-}$ion exists in the solid-state and also in liquid ${H}{F}$ solution, but not in dilute aqueous solution.
If true enter 1, else enter 0.

Answer 1

Hint: Hydrogen fluoride is an ionic compound. However, the shared pair of electrons is attracted by the fluorine atom due to high electronegativity. Due to this Hydrogen atom obtains a partial positive charge and forms a weak bond with the next fluorine atom. This is the reason why HF when dissolved in water reacts differently.

Complete step-by-step answer:
Hydrogen fluoride is colourless gas or liquid which is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid.
It is an important reactant in the preparation of many important compounds in pharmaceuticals as well as in the preparation of polymers like Teflon. HF is widely used in the petrochemical industry as a component of superacid.
Hydrogen fluoride boils near room temperature, which is much higher than other hydrogen halides. This is because HF molecules form strong intermolecular hydrogen bonds and do not bond with the water molecules.
Hydrogen fluoride molecules exist as $H{{F}_{2}}^{-}$ ion in the crystal lattice. In liquid form hydrogen molecules exist as $H{{F}_{2}}^{-}$ions releasing ${{H}^{+}}$ions in the liquid. The reaction is shown below:
\[\rightleftharpoons 2\text{HF }\overset{{}}{leftrightarrows}\text{ H}{{\text{F}}_{2}}^{-}\text{ + }{{\text{H}}^{+}}\]$$
However, in aqueous solution, the intermolecular hydrogen bonding in HF molecules is prevalent than the hydrogen bond formation with water molecules and the dissociation happens differently. The reaction is shown below:
$\text{HF + }{{\text{H}}_{2}}\text{O }\overset{{}}{leftrightarrows}\text{ }{{\text{H}}_{3}}{{\text{O}}^{+}}\text{ + }{{\text{F}}^{-}}$
Hence in aqueous solution, hydrogen fluoride does not exist as $H{{F}_{2}}^{-}$ ion.

Therefore, the statement: The $H{{F}_{2}}^{-}$ion exists in the solid-state and also in liquid HF solution, but not in dilute aqueous solution is true and the answer to the question is 1.

Note: Hydrogen fluoride is used in refrigerants, herbicides, pharmaceuticals, aluminium, electrical components etc. However, exposure to hydrogen fluoride gas has some serious health issues. Upon contact with moisture(including tissue), it converts into highly corrosive hydrofluoric acid. It can also cause blindness and destruction of the cornea.