## Chemistry: The Central Science (13th Edition)

$H_2C_2O_4$ is stronger than $HC_2{O_4}^-$ because, it is easier to take a proton from a neutral compound than from an anion. And they don't have other difference (besides the hydrogen)
This happens because, since the proton $(H^+)$ is positive, it is attracted by the anion, which complicates the donation, decreasing the acidity.