Heat capacity density of the acid solution

Question

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:

H₃O+(aq) + NaCH₃CO₂ · 3 H₂O(s)

→Na+(aq) + CH₃COOH(aq) + 4 H₂O(l).

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.