1.Hydrogen fluoride , HF exists as liquid at room emperature . Explain this phenomenon based on the formation of hydrogen bonds .
2.Explain why paper sticks together when wet.
(1) Hydrogen fluoride easily creates hydrogen bonds between molecules, which increases HF’s boiling point to 19°C(66.2°F); far above the boiling points of the other hydrogen halides, highest of which is hydrogen iodide at -35°C(-31°F). Fluorine being highly electronegative and as the size of fluorine atom is small, hence it forms intermolecular hydrogen bonding. If ambient temperature rises by just a few degrees HF should start boiling. Although, HF becomes Hydrofluoric acid when it comes into contact with moisture. The easy hydrogen bonding and quick hydration may prevent any visible boiling to occur.
(2) The paper fibres of wet paper absorb water molecules, which cling to each other like weak glue. The water molecules are held together by cohesive forces, as they are polar and produce hydrogen bindings to their closest neighbours.