Potassium and silver salts of tungstophosphoric acid (HPW) with varying amounts of the cations KxH3-xPW12O40 and AgxH3-xPW12O40 have been prepared as pure or supported on silica using the incipient wetness method. Their catalytic properties in two reactions have been studied. The vapor-phase dehydration of ethanol carried out in a conventional flow-type reactor under atmospheric pressure at temperatures varying from 398 to 773 K, and hydration of ethylene in a stainless-steel batch reactor at 478 K under the pressure of 42 atm. KxH3-xPW12O40 in the range 0 < x < 2, is composed of two phases, H3PW12O40 and K2H1PW12O40; in the range 2 less than or equal to x < 3 the solid solution is formed. Their catalytic activity in both dehydration of ethanol and hydration of ethylene decreases with increasing x, with K2H1PW12O40 and K3PW12O40 being inactive in the hydration. AgxH3-xPW12O40 forms one phase of the solid solution in the whole composition range 0 < x < 3. The catalytic activity in both reactions increases. It has been shown that catalytic activity is related to acid protons and protons generated by dissociation of water molecules coordinated by silver cations. At temperatures higher than 573 K the oxidative dehydrogenation of ethanol to acetaldehyde with high yield is observed on the AgxH3-xPW12O40 series of catalysts.