Thermochemistry of Sodium Tungstate, Silver Tungstate and Tungstic Acid

The heat of solution of Na₂WO₄ has been measured and the standard heat of solution calculated to be -1.6 kcal/mole. Because this heat of solution is very differnent from that calculated from previously reported heats of formation, Robert L. Graham and Loren G Hepler have measured the heat of reaction of crystalline tungstic acid(H₂WO₄) with excess aqueous sodium hydroxide and have found the standard heat of solution of AgNO₃ in water have been measured and the standard heats found to be -12.39,-8.12 and 5.42 kcal/mole, respectively. The heats of reaction and solution have been used to calculate the heats of formation of WO₄^-(aq), Na₂WO₄(c) and Ag₂WO₄(c) to be -266.6，-379.6 and -230.7 kcal/mole, respectively. The thermodynamics of solution of Ag₂WO₄ is discussed in terms of polytungstate formation.


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