When 1.3584 g of sodium acetate trihydrate was mixed into 100.0 cm³ of 0.2000 m HCl(aq) at 25°C in a solution calorimeter, its temperature fell by 0.397°C on account of the reaction:

The heat capacity of the calorimeter is 91.0 J K⁻¹ and the heat capacity density of the acid solution is 4.144 J K⁻¹ cm⁻³. Determine the standard enthalpy of formation of the aqueous sodium cation. The standard enthalpy of formation of sodium acetate trihydrate is −1064 kJ mol⁻¹.

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H3O+ (aq) + NaCH3CO₂. 3 H₂O(s) → Na+ (aq) + CH3COOH(aq) + 4H₂O(1).