The osmotic and activity coefficients of CF3COONa(aq) and CF3COOK(aq) have been determined at the temperature T = 298.15 K by the isopiestic method in the molality range from 0.2 mol . kg(-1) to the molalities (47.1 and 58.3) mol . kg(-1), respectively. The results have been analyzed in terms of ion-ion and ion-water interactions and compared with the literature for aqueous CH3COONa, CCl3OONa, and simple inorganic 1-1 salts. The discussion confirmed our hypothesis that the main factor which determines the influence of the 1-1 salts on water activity is the size of the ions. We did not observe any specific influence of hydrophobic groups on the state of water in solution.