Question

Which one of the following alkaline earth metal sulphates has its hydration enthalpy greater than its lattice enthalpy?
A. $CaS{{O}_{4}}$
B. $BeS{{O}_{4}}$
C. $BaS{{O}_{4}}$
D. $SrS{{O}_{4}}$

Answer 1

Hint: The amount of energy required to convert one mole of an ionic solid into gaseous state is called lattice energy. Lattice energy is also called ionization energy.
The amount of energy released when one moles of an ion undergoes hydration is called hydration energy.

Complete step by step answer:
- All the metal sulphates given in the options of the question belong to alkaline earth metals meaning group II A elements.
- The group II A elements are Beryllium, Magnesium, Calcium, Strontium, Barium, Radium.
 - As moving from top to bottom in the periodic table the solubility of the alkaline sulphates decreases. Means sulphates of barium and radium are insoluble in water.
- Then among the given options Barium sulphate ($BaS{{O}_{4}}$ ) has less hydration energy or less hydration enthalpy among the given options.
- Beryllium sulphate ($BeS{{O}_{4}}$ ) has high solubility in water means beryllium sulphate has high hydration energy among the given options.
 - Now coming to lattice enthalpy of lattice energy, as we are moving from top to bottom in the periodic table the size of the atom increases means Beryllium has low atomic size.
- So, because of less atomic size Beryllium sulphate breaks easily and has less lattice enthalpy.
- Therefore Beryllium sulphate has high hydration and less lattice energy among the given options.
So, the correct answer is “Option B”.

Note: Hydration energy and lattice energy are inversely proportional to each other. As the hydration energy of the molecule is high then lattice energy will be low and vice versa. The trend is applicable to all the atoms present in the periodic table.