Question

What is the heat of hydration for the reaction between magnesium sulfate heptahydrate (MgSO4•7H2O) and water (H2O) when 3.50 g of MgSO4•7H2O is dissolved in 50.0 mL of water at 25 °C? The molar heat of hydration for MgSO4•7H2O is –90.39 kJ/mol.

Answer 1

To calculate the heat of hydration for the reaction, we first need to determine the number of moles of MgSO47H2O that are present in the 3.50 g sample. The molar mass of MgSO47H2O is:Mg = 24.31 g/molS = 32.07 g/molO4 = 4  16.00 g/mol = 64.00 g/mol7H2O = 7   2  1.01 g/mol + 16.00 g/mol  = 7  18.02 g/mol = 126.14 g/molMolar mass of MgSO47H2O = 24.31 + 32.07 + 64.00 + 126.14 = 246.52 g/molNow, we can calculate the number of moles of MgSO47H2O in the 3.50 g sample:moles = mass / molar mass = 3.50 g / 246.52 g/mol = 0.0142 molNext, we can use the molar heat of hydration to determine the heat released when these moles of MgSO47H2O are dissolved in water:heat of hydration = moles  molar heat of hydration = 0.0142 mol   -90.39 kJ/mol  = -1.283 kJTherefore, the heat of hydration for the reaction between 3.50 g of MgSO47H2O and water at 25 C is -1.283 kJ.