The second dissociation constant of sulfuric acid is determined in 1M
NaClO4 at 25-degrees-C using an electrochemical cell without liquid ju
nction consisting of a glass and a perchlorate electrode. By taking in
to account the association between the Na+ and SO42- ions an average v
alue of 0.0184+/-0.0005 is found using three different methods. This c
orresponds with an apparent acidity constant K(A2) of 0.095 +/-0.003