Question

For two ionic compounds XY and AB, the data of their lattice energy and hydration energy is given as:
$\begin{array}{ccc}\text{Compound}& \text{Lattice energy (kJ/mol)}& \text{Hydration energy(kJ/mol)}\\ XY& 400& 1000\\ AB& 600& 2000\end{array}$
What will be the correct order of solubility in water?

• A. AB > XY
• B. XY > AB
• C. XY = AB
• D. Can't be predicted

Answer 1

The correct option is A AB > XY

More is the difference in lattice energy (cost) and hydration energy (gain), more will be the solubility of a given compound.
For XY,
Hydration energy - Lattice energy
= 1000 kJ/mol - 400 kJ/mol
=600 kJ/mol
For AB,
Hydration energy - Lattice energy
= 2000 kJ/mol - 600 kJ/mol
= 1400 kJ/mol
So, the difference in lattice energy and hydration energy is more for AB as compared to XY. Hence, AB is more soluble in water.