Rank the following acids in decreasing (strongest to weakest) order of acidity.
A) V III I II IV
B) II I III V IV
C) IV III I II V
D) IV V III I II
E) V I III II IV

Question

Rank the following acids in decreasing (strongest to weakest) order of acidity.  
A) V > III > I > II > IV 
B) II > I > III > V > IV 
C) IV > III > I > II > V 
D) IV > V > III > I > II 
E) V > I > III > II > IV

Quizplus · Accepted Answer

The strength of an acid depends on its ability to donate a proton (H+). The more stable the resulting ion after donating a proton, the stronger the acid. In option B, II is the strongest as it has a stable anion after donating a proton. I is the next strongest as the negative charge is delocalized over two oxygen atoms, followed by III which has the negative charge localized on one oxygen atom. V is the weakest as the negative charge is stabilized by an electron-withdrawing phenyl (benzene) group, making it difficult for the acid to donate a proton. IV is intermediate in strength since the anion is resonance stabilized but one of the oxygen atoms is bound to sulfur, which is less electronegative than the oxygen atoms in I and II.

Rank the Following Acids in Decreasing (Strongest to Weakest) Order