# Five solutions were prepared by dissolving 0.00100 mole of each of the following compounds in enough water to make 1.000 liter of solution. Which one of these compounds would make the most acidic solution? Why?

## $C {O}_{2}$ ${P}_{4} {O}_{6}$ ${P}_{4} {O}_{10}$ $S {O}_{2}$ $S {O}_{3}$

Take an oxo acid, sulfuric acid, nitric acid, phosphoric acid, take away the elements of water, and you form the so-called $\text{acid anhydride}$, literally the acid sans water.
Add the elements of water, you get back the acid. Clearly, sulfur trioxide is the acid anhydride of sulfuric acid, ${H}_{2} S {O}_{4}$, which would be the strongest acid available, so strong that dissociation to sulfate ion would be almost quantitative .