Heat capacity of platinic acid, hydrogen hexahydroxyplatinate(IV) H2Pt(OH)(6), was measured from T = 7 K to T = 3 10 K by means of adiabatic calorimetry. The standard entropy and the standard Gibbs energy of formation of platinic acid in the crystalline state were determined to be 176.5 +/-3.6 J (.) K-1 (.) mol(-1) and -988.8 +/- 3.8 kJ (.) mol(-1), respectively.