Ethyne, commonly known as acetylene, is an alkyne hydrocarbon with the chemical formula C2H2. Unlike most other alkenes and alkynes, ethyne is not very soluble in water. Its solubility in water at 25 °C is only 1.3 mL/L. This is because ethyne is a nonpolar molecule, while water is a polar molecule. Nonpolar molecules are repelled by water molecules, while polar molecules are attracted to water molecules.

The relatively low solubility of ethyne in water allows it to be collected by water displacement. This means that ethyne can be collected by bubbling it through a container of water. The ethyne will rise to the top of the container and can be collected by placing a collection vessel over the top of the container.

Water displacement is a common method for collecting gases that are not very soluble in water. Other gases that can be collected by water displacement include methane, ethene, and propane.