Without looking them up, rank the following compounds in decreasing order of acidity. These examples represent large classes of compounds that differ widely in acidity.
water, ethanol, 2-chloroethanol, tert-butyl alcohol, ammonia, sulfuric acid, hexane, hex-1-yne, acetic acid

Acidity refers to the ability of a compound to donate a proton (H+) in a chemical reaction. The strength of an acid is often measured by its pKa value, where lower pKa values indicate stronger acids. Understanding the pKa helps in ranking compounds based on their acidity, as it provides a quantitative measure of how readily a compound can release a proton.

Different functional groups in organic compounds significantly affect their acidity. For instance, carboxylic acids (like acetic acid) are generally more acidic than alcohols due to the resonance stabilization of their conjugate bases. Halogen substituents, such as in 2-chloroethanol, can also enhance acidity through inductive effects, making the compound more likely to donate a proton.

Certain common compounds have well-established acidity rankings. For example, strong acids like sulfuric acid are much more acidic than alcohols or amines. Water is more acidic than alcohols, while hydrocarbons like hexane are considered neutral. Familiarity with these comparative acidities is essential for accurately ranking the given compounds.