Both HCOOH and CH3COOH are weak acids. CH3COOH is a slightly weaker acid than HCOOH. The strengths of carboxylic acids vary with the total electron-withdrawing power of the atoms bonded to the carboxyl group. The more electron-withdrawing the substituent group, the stronger the acid. The CH3 group is less electron-withdrawing than H and we expect that CH3COOH is a weaker acid than HCOOH