Why does vinegar taste sour

The German chemist Liebig, in 1838, was the first to suggest mobile, replaceable, hydrogen atoms being responsible for acidic properties. Arrhenius extended the idea in 1887, when he said the hydrogen existed as a proton. 

The O-H bond in an acid is sometimes said to be labile, since it is so easily broken. The word derives from the Latin labi, to lapse (i.e. to change). 

The Lowry-Bronsted theory says an acid is a proton donor. 

We say the acid dissociates. The bare proton is very small, and has a large charge density, causing it to attract the negative end of the water dipole. The proton produced by Equation (6.1) is, therefore, hydrated in aqueous solutions, and is more accurately represented by saying H+(aq). 

We see how solvated protons impart the subjective impression of a sour, bitter flavour to the ethanoic acid in vinegar. In fact, not only the sour flavour, but also the majority of the properties we typically associate with an acid (see Table 6.1) can be attributed to an acidic material forming one or more solvated protons H+(aq) in solution. 

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