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

Question

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

Quizplus · Accepted Answer

The strength of an acid depends on its ability to donate a proton (H+ ion). The more stable the conjugate base of an acid, the stronger the acid. In other words, the more easily the conjugate base can accept a proton, the stronger the acid. With this in mind, we can look at the following acids and their corresponding conjugate bases:

I. HClO4 (conjugate base: ClO4-) - Very strong acid with a weakly stable conjugate base
II. CH3COOH (conjugate base: CH3COO-) - Weak acid with a stable conjugate base
III. HNO2 (conjugate base: NO2-) - Weak acid with a stable conjugate base
IV. H2SO4 (conjugate base: HSO4-) - Very strong acid with a weakly stable conjugate base
V. H3PO4 (conjugate base: H2PO4-) - Moderately strong acid with a moderately stable conjugate base

Based on this analysis, we can see that the correct order of decreasing acidity is: I > IV > V > II > III. This matches with answer choice D.

Rank the Following Acids in Order of Decreasing Acidity