Question

Sodium sulfate is soluble in water, whereas barium sulfate is sparingly soluble because:
A. hydration energy of sodium sulfate is more than its lattice energy.
B. lattice energy of barium sulfate is more than its hydration energy.
C. lattice energy has no role to play in solubility.
D. hydration energy of sodium sulfate is less than its lattice energy.

Answer 1

Hint : Hydration energy of any solution should exceed lattice energy. Lattice energy is always negative since energy is released when bonds are formed. It denotes the strength of ionic bonds. Lower the energy, higher the stability.

Complete step by step solution :
Ionic compounds are formed if one of the species of electrons is electron rich and other is electron deficient. The factors which influence the ionic bond formation are-ionization energy, lattice energy, and electron affinity. Lattice energy is the energy change when one mole of solid ion crystal is formed from its constituent gaseous ions. Higher the lattice energy, stronger the ionic bond. Charge and radius of the ions are the factors influencing the lattice energy. When the charge on the ion is high, then lattice energy is high. Larger ions have low lattice energy.
Hydration energy is the energy used to break one mole of ionic crystal to its constituent water molecule.
For an ionic compound to be soluble, its lattice energy should be less than its hydration energy. Therefore sodium sulfate is soluble in water because hydration energy of sodium sulfate is more than its lattice energy. Barium sulfate is sparingly soluble because its lattice energy is more than its hydration energy.

Additional information:
Ions of higher charge have strong interaction towards each other. Therefore more energy is released when bonds are formed. For larger ions, interaction between ions gets reduced as the distance between them increases. So less energy is released when bonds are formed.

Note : Lattice energy is inversely proportional to the sum of radii. Hydration energy is the sum of two quantities inversely proportional to individual radii. Hydration energy is influenced by the ionic radii of cation and anion.