Final answer:
The lower pKa of CF3CO2H compared to CH3CO2H is due to the electron-withdrawing effects of the trifluoromethyl group in CF3CO2H, which stabilizes the conjugate base and makes the acid stronger.
Step-by-step explanation:
The difference in pKa values for CH3CO2H (acetic acid) and CF3CO2H (trifluoroacetic acid), which are 4.75 and 0.23 respectively, can be attributed to the electron-withdrawing effects of the substituents attached to the carboxylic acid group. In the case of acetic acid, the methyl group has a slight electron-donating effect, which makes the carboxylic acid proton (H) slightly less acidic. Conversely, the trifluoromethyl group in trifluoroacetic acid strongly pulls electron density away from the carboxyl group due to the high electronegativity of fluorine. This increased electron withdrawal stabilizes the conjugate base, resulting in a lower pKa and a stronger acid.
It is also noteworthy that the pKa values are generally independent of temperature because these specific measurements are less sensitive to temperature changes. However, autoionization constants like Kw do change with temperature, affecting the pH of water but not necessarily the pKa of these acids directly.