Question

The alkali metal halide is soluble in water but $LiF$ is insoluble because
A. It’s atmospheric
B. $Li - F$ highly ionic
C. Its lattice energy is high
D. $L{i^ + }$is least hydrated

Answer 1

Hint: The third atom in the periodic table is $Li$, which has a small atomic radius. The chemicals' lattice enthalpies and radius how they affect the solubility of any compound.

Complete Step by Step Solution:
The difference in the characteristic is caused by the anion's nature and a few factors affecting solubility.

Let's look at the variables that influence a substance's solubility first.
- Lattice enthalpy of lattice energy and hydration enthalpy are the two basic concepts that pertain to solubility.
- A product's solubility is inversely proportional to lattice energy, but directly proportional to hydration energy, i.e., solubility hydration energy
- Solubility increases with increasing hydration energy and decreases with decreasing lattice energy.

Let's now quickly review the concepts of lattice energy and hydration energy.
- Lattice energy is therefore always defined as the amount of energy or enthalpy needed to break down a mole of a substance into its component ions.
- Or, if speaking of solids, the energy needed to dissolve the ionic bonds that make up the lattice. Lattice energy is primarily influenced by two variables: charge and size.
- The lattice energy increases when size reduces and charge rises, and vice versa. Hydration energy is the energy released when one mole of a material is hydrated.
- Li and F $LiF$ in have virtually identical atomic radii but are much smaller in size. Due to the ions' close proximity and very small size, there will be a greater amount of electrostatic attraction between them.
- Additionally, due to their high lattice enthalpy and low hydration energy in $LiF$, they are insoluble.
So, the alkali metal halide is soluble in water but $LiF$ is insoluble because of its high lattice energy i.e. option C is correct.

Note: The solubility of a substance is significantly influenced by the composition of the compounds. Ionic chemicals are more soluble than covalent compounds. Water dissolves polar molecules more readily in ionic compounds because they are polar, whereas covalent compounds are nonpolar by nature.