A carboxylic acid is an organic acid based on the carboxylate functional group, −COO−−COO−. The pKa of acetic acid, CH3COOHCH3COOH, is 4.80. The pKa of chloroacetic acid, CH2ClCOOHCH2ClCOOH, is 2.99. The pKa of trichloroacetic acid, CCl3COOHCCl3COOH, is 0.79 Acetic acid diluted in water is known as vinegar, which is safe for many food, cleaning, and alternative health applications. The other two acids are quite hazardous to our health in addition to being stronger acids, and their reactivity makes them useful as reagents in organic synthesis. Let us consider what accounts for the increased acidity and how to test those hypotheses.
Consider what trend exists in the pKapKa values for these three carboxylic acids based on their molecular formulas, then complete the following statement regarding a trend that relates to this phenomenon.
The pKa values of the carboxylic acids tend to decrease as the ___ increases.